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International Journal of Heat and Mass Transfer
Journal Prestige (SJR): 1.498
Citation Impact (citeScore): 4
Number of Followers: 250  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0017-9310 - ISSN (Online) 0017-9310
Published by Elsevier Homepage  [3159 journals]
  • A study on the measurement and prediction of LED junction temperature
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Dongjun Lee, Hyunjin Choi, Sihun Jeong, Chang Hwan Jeon, Daehoon Lee, Jiseok Lim, Chan Byon, Jungwook ChoiAbstractIn this study, an innovative method for the measurement of the LED junction temperature is proposed. In the proposed technique, the temperature values at the LED chip surface, at the solder joint, and at a substrate point in the vicinity of the LED are measured, and the results are compared with the junction temperature measured by transient thermal measurements method. The aforementioned three temperature values are precisely measured via an IR thermometry and thin wire thermocouple. For the demonstration of the feasibility of the IR thermometry to the LED chip surface, the spectral distribution of the LED emission is analyzed using a spectroradiometer. The results show that there is negligible IR irradiation at the LED, suggesting no IR-induced interference is expected for the surface temperature estimation. In order to validate the experimentally obtained temperature distribution, an FEM-based numerical study is also performed. The experimental and numerical results are shown to agree well to each other within 15%. Based on the results, an empirical equations that correlate the junction temperature and the temperature at the solder joint, substrate, and surface of LED are developed. In addition, we show that analyzation of the structure function containing thermal resistance data of LED package obtained from the transient thermal measurement can yield a good interpretation in regard to the thermal resistance of the LED itself. The proposed methodology can act as a good guideline for the thermal management of the LED-related products.
       
  • Heat transfer analysis of nanofluid based microchannel heat sink
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Mohammad Zargartalebi, Jalel AzaiezAbstractHeat generation in miniature electronic devices is a limiting factor that often adversely affects device performance. One prominent remedy for this problem is to adopt nanofluid based microchannel heat sinks embedded with pin fins. The performance of these heat sinks depends on their geometry and coolant properties. Aside from these geometrical aspects, there is a dearth of studies on the effects of nanoparticle properties on heat transfer enhancement. In this study, the effects of nanoparticle properties on heat removal performance are modeled using a nanofluid two-component model. It is shown that the nanoparticle distribution plays important roles in heat transfer, and, unlike homogeneous nanofluid models, the flow patterns in the system follow the nanoparticle distribution. Moreover, it is found that the influence of nanoparticles on heat transfer depends both on the pin size and the flow regime. While there is a monotonic dependency between the nanoparticle effect and the pin size at small Reynolds numbers, this effect is non-monotonic at high Reynolds numbers. Nanofluid viscosity is also shown to have adverse effects on heat transfer improvement, and the effect is more detrimental as the inertial forces increase. The particle size and surface energy are also found to change the whole picture of heat removal process due to particle agglomeration and deposition. Therefore, based on the nanoparticle properties, a characteristic curve is introduced, using which, nanoparticles can safely improve heat transfer.
       
  • A fast and accurate temperature prediction method for microfluidic cooling
           with multiple distributed hotspots
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Yudan Pi, Jing Chen, Min Miao, Yufeng Jin, Wei WangAbstractAs the feature size decreases and integration degree increases, integrated circuits face a serious thermal challenge. Microfluidic cooling (i.e., forced convection of coolant inside micrometer-sized channels) has been regarded as a promising solution for the growing challenge of heat dissipation inside electronic devices. However, to the best of authors’ knowledge, the cooling performance of fluids inside microchannels is usually formulated under a uniform heat source, which is not the case in real applications where hotspots are distributed. The effect of the size of multiple distributed hotspots on microfluidic cooling has not previously been investigated. By implementing micro/nanofabrication technologies, hotspots with feature sizes of 50 µm, 100 µm, and 200 µm, were designed and fabricated on an 80-µm-thick Si substrate to mimic multiple distributed hotspots. Parallel microchannels, which were 60 µm deep, 50 µm wide, and 3440 µm long, were prepared for microfluidic cooling. In each single-hotspot heating experiment, a fitting parameter of the normalized heat transfer coefficient (h) was extracted from the power input and the local temperature excess based on the thermal spreading resistance model. The results indicated that h, i.e. the cooling performance on the hotspot, decreased with hotspot size. Therefore, in cases with varied hotspot sizes on a single chip, separate thermal analysis for each hotspot may be required to correctly predict microfluidic cooling performance. A simplified model based on the superposition principle was proposed to predict the temperature excess of multiple distributed hotspots with microfluidic cooling. The method was experimentally verified to attain a deviation less than 15%. Computation time was noticeably reduced from more than four hours (for a full-scale numerical simulation) to several minutes after implementing the simplified model.
       
  • A numerical analysis of the effect of heat recovery burners on the heat
           transfer and billet heating characteristics in a walking-beam type
           reheating furnace
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Alex M. García, Andrés A. AmellAbstractThe present study presents a numerical simulation of the effects of using self-recuperative burners on the performance of a walking-beam reheating furnace. The study was done using CFD (Computational Fluid Dynamics) simulations where a low computational cost method was implemented to simulate the billet heating as a steady state system. The preheating temperature of the air was defined as a function of the air mass flow and the flue gas temperature in each burner, using a UDF (User-Defined Function). The results of the billet heating profile were validated with experimental measurements in a furnace not utilizing heat recovery and showed good agreement with a maximum deviation of 54 K. Efficiency was found to increase from 32.7% to 48.5% with the use of self-recuperative burners. This result was reflected in a fuel consumption decrease of 31.3%, or an increase in furnace production of 51.3%. The heat transfer in the furnace and the billet heating characteristic were analyzed, which were observed to have changed with the different burners. This effect was lesser when the thermal input was decreased, and greater when the production was increased or when both remain constant. With and without heat recovery, radiation represents about 90% of the total heat flux on the billets. Due to the importance of radiation, solid and gas radiation were also analyzed. An improvement upon a methodology found in the literature was proposed. Using this new methodology it was found that, for the furnace evaluated, around 25% of the radiation absorbed by the billets comes from the flue gases. The effect of defined a constant billet emissivity on the results of the simulation was also discussed.
       
  • Analysis of modular composite heat pipes
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Keith Coulson, Sanjiv Sinha, Nenad MiljkovicThermal management requirements are becoming progressively more challenging as computing density increases due to the scaling down of electronic components. Improved thermal management schemes are necessary in power-dense systems to prevent thermal failure caused by excessive thermal cycling, optical misalignment, or exposure of instruments to environmental temperature extremes. To handle the extreme heat flux requirements of modern electronics (∼1 kW/cm2), two-phase heat transfer devices are used due to the high latent heat of phase change leading to well-managed temperature excursions during high heat dissipation events. To improve specific performance, manufacturing cost, and thermo-mechanical properties, we have developed a composite heat pipe model that utilizes differing materials for the adiabatic and evaporator/condenser sections. These composite heat pipes can be fabricated and installed for a fraction of the cost, while allowing for almost limitless customization, while maximizing specific heat transfer performance. We developed a comprehensive thermal-hydraulic model of the composite heat pipe performance that accounts for the pressure driven flow of the vaporized working fluid, the pressure drop over the length of the wick, and the thermal resistances governed by the wall, wick, liquid, and vapor. We used the model to show that the composite heat pipe has the potential for identical effective thermal conductivity when compared to its all metal counterpart, with drastic improvement (≈1000%) in specific performance. Furthermore, we use the model to perform sensitivity analysis and parametric multi-objective design optimization with respect to specific performance maximization and cost minimization. Our work not only presents a comprehensive model of composite heat pipe thermal-hydraulic performance, but offers a design platform for the development of next generation thermal dissipation devices that reduce cost and weight, and maximize manufacturability and implementation flexibility through modular design and integration schemes conducive to additive manufacturing techniques such as 3D printing.Graphical abstractGraphical abstract for this article
       
  • Element differential method for solving transient heat conduction problems
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Kai Yang, Geng-Hui Jiang, Hao-Yang Li, Zhi-bo Zhang, Xiao-Wei GaoAbstractIn this paper, a new numerical method, Element Differential Method (EDM), is developed for solving transient heat conduction problems with variable conductivity. The key point of this method is based on the direct differentiation of shape functions of isoparametric elements used to evaluate the geometry and physical variables. A new collocation method is proposed for establishing the system of equations, in which the governing differential equation is collocated at nodes inside elements, and the flux equilibrium equation is collocated at interface nodes between elements and outer surface nodes of the problem. Attributed to the use of the Lagrange elements that can guarantee the variation of physical variables consistent through all elemental nodes, EDM has higher stability than the traditional collocation method. The other main characteristics of EDM are that no variational principle or a control volume are required to set up the system of equations and no integrals are included to form the coefficients of the system. Based on the implicit backward differentiation scheme, an unconditionally stable and non-oscillatory time marching solution scheme is developed for solving the time-dependent system equations. Numerical examples are presented to demonstrate the accuracy and efficiency of the proposed method.
       
  • Thermal performance of a novel crushed-rock embankment structure for
           expressway in permafrost regions
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Minghao Liu, Wei Ma, Fujun Niu, Jing Luo, Guoan YinAbstractThe current crushed-rock interlayer structure, which was successfully adopted in construction of the Qinghai-Tibet Railway, cannot maintain the foundation stability of expressways in permafrost regions because of the strong heat absorption of the wide and dark-colored asphalt pavement surface. To satisfy the higher cooling requirement of expressways, a novel crushed-rock interlayer structure, which especially focuses on enhancing the cooling performance on the embankment core, is presented. A heat transfer model, which includes air convection in the crushed-rock interlayer and the heat conduction with a phase change in the soil layers, was developed to simulate the temperature evolution of a full-scale testing expressway embankment section built in Huashixia, the Qinghai-Tibet Plateau. The numerical results indicated that the new structure has a significant cooling performance and especially plays an effective role in lowering the permafrost temperature beneath the centerline of the expressway. Moreover, the new structure has the benefit of maintaining symmetry of the embankment temperature distribution. Therefore, it can be concluded that the new structure is an effective method to prevent permafrost degradation under expressways and can ensure the long-term thermal stability of embankments under the climate warming. The study provides reference and guidance for expressway design and construction in permafrost regions, such as the planned Qinghai-Tibet Expressway.
       
  • Evaporation of nanofluid sessile drops: Infrared and acoustic methods to
           track the dynamic deposition of copper oxide nanoparticles
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Ibrahim Zaaroura, Malika Toubal, Hilal Reda, Julien Carlier, Souad Harmand, Rabah Boukherroub, Aurélie Fasquelle, Bertrand NongaillardAbstractIn this work, we investigated the precipitation of 0.05%wt copper oxide nanoparticles in a sessile droplet during the evaporation process. We used two complementary methods to analyze the precipitation process of the nanoparticles at the solid/liquid interface: an optical one coupled to an infrared thermography method and an acoustic method. From the optical observation, using a Keyence microscope on the rear side of a transparent glass substrate coated with a silane layer, the precipitation process of the nanoparticles was successfully monitored by measuring the mean intensity density (ID‾) above the substrate by using ImageJ software. The acoustic method, based on a high frequency echography principle, allowed to monitor the deposition phenomenon of the particles above a non-transparent silicon substrate having similar silane coating as the glass substrate at room temperature. The time from which the nanoparticles begin to settle at the bottom of the substrate, obtained from the acoustic method, corroborated the one obtained from the optical one. Moreover, an estimate of the particles concentration throughout the process was deduced. The effect of substrate temperature and substrate wettability have also been studied experimentally and investigated using only the optical method and the infrared thermography one. An infrared camera from the top was employed to observe the temperature effect on the precipitation of the nanoparticles. Furthermore, when the substrate temperature exceeded 60 °C, co-existence of the thermal Marangoni flows was observed. It is expressed as a temperature gradient at the droplet liquid/air interfaces. The result showed the effect of these cells due to Marangoni effect on the nanoparticles’ stability.
       
  • Study on the migration of gas kicks in undulating sections of horizontal
           wells
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Yonghai Gao, Xiaohui Sun, Tianhua Zhao, Zhiyuan Wang, Xinxin Zhao, Baojiang SunAbstractUndulations are typically encountered in horizontal wells. Gas gathers at the top of undulating sections at low liquid velocity or well shut-in conditions. Thus, a gas slug is formed if gas kicks occur because of buoyancy, which makes well control more complex and difficult. In this paper, the storage and removal processes of the gas slug are simulated by experiments and the migration of the gas slug are analyzed. The results indicate that a minimum circulation velocity is required to remove the gas slug for a certain size and shape of undulating section of horizontal well. In addition, a migration model of gas kicks in undulating sections of horizontal wells is proposed based on the theoretical analysis. The model considers the effects of density difference, degree of curvature, surface tension, viscosity, and pipe diameter on gas slug removal rate and shows a good consistence with experimental results.
       
  • On the temperature equation in a phase change pseudopotential lattice
           Boltzmann model
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Qing Li, J.Y. Huang, Q.J. KangAbstractIn a recent paper by Gong et al. [19], the researchers claimed that in the previous models the derivation of the target temperature equation for liquid–vapor phase change is paradoxical because the equations of state for ideal gases and non-ideal gases are applied simultaneously, and therefore they proposed a modified pseudopotential lattice Boltzmann (LB) model for liquid–vapor phase change. In this technical note we clarify that the modified phase change pseudopotential LB model proposed by Gong et al. was based on a misunderstanding of the derivations in the previous studies as well as a mistake that they employed e=cvT, where e is the internal energy, to the derive the temperature equation for non-ideal gases.
       
  • A new method for prediction and analysis of heat and mass transfer in the
           counter-flow dew point evaporative cooler under diverse climatic,
           operating and geometric conditions
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Yangda Wan, Jie Lin, Kian Jon Chua, Chengqin RenAbstractDew point evaporative cooler, regarded as a zero polluting and energy efficient cooling device, has evolved to be a key technology in air-conditioning systems. The water evaporating process in the cooler is a key performing factor as it leads to the heat sink phenomenon. The cooling effectiveness is dictated by its heat and mass transfer coefficients. The conventional methods (mean temperature difference and integration methods) of obtaining these coefficients have limitations. In this work, a new method to determine these coefficients is proposed. Firstly, a NTU-Le-R model is installed to detect these coefficients. It is based on the outlet data of the dew point evaporative cooler. Next, a two-dimensional computational fluid dynamic model is developed to simulate the evaporative cooling process within the cooler and compute the outlet data for the NTU-Le-R model. Upon validation, results from the computational fluid dynamic model demonstrate close agreement to within ±6.0% with results acquired from experiments. Finally, the effects of the various conditions on the heat and mass transfer coefficients, including climatic, operating and geometric conditions, are judiciously investigated. The new proposed method has the capability to capture the essential boundary conditions to precisely obtain the transfer coefficients. In contrast to existing practices that combine the assumption of the Nusselt number under constant surface heat flux or temperature conditions with the Chilton-Colburn analogy. This new method simplifies computation while providing accurate data to realize optimum design of the dew point evaporative cooler.
       
  • Use of AHFM for simulating heat transfer to supercritical fluids:
           Application to carbon dioxide data
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): A. Pucciarelli, W. AmbrosiniAbstractThe present paper reports the results of analyses concerning heat transfer to supercritical pressure fluids, performed by adopting a k − ε turbulence model modified in association with the AHFM model, here used for calculating both buoyancy effects and the turbulent heat flux. The promising capabilities of this approach were already highlighted in past studies and the present paper represents a further step in this line of research.Experimental data concerning supercritical carbon dioxide flowing in tubes are here considered, with operating conditions involving both high and low mass flux values and spanning from relatively low inlet temperatures to values higher than the pseudocritical threshold. Some of the interesting features appearing in the experimental data are correctly reproduced by the model, which manages to predict reliable wall temperature trends, both qualitatively and quantitatively.The performed analyses, though reporting successes in a sufficiently wide range of operating conditions, suggest that some parameters of the proposed model should be varied in accordance with the boundary conditions, e.g. considering the mass flux, in order to improve predictions in the most challenging situations.
       
  • Effects of surface wettability on pool boiling of water using
           super-polished silicon surfaces
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Niloofar Mohammadi, Dani Fadda, Chang Kyoung Choi, Jungho Lee, S.M. YouAbstractPool boiling is an efficient cooling technique as a phase change heat transfer mode. Improvement of the boiling performance by postponing the surface dry-out point and increasing the critical heat flux is often necessary for assuring safe performance in many applications involving high heat fluxes. Recently, relevant surface modifications have become an attractive, yet practical approach for enhancing boiling performance. These modifications are implemented either by manipulating the surface wettability characteristics or imposing roughness onto the surface. In most cases, the mentioned modifications are dependent, where variation in one is accompanied by a change to the other. This study aims at the sole impact of surface wettability on the pool boiling performance with super-polished silicon surfaces with different wettability characteristics prepared by chemical vapor deposition and sputtering. Pool boiling experiments are conducted using these surfaces where the heat supply and temperature measurement were performed via an integrated state-of-the-art resistance-temperature detector and heater. The experimental results show a trend in increasing the critical heat flux value of the pool boiling for more wettable surfaces and quantitatively define a low limit for the critical heat flux. Moreover, nucleation and bubble behavior are also studied at incipience.
       
  • Effect of thermal anisotropy on binary alloy dendrite growth
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Amman Jakhar, Anirban Bhattacharya, Prasenjit Rath, Swarup Kumar MahapatraAbstractA numerical model to study the effect of thermal anisotropy on binary alloy dendrite growth is presented. The model is based on the volume averaged enthalpy method with explicit surface tension anisotropy for crystal orientation. Thermal anisotropy is incorporated using anisotropic thermal conductivity in the energy equation. This is done by splitting the anisotropic conductivity into two parts, equivalent isotropic conductivity and anisotropic departure source term, enabling the use of a conventional isotropic solver to model anisotropic heat transfer. The proposed model is applied to study the effect of thermal anisotropy ratio on tip velocity, aspect ratio and equivalent radius of an equiaxed grain growing in an undercooled binary alloy melt. It is found that the thermal energy stored in the grain during solidification plays an important role in interface evolution, and thus anisotropic conductivity in the solid affects the grain morphology. There is a consistent increase in the aspect ratio of grains with increase in thermal anisotropy ratio, although the grain volume remains almost invariant. Due to unequal growth rates of the perpendicular arms, severe distortion of the solid crystal is seen at higher thermal anisotropy ratios. The model is further extended to study the growth of multiple dendrites in order to simulate microstructure evolution with thermal anisotropy. It is observed that thermal anisotropy significantly affects the grain morphology at low grain density but has a smaller influence at high grain density as compared to other governing factors such as solute transport.
       
  • Effect of thermal activity on critical heat flux enhancement in
           downward-hemispherical surface using graphene oxide coating
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Min Ho Lee, Hyo Heo, In Cheol BangAbstractCritical heat flux (CHF) enhancement is needed to ensure a proper safety margin for the in-vessel retention through external reactor vessel cooling (IVR-ERVC), which is a decay heat removal strategy in the nuclear power plants. To enhance the cooling capability of IVR-ERVC, graphene oxide (GO) was coated on a boiling surface, with a reduced geometry to that of the reactor pressure vessel (RPV). This study experimentally investigated the effect of the GO coating on the CHF. A R-123 refrigerant was used as a working fluid to mitigate the wetting effect. Various concentrations of nanofluids were used in the experiments (0.01, 0.03, and 0.05 vol%) to examine the effect of thermal activity on the CHF. Because the thermal effusivity of the GO coating layer was higher than that of the copper heater, the thermal activity of the surface increased with thicker GO coating layers. The CHF limit of the GO-coated surface was enhanced by 38% compared to that of the bare surface due to increased thermal activity. Periodic bubble behavior was also observed near the CHF and visual criterion for CHF observation is detailed herein.
       
  • Towards understanding the effects of irradiation on quenching heat
           transfer
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Arunkumar Seshadri, Bren Phillips, Koroush ShirvanAbstractQuench and rewet characteristics at low pressure depends on the heated sample surface characteristics. The rate of decrease in the maximum temperature during the quench of heated specimen depends on its surface, material, and the quenching environment. The effect of irradiation on the quench heat transfer, particularly gamma irradiation has been investigated previously for metallic rodlet specimens. Some of the previous studies demonstrated an improvement in wettability and Leidenfrost temperature in oxide surfaces as a result of exposure to gamma irradiation. However, the mechanism behind such improvements has not been studied in detail. The present work reports the experiments carried out to understand the wettability and quench performance of Zircaloy-4, the nominal fuel cladding material for nuclear energy, and chrome-coated Zircaloy rodlets, proposed coating material to increase Zircaloy’s accident tolerance in response to Fukushima disaster, under gamma irradiation. The goals of the experiments were to delineate the effect of radiation on the transient pool boiling behavior during the quenching of the surfaces and assist the development of a mechanistic model. The results of water quenching and contact angle studies showed a higher Leidenfrost temperature and wettability in both samples exposed to gamma irradiation. Further, to understand the effects of gamma irradiation, independent studies with ultraviolet ozone treatment were performed and microscopic images of the gamma irradiated samples were analyzed. It was found that formation of oxide micropores in the samples exposed to gamma irradiation was the primary mechanism for enhanced wettability as well as higher Leidenfrost temperature.
       
  • Elucidation of keyhole induced bubble formation mechanism in fiber laser
           welding of low carbon steel
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Dongsheng Wu, Xueming Hua, Lijin Huang, Fang Li, Yan CaiAbstractLaser welding experiment with the aid of glass, and numerical simulation are carried out to study the keyhole behavior and keyhole-induced bubble formation. Two mechanisms are responsible for keyhole-induced bubble formation. The first mechanism is the strong fluid flow inside the weld pool, and the capillary instability of the whole keyhole, causing the collapse between rear keyhole wall and front keyhole wall. This mechanism contributes to most of keyhole-induced bubble formation. The second mechanism is the instability of the rear keyhole wall caused by the increase absorption of laser energy reflected by the bulge at front keyhole wall. The breaking of molten bridge is analyzed based on static pressure balance. The molten bridge with large curvature and low temperature is difficult to be broken. Bubble coalescence can be clearly observed at the bottom of the weld pool. Large bubble and small bubble have high coalescence efficiency. The bubbles at keyhole bottom have more time to escape without broken by laser beam, and the bottom part of rear keyhole wall is more easily depressed, so bubbles are easily formed at the keyhole bottom.
       
  • Heat transfer enhancement for laminar flow in a tube using bidirectional
           conical strip inserts
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Peng Liu, Nianben Zheng, Feng Shan, Zhichun Liu, Wei LiuAbstractIn the present work, a novel tube insert (bidirectional conical strip inserts) is proposed, and the heat transfer performance and flow characteristics of this insert are studied numerically. Effects of three geometric parameters (numbers of bidirectional conical strip (n), central angle (α) and pitch ratio (P∗ = p/D)) are also investigated. The results indicate that cold fluid in the core region and the hot fluid near the tube wall are rapidly exchanged as the fluid flows through the bidirectional conical strip, and multiple longitudinal swirling flows are formed downstream of the bidirectional conical strip. Therefore, the heat transfer (the Nusselt number) is significantly enhanced by 2.35–9.85 times compared to the smooth tube. Moreover, because of the cooperation between the forward and the reverse conical strips, the formation of the dead zone and eddy on the back of the conical strips is inhibited. Thus, the increase in flow resistance is smaller than many other published works, as the friction factor is enhanced to 2.37–21.18 times of the smooth tube. The overall heat transfer performance (PEC value) is located in range of 1.75–3.93. Both the Nusselt number and friction factor increase with the increasing numbers of bidirectional conical strip, central angle and the decreasing pitch ratio. However, the friction factor is more sensitive to geometric parameters, so the maximum overall heat transfer performance (PEC value) is obtained at moderate geometric parameters (n = 3, α = 40° and P* = 3). In addition, Correlation formulas for Nusselt number and friction factor are derived.
       
  • Analysis on heat transfer and pressure drop of fin-and-oval-tube heat
           exchangers with tear-drop delta vortex generators
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Gaofeng Lu, Xiaoqiang ZhaiAbstractNumerical simulations are performed to examine the thermal and flow characteristics of tear-drop delta vortex generators (VGs) on the fin surfaces of fin-and-oval-tube heat exchangers. The VGs deployed in a “common flow up” configuration behind tubes can induce longitudinal vortices and reduce the area of wake region, which results in significant heat transfer enhancement and negligible augmentation of pressure drop compared with plain fins without VGs. The heat transfer performance and pressure loss are analyzed using the dimensionless parameters j/j0, f/f0, and R = (j/j0)/(f/f0)1/3 with ReDc ranging from 255 to 1533. The results indicate that the tear-drop delta VGs have a better thermal-hydraulic performance than plane delta VGs and the value of R reaches as high as 1.06–1.23 at the ratio of division for chord length (l1/l2) being 2/3. Further parameters study reveals that when the height of VGs is 0.6 times of fin pitch, the lateral length is 0.3 times of fin pitch, and the chord length is 1.2–1.4 times of fin pitch, the optimal overall performance can be obtained. The mechanism of heat transfer enhancement is investigated by intensity of secondary flow and field synergy principle. It suggests that for the case with higher Nusselt number, the corresponding secondary flow intensity is higher and the synergy angle is smaller. In addition, for each case, where the Nusselt number is higher, the secondary flow intensity is higher and the synergy angle is smaller.
       
  • Internal mass and heat transfer between a single deformable droplet and
           simple extensional creeping flow
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Anjun Liu, Jie Chen, Zhenzhen Wang, Zai-Sha Mao, Chao YangAbstractThis work studied numerically the internal mass/heat transfer of a deformable droplet immersed in a simple extensional flow. The droplet would deform gradually from prolate spheroid to ‘peanut’ in uniaxial extensional flow, or from oblate spheriod to ‘red-blood-cell’ in biaxial extensional flow. Based on the analytical solution of Stokes flow over a deformable droplet, the convection-diffusion transport equation was numerically solved by the finite difference method. The results show that the heat/mass transfer behaviors of a deformable droplet were different when compared with that of a spherical one. The effects of Pe (1  ≤  Pe  ≤  10000), capillary number Ca (0  ≤  Ca  ≤ 0.5), viscosity ratio λ (0.01 ≤ λ ≤ 100) and the extensional flow direction on the Sh and mean concentration were numerically investigated. It shows that the internal mass/heat transfer rate was always enhanced with the increased degree of drop deformation in the diffusion-dominated case in both uniaxial/biaxial extensional flows. However, in the convection-dominated case, the flow direction has opposite influence on transport rates of mass/heat transfer with different deformation rates. The stabilized mass transfer rate decreased for droplets with different deformation in the order: 'red-blood-cell' shaped droplet, oblate droplet, prolate droplet and 'peanut' shaped droplet. At last, we proposed the empirical correlations to predict the internal mass/heat transfer rate of a deformable droplet (by adding the parameter Ca to represent the deformation of a droplet) in simple extensional flow.
       
  • An entransy based method for thermal analysis and management of high heat
           density data centers
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Hao Tian, Hang Liang, Zhen Li
       
  • Simulations of saturated boiling heat transfer on bio-inspired two-phase
           heat sinks by a phase-change lattice Boltzmann method
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Xiaojing Ma, Ping Cheng, Xiaojun QuanAbstractPool boiling heat transfer from four types of micro-pillar heat sinks with different wettability patterns is simulated numerically with the latest version of liquid-vapor phase-change lattice Boltzmann model. Effects of pillar geometry and wettability on bubble dynamics are investigated. It is found that bubbles will nucleate either on the hydrophobic pillar top or on the hydrophilic cavity bottom between micro-pillars, depending on wettability and local wall temperature. Among the four types of micro-pillar heat sinks with hybrid wettability patterns, it is found that the bio-inspired heat sink (with hydrophobic pillar tops and hydrophilic base) has the best boiling heat transfer performance with the following desirable features: (i) unique characteristics of orderly separation of vapor and liquid paths at low superheats, (ii) hydrophobic surface characteristics where residual bubbles on hydrophobic pillar tops provide faster bubble departure frequency, (iii) triple phase lines are pinned at corners of micro-pillar, restricting expansion of bubbles into film boiling at high superheats. Simulated results show that geometry of micro-pillars and wettability patterns greatly influence transition boiling regime including the maximum heat flux (CHF) and the Leidenfrost temperature, resulting in pool boiling curves with widely different shapes.
       
  • Heat transfer and pressure drop characteristics of ammonia during flow
           boiling inside a horizontal small diameter tube
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Yuping Gao, Shuangquan Shao, Binfei Zhan, Yiyu Chen, Changqing TianAbstractIn this article, a series of experiments was conducted to investigate the flow boiling heat transfer and pressure drop characteristics of ammonia in a 4 mm horizontal plain tube. The experiments were performed for heat fluxes at 9 and 21 kW m−2 K−1, mass flux from 50 to 100 kg m−2 s−1, and saturation temperature from −15.8 to 5 °C. The experimental results show that with the increase of heat flux, the heat transfer coefficient increases. Meanwhile, it also increases with a rise in mass flux in the low vapor quality region, whereas reversed situation can take place in the high vapor quality region when the saturation temperature is decreased. The saturation temperature has little effect on the heat transfer coefficient in the low vapor quality region, however at higher mass fluxes, the heat transfer coefficient can decrease with decreasing saturation temperature in the high vapor quality region. The comparisons of the experimental data with existing correlations for flow boiling heat transfer coefficient show that Gungor and Winterton correlation can give good agreement with mean absolute deviation of 19.6% even though it is developed for turbulent flow. The adiabatic two-phase frictional pressure gradient increases with the increase of vapor quality and mass flux, while decreases with the increase of saturation temperature. The comparisons with existing correlations for two-phase frictional pressure gradient indicate that Müller-Steinhagen and Heck correlation can predict the experimental data well with mean absolute deviation of 16.1% and 93.4% of the data is within the ±30% error band.
       
  • Experimental study of human thermal plumes in a small space via
           large-scale TR PIV system
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Jiayu Li, Junjie Liu, Jingjing Pei, Krishna Mohanarangam, William YangAbstractIn small occupied spaces such as vehicle cabins, in-depth information about human thermal plumes can be important for designing ventilation systems, especially in the case of displacement ventilation. In this study, large-scale time-resolved particle image velocimetry measurements were performed to reveal airflow characteristics of thermal plumes inside a small space with high temporal and spatial resolutions. The measured time-averaged velocity showed that the development of thermal plumes was limited by the small space, with maximum vertical velocity of 0.184 m/s above the head. The standard deviation of velocity and the turbulence intensity (TI) indicated high fluctuation characteristics, with TI of approximately 0.4 in the mainstream area. With these time-resolved data, the integral, Taylor and Kolmogorov scales were calculated, which provided recommended grid sizes and time steps for different numerical simulations. For investigation of instantaneous characteristics and vortex structures, three vortex identification parameters were compared. The vorticity index identified bulky attached and detached vortexes around the head; the Q-criterion revealed that the mainstream area was controlled mainly by deformation structures; and the λci criterion, which was the most effective means of identification, avoided the influences of deformation structures and focused only on the rotation structures with directions of rotation. Furthermore, multi-scaled characteristics of thermal plumes were revealed by proper orthogonal decomposition, and the period of ascending plumes was estimated as 5 s.
       
  • Characteristics and correlation of nozzle internal flow and jet breakup
           under flash boiling conditions
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Shangze Yang, Xuesong Li, David L.S. Hung, Min XuAbstractFlash boiling sprays utilize superheated fluid to enhance spray breakup via eruption of flash boiling bubbles near the nozzle exit. Extensive efforts have been made to interpret the underlying complex phase change physics associated with flash boiling sprays. However, the dynamic interaction between the gas phase and liquid phase of the flash boiling sprays has not been adequately investigated yet. This work adopts a two-dimensional optical transparent nozzle to study in-nozzle multiphase flow characteristics as well as spray characteristics outside of the nozzle. Both high-speed and low-speed measurements were carried out using optical diagnostic methods, and flash boiling sprays at different superheat levels were studied. With the experiments, the correlation between the internal flow and spray liquid jet breakup is established and the impact of the gas-liquid correlation on the properties of flash boiling sprays is presented. Furthermore, dynamic interaction between the gas phase and liquid phase in the nozzle and out of the nozzle is analyzed with a center of mass scheme. It is found that the dynamic features of the flash boiling sprays are closely connected with the dynamics of the in-nozzle flow. Such observation suggests that modifying flash boiling bubble characteristics can potentially be utilized to actively control flash boiling sprays for improved spray performance.
       
  • Study on identification method of heat transfer deterioration of
           supercritical fluids in vertically heated tubes
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Qian Zhang, Huixiong Li, Xianliang Lei, Jun Zhang, Xiangfei KongAbstractPrediction of the heat transfer of supercritical fluids (SCFs), especially for heat transfer deterioration (HTD), is highly significant to the design and safe operation of supercritical boilers and advanced nuclear systems. To achieve higher predictive accuracy, heat transfer datasets of SCFs are usually classified as HTD cases and non-HTD cases using certain HTD identification methods, and prediction models, including empirical correlations and criteria of HTD occurrence, have been separately developed for HTD cases and non-HTD cases. Therefore, the rationality of HTD identification methods are crucial to the data classification and further development of high-precision prediction models but is seldom discussed in research. This paper first summarizes the existing identification methods of HTD to SCFs, and respective heat transfer datasets of supercritical water (SCW) and CO2 (SCCO2) are compiled. Based on these datasets, the accuracy of existing methods in identifying HTD cases and non-HTD cases is evaluated. The results show that, the most common identification method (Nu/Nudb 
       
  • Experimental study on the interfacial wave and local heat transfer
           
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Xiao Zong, Ji-ping Liu, Jun-jie YanAbstractAn experimental study on the interfacial wave and local heat transfer coefficient of stable steam jet condensation in a rectangular mix chamber was carried out. In experiments, the interfacial wave amplitude was obtained and analyzed, and an empirical correlation predicting the dimensionless wave amplitude was established. To evaluate the local average heat transfer coefficient, a thermal equilibrium model was developed, and the local average heat transfer characteristics were obtained and discussed. The results indicate that the interfacial wave amplitude increases with water mass flux and the axial dimensionless position, decreases with the steam mass flux, and changes little with inlet water temperature. The local average heat transfer coefficients are within the range of 0.98–6.24 MW/m2 °C, and they increase with the interfacial wave amplitude. The interfacial fluctuation could promote the steam jet condensation and corresponding heat transfer coefficients.
       
  • Comparative evaluations of thermofluidic characteristics of sandwich
           panels with X-lattice and Pyramidal-lattice cores
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Xin Jin, Beibei Shen, Hongbin Yan, Bengt Sunden, Gongnan XieAbstractThis study compares the thermo-fluidic characteristics of sandwich panels with the X-lattice and the Pyramidal lattice at a given porosity and surface area density. The numerical model is validated against available experimental data at first. At a given Reynolds number in the range of 3100–5700, numerical results reveal that the X-lattice sandwich panel provides a 47–60% higher average overall Nusselt number. The special topology of the X-lattice induces counter-rotating spiral primary flow and more complex secondary flows, including one which becomes a longitudinal vortex later. The flow in the Pyramidal lattice sandwich panel is composed of a parallel primary flow and a counter-rotating vortex pair entrenched in the zone behind ligaments of the Pyramidal lattice. Compared with the Pyramidal lattice sandwich panel, endwall heat transfer of the X-lattice sandwich panel is enhanced by 75–97% and the ligaments surface heat transfer is enhanced by 85–97% at a given Reynolds number. It is also found that the friction factor of the X-lattice sandwich panel is about 2 times higher for the spiral primary flow and more complex secondary flows induced by the staggered ligaments. Finally, at a given pumping power, the cooling performance of the X-lattice is much better, too. Taking the identical fabrication method and cost into account, apparently the X-lattice is superior in engineering applications.
       
  • Heat and mass transfer characteristics of steam in a horizontal wellbore
           with multi-point injection technique considering wellbore stock liquid
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Shijun Huang, Meng Cao, Yun Xia, Xiao Chen, Menglu YangAbstractIn this paper, a novel model is proposed to study the variable mass flow process in a long horizontal well and to predict the distribution of thermophysical properties along the horizontal wellbore.First, a physical simulation device is designed to carry out a steam-injection experiment. Second, considering both the uneven distribution of steam and the effect of wellbore stock liquid, a steam-absorption model and a pressure drop model are proposed to predict the distribution of steam and pressure along the horizontal wellbore. Third, the effects of different parameters on steam distribution are analyzed in detail. The results indicate that: (1) an uneven employment phenomenon exists along the wellbore; (2) the pressure distribution along the wellbore is higher when wellbore stock liquid is taken into consideration; (3) the length of the unemployed section along the wellbore increases with an increase in the wellbore stock liquid viscosity; (4) the length of the unemployed section along the wellbore decreases with an increase in the steam injection rate; and (5) the reasonable wellbore length can prevent an unemployed section along the wellbore.This paper presents a basic reference for engineering for parameter optimization as well as for the prediction of steam distribution along the horizontal wellbore.
       
  • Electro- and thermophysical properties of water-based nanofluids
           containing copper ferrite nanoparticles coated with silica: Experimental
           data, modeling through enhanced ANN and curve fitting
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Abdullah A.A.A. Alrashed, Arash Karimipour, Seyed Amin Bagherzadeh, Mohammad Reza Safaei, Masoud AfrandA new homogeneous nanofluid of copper ferrite nanoparticles coated by silica dispersed in distilled water as the base fluid is prepared in a way to avoid settling and agglomeration. The values of dynamic viscosity and electrical conductivity at various temperatures and nanoparticles concentrations are experimentally measured. In addition, two empirical correlations are provided for them by the curve fitting approach. Moreover, the sensitivity analysis beside an enhanced artificial neural network is presented to accomplish the obtained results. The margin of deviations and experimental results versus those of correlations, imply the suitable accuracy of the proposed correlation. It is shown that more temperature corresponds to less dynamic viscosity; it also mildly increases the electrical conductivity. However, the effect of nanoparticle concentrations is more significant.Graphical abstractXRD pattern for dry CuFe2O4/SiO2 nanoparticles.Graphical abstract for this article
       
  • New adiabatic and condensation two-phase flow pattern maps of R14 in a
           horizontal tube
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Qinglu Song, Gaofei Chen, Zhiqiang Yang, Haocheng Wang, Maoqiong GongAbstractHeat transfer and pressure drop for two-phase flow are closely related to corresponding flow patterns. In this work, an experimental investigation on adiabatic and condensation two-phase flow patterns and their transitions of tetrafluoromethane (R14) in a horizontal tube with inner diameter of 4 mm was conducted. Experiments were implemented at mass fluxes from 200 to 650 kg/(m2 s), saturation pressures from 1 to 3 MPa and heat fluxes from 8.2 to 28.2 kW/m2. The observed adiabatic flow patterns were compared with six well-known flow pattern maps, none of them can predict all the transition lines accurately. Therefore, a new dimensionless number S1, which takes account of inertia force, gravity force, shear force and surface tension force, was proposed to develop the new adiabatic flow pattern transition criteria. Eight groups of data were compared with the new adiabatic flow pattern map, most of the flow pattern data can be accurately predicted. What’s more, in order to explain the effect of heat flux on condensation flow pattern transitions, another new dimensionless number S2 was proposed by combining the dimensionless number S1 and boiling number together. Finally, a condensation flow pattern map was proposed based on the dimensionless number S2.
       
  • Experimental study on thermal performance of a pulsating heat pipe with
           surfactant aqueous solution
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Meibo Xing, Ruixiang Wang, Rongji XuAbstractIn this work, the thermal performance of pulsating heat pipe (PHP) using surfactant aqueous solution as working fluid was experimentally investigated. The cetyl trimethyl ammonium bromide (CTAB) was applied for preparation of surfactant solution in the concentration range of 0.025–0.25 wt%. It is found that the adding of CTAB can significantly reduce the surface tension and improve the wettability, thus enhance heat transfer between the tube wall and working fluid due to the increase in the liquid film area. The thermal performance of CTAB solution PHP depends greatly on the input power, filling ratio and surfactant concentration. Experimental results indicate that the heat transfer enhancement of PHP with CTAB solution is apparent at higher input power when the concentration is very high. Comparing to the water PHP, the thermal resistance of 0.25 wt% CTAB solution is decreased by 48.5% at the input power of 100 W when filling ratio is kept as 50%.
       
  • Numerical investigation of oxygen thermochemical nonequilibrium on
           high-enthalpy double-cone flows
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Jiaao Hao, Chih-Yung WenAbstractHypersonic thermochemical nonequilibrium flows over a double-cone configuration are numerically investigated. Simulations with oxygen as the test gas are performed using different coupling models of vibrational excitation and dissociation, including a conventional two-temperature model as the baseline and an improved model established on elementary kinetics and validated against existing shock tube experimental data. For the condition with the highest total enthalpy, the improved model predicts a larger separation region and greater peak heat flux with relative differences of 20.3% and 29.2%, respectively, compared with the baseline two-temperature model. The differences are attributed to inaccurate modeling of the vibration–dissociation coupling effects by the conventional two-temperature model, which overestimates the post-shock degree of dissociation and underestimates the post-shock temperature. The size of the separation bubble is therefore altered due to the change in its density. These findings may help to explain the large discrepancies found between numerical results and experimental data for high-enthalpy double-cone flows in hypersonic studies.
       
  • Optimization transpiration cooling of nose cone with non-uniform
           permeability
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Nan Wu, Jianhua Wang, Fei He, Liang Chen, Bangcheng AiAbstractWith the development of active thermal protection techniques (TPTs), optimization transpiration cooling (OTC) design, to enhance the cooling effect in stagnation regions and decrease coolant load, has become a critical issue in the research and development of hypersonic vehicles. One of the possible OTC approaches is using a non-uniform porous material to vary the coolant allocation within pores. This paper presents an experimental and numerical investigation on the transpiration cooling performances of two wedge shaped nose cones. One is for OTC, made of a special porous matrix with non-uniform permeability to ensure the largest porosity near the stagnation point, and the other is for traditional transpiration cooling (TTC), consisting of a general uniform porous matrix. Surface temperature and cooling effectiveness of the two nose cones are investigated in the experiments. The data show that in comparison with TTC, OTC can effectively enhance the cooling effectiveness in stagnation regions through a locally high permeability, and improve the uniformity of the temperature distribution within the entire nose cone. To exhibit the coolant flow characteristics within the pores, two-dimensional numerical simulations are carried out by commercial software FLUENT, and the numerical method is validated by the experimental data. The numerical results indicate that OTC with non-uniform permeability can provide an optimized coolant allocation and decrease the driving force required by the coolant transport to the stagnation region.
       
  • Effects of geometric structures on flow uniformity and pressure drop in
           dividing manifold systems with parallel pipe arrays
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Wanqing Zhang, Angui Li, Ran Gao, Cheng LiAbstractDividing manifold systems have been extensively used in the areas of energy transfer and conservation. The design of uniform flow distribution is a critical issue for the enhancement of performance of the manifold system. In this study, the effects of the inlet Reynolds number and structural parameters (area ratio (AR), pipe pitch (Δl), height of convex head (hhead) and number of outlets (n)) on flow uniformity and pressure drop in the DMS–PPA have been numerically investigated and validated with experiment data. The non-uniform distribution in the manifold system has been quantified using the dimensionless parameter βi (flow ratio) and Φ (non-uniformity coefficient). The results indicate that the flow rate increases along the longitudinal direction of the manifold and becomes close to the average value in the 2nd and 3rd outlets. It is found that the Ф slightly drops with the Re rising, while the ΔPj would dramatically increase owing to the increasing inlet flow rates. The AR has the greatest influence on flow uniformity, and lower AR corresponds to a more uniform distribution. The corresponding Φ values increases from 0.00351 to 0.3885 when AR varies from 0.2844 to 4. Under the same inlet flow rate, the increase of n will lead to obvious flow non-uniformity. The superiority of flow performance in the DMS–PPA can be ascribed to the anti-parallel flow direction, and the ‘plenum chamber-like’ structure of the manifold. The optimsed geometric structures with 1 
       
  • Experimental investigations of the effects of the injection angle and
           blowing ratio on the leading-edge film cooling of a rotating twisted
           turbine blade
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Hai-wang Li, Feng Han, Zhi-yu Zhou, Yi-wen Ma, Zhi TaoAbstractExperimental investigations were performed to study the effects of the injection angle of cylindrical holes and the blowing ratio on the leading-edge-region film cooling of a twisted turbine blade under rotating conditions. The experiments were carried out at a test facility with a 1-stage turbine using the thermochromic liquid crystal (TLC) technique. All experiments were performed at a rotating speed of 574 rpm with an average blowing ratio ranging from 0.5 to 2.0. The Reynolds number was fixed at 6.3378 × 104 based on the mainstream velocity of the turbine outlet and the rotor blade chord length. CO2 was used as the coolant to achieve a coolant-to-mainstream density ratio of 1.56. The film-hole injection angles tested were 30°, 45° and 60°. The results show that both the injection angle and the blowing ratio have significant impacts on film cooling effectiveness. For α = 30° and α = 45°, the radial average film cooling effectiveness increases as the blowing ratio increases in all regions. For α = 60°, this effectiveness first increases and then decreases as the blowing ratio increases, with the case of M = 1.5 yielding the best average cooling performance. At each blowing ratio, the α = 30° case always yields the highest streamwise average film cooling effectiveness in the region of −4.3 
       
  • Theoretical study on the heat transfer characteristics of a plain fin in
           the finned-tube evaporator assisted by solar energy
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Guodong Qiu, Jian Sun, Yuanyang Ma, Jiagang Qu, Weihua CaiAbstractFinned-tube evaporators have been widely used in air source heat pumps. Coating a solar selective absorbing coating on the fin surface is proved an effective approach to improve the heat transfer effects of finned-tube evaporators using solar energy. However, currently, most attentions were paid to the performance improvement of heat pump systems assisted by solar energy, scarce of attentions were paid to the heat transfer characteristics of this kind of fin under solar radiation. Therefore, the heat transfer characteristics of this kind of fin under solar radiation were studied using the heat transfer theory. Based on the heat transfer models, the theoretical solution of temperature field was deduced, and its accuracy was validated by numerical simulation. The effects of various factors on the heat transfer characteristics of a plain fin were theoretically analyzed. The results showed that the solar radiation would lessen the convective heat transfer capacity and fin efficiency, and even make part of solar energy to release into the environment. The maximum loss of solar energy accounts for about 12.7% of the total solar energy, and twice the fin height only generates 60% increase of the total heat transfer capacity. In the condition of larger fin height and solar radiation, the smaller convective heat transfer coefficient will produce more total heat transfer capacity. This study is helpful to analyze this kind of heat transfer problem and guide the optimization design of finned-tube evaporators assisted by solar energy.
       
  • Film cooling characteristics on the leading edge of a rotating turbine
           blade with various mainstream Reynolds numbers and coolant densities
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Hai-wang Li, Feng Han, Hai-chao Wang, Zhi-yu Zhou, Zhi TaoAbstractThis paper reports on an experimental investigation of the influences of mainstream Reynolds number and coolant density on film cooling characteristics on the leading edge of a twisted turbine blade under rotational conditions. The experiments were carried out at a test facility with a 1-stage turbine using the thermochromic liquid crystal (TLC) technique. The mainstream Reynolds number varied from 4.4201 × 104 to 7.1797 × 104. All tests were carried out at three rotational speeds of 400 r/min, 500 r/min and 650 r/min to fix the rotation number at 0.0018. The coolant-to-mainstream density ratios were fixed at 1.04 and 1.56 with N2 and CO2 as coolants, respectively. The blowing ratio effect was also considered. The results showed that under the same blowing ratio, the averaged film cooling effectiveness on the measurement area increased with increasing mainstream Reynolds number for both coolant gases. Under the same Reynolds number, the span-wise averaged film cooling effectiveness increased as the blowing ratio increased for both coolant gases. Under the same Reynolds number and blowing ratio, higher-density coolant jets (CO2) provided higher averaged film cooling effectiveness than lower-density coolant jets (N2) on the measurement area. Overall, mainstream Reynolds number, blowing ratio and coolant density played significant roles in the film cooling characteristics of the leading edge under rotational conditions.
       
  • Solution of an inverse transient heat conduction problem in a part of a
           complex domain
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Piotr Duda, Mariusz KoniecznyAbstractThe purpose of this work is to formulate two simple methods which can be used to solve nonlinear inverse heat conduction problems in a part of a complex-shaped component in the on-line mode. The proposed methods can be useful if temperature measurements are carried out only in a selected part of an outsize element or if the whole element cannot be analysed due to the inverse heat conduction problem being ill-conditioned. It is assumed that the conductive heat transfer occurs through the surfaces separating the domain from the rest of the component. It is shown that the simplifying assumption of thermal insulation on these surfaces, which is often presented in literature, can cause significant errors. Compared to works published previously, if two additional unknown boundary conditions are introduced on the separating surfaces, the inverse problem conditioning deteriorates substantially. Despite this, stable solutions are achieved for “noisy measured data”.The presented methods can be used to optimize the power unit start-up and shutdown operation. They may also enable a reduction in the heat loss arising during the process and extend the power unit life. The methods presented herein can be applied in monitoring systems working both in conventional and nuclear power plants.
       
  • Local convective condensation heat transfer in horizontal double-layer
           three-dimensional dimple-grooved tubes
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Jingxiang Chen, Wei LiAbstractAn experimental study on local condensation heat transfer characteristics in two three-dimensional double-layer dimple-grooved tubes (2EHT tubes) and a smooth tube is performed using refrigerant of R410A. The smooth tube has an outer diameter of 12.7 mm and inner diameter of 11.07 mm. The 2EHT tubes have a nominal outer diameter of 12.7 mm and wall thickness of 0.8 mm. The enhanced surface areas of two 2EHT tubes are 1.02 and 1.03 times of the smooth tube, respectively. The present experiments are conducted to measure the local wall temperature when the mass flux ranges from 65 kg/(m2·s) to 210 kg/(m2·s), heat flux ranges from 10 kW/m2 to 35 kW/m2 and vapor quality ranges from 0.9 to 0.1. The saturation temperature is maintained at 40 °C. 248 experimental HTC data points are obtained and compared with six correlations. The results show that the measured local HTCs increase with increasing mass fluxes and decrease with increasing heat fluxes, and that the present correlations have a good predictability with smooth tube but cannot predict the HTC of 2EHT tubes. The proposed condensation correlation for 2EHT tubes is validated, and it predicts all experimental points within an error band of ±30%, and 94.25% of all test points within an error band of ±20%.
       
  • Flow condensation pressure oscillations at different orientations
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Lucas E. O'Neill, Issam Mudawar, Mohammad M. Hasan, Henry K. Nahra, R. Balasubramaniam, Jeffery R. MackeyAbstractInvestigation of two-phase flow dynamic behavior and instabilities has traditionally centered on phenomena present in boiling flows due to the safety critical nature of boiling in a variety of cooling applications. Analysis of pressure signals in condensing systems reveal the presence of relevant oscillatory phenomena during flow condensation as well, which may impact performance in applications concerned with precise system control. Towards this end, the present study presents results for oscillatory behavior observed in pressure measurements during flow condensation of FC-72 in a smooth circular tube in vertical upflow, vertical downflow, and horizontal flow orientations. Dynamic behavior observed within the test section is determined to be independent of other components within the flow loop, allowing it to be isolated and interpreted as resulting from physical aspects of two-phase flow with condensation. The presence of a peak oscillatory mode (one of significantly larger amplitude than any others present) is seen for 72% of vertical upflow test cases, 61% of vertical downflow, and 54% of horizontal flow. Relative intensities of this peak oscillatory mode are evaluated through calculation of Q Factor for the corresponding frequency response peak. Frequency and amplitude of peak oscillatory modes are also evaluated. Overall, vertical upflow is seen to exhibit the most significant oscillatory behavior, although in its maximum case amplitude is only seen to be 7.9% of time-averaged module inlet pressure, indicating there is little safety risk posed by oscillations under current operating conditions. Flow visualization image sequences for each orientation are also presented and used to draw parallels between physical characteristics of condensate film behavior under different operating conditions and trends in oscillatory behavior detected in pressure signals.
       
  • Influence of microstructure geometry on pool boiling at superhydrophobic
           surfaces
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Matthew Searle, Preston Emerson, Julie Crockett, Daniel MaynesAbstractPeriodically patterned superhydrophobic surfaces with rectangular rib and circular post arrays were utilized as heat transfer surfaces in a boiling apparatus with the water pool undergoing saturated pool boiling. The surface microstructures were geometrically defined by cavity fraction (the ratio of projected cavity area to surface area), pitch (the center to center distance between microfeatures), and feature height. Surface heat flux and surface superheat, the difference between the heated surface and the pool saturation temperature, were measured for each surface. Ten different micropatterned surfaces with post or rib geometries were considered with cavity fraction varying from 0.5 to 0.98, pitch varying from 8 to 40 μm, and microfeature height at 4 μm or 15 μm. The surface heat flux was measured across a range of surface superheats spanning 2–38 K. It is demonstrated for the first time that the transition from nucleate boiling to film boiling on rib patterned surfaces depends strongly on the cavity fraction. Increasing the microstructure height from 4 μm to 15 μm modestly increases the transition temperature. Nucleate boiling is more suppressed on post patterned surfaces than on rib patterned surfaces. Further, the rib structured surfaces exhibit a sudden transition from nucleate to film boiling while the post structured surfaces exhibit a gradual transition, with the vapor film growing slowly across the surface. Once stable film boiling is reached, the surface microstructure negligibly influences the heat flux for all surfaces.
       
  • Switchable heat transfer in nano Janus-interface-system
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Longyan Zhang, Jinliang Xu, Qicheng Chen, Sheng WangJanus-interface-system is referred as liquid confined between hydrophilic and hydrophobic surfaces, nanoscale energy transfer in Janus-interface-system is not understood. Here, we investigate Poiseuille flow by non-equilibrium molecular dynamics (NEMD) using argon as the working fluid. The two solid walls hold different temperatures and wettabilities. It is found that for pure heat conduction, temperature jumps are negative on hot wall but positive on cold wall to create positive heat flow from hot wall to cold wall (called positive heat transfer). However, the convective energy transfer in Janus-interface-system always behaves positive temperature jumps on the two walls due to viscous heating. We show that, lowering hot wall wettabilities creates more significant velocity and temperature slippages on hot wall than those on cold wall to steepen liquid temperature gradients in nanochannel. We further show that heat flow sign can be switched between positive and negative, by (1) keeping super-hydrophilic hot wall but changing cold wall wettabilities, (2) keeping super-hydrophilic-hot-wall/hydrophobic-cold-wall but varying external forces applied to liquid, and (3) keeping super-hydrophilic-hot-wall/hydrophobic-cold-wall but varying hot wall temperatures. All the three cases yield non-symmetry velocity profile and more sensitive changes of temperature jumps on cold wall than those on hot wall for heat transfer switch. The transition between positive and negative heat transfer occurs at the zero temperature gradient in the channel. The findings not only enhance the understating of nanoscale energy transfer in Janus-interface-system, but also provide novel working principle for nano-devices behaving temperature sensitive nature.Graphical abstractGraphical abstract for this article
       
  • A coupled vaporization model based on temperature/species gradients for
           detailed numerical simulations using conservative level set method
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Min Chai, Kun Luo, Changxiao Shao, Haiou Wang, Jianren FanAbstractThis paper proposes a vaporization model for detailed numerical simulations of a reactive interface. The proposed model represents a preliminary attempt to combine vaporization models based on heat flux and species mass flux to take each model’s advantages concerning numerical accuracy, robustness and applicability. We utilize a conservative level set method to reduce unphysical mass loss in capturing the deformable interface, and the ghost fluid method to accurately impose various jump conditions across the interface. Four validations are conducted to demonstrate both the strengths and limitations of the two original models. Since the vapor mass fraction is relevant in realistic applications, we add the species solver to the heat flux based model and assess the coupling strategy in different situations. The feasibility of switching between the two frameworks in the coupled vaporization model is also demonstrated. Finally, the coupled model is applied to simulations of deformable/moving droplet under high-ambient-temperature conditions. The results of the simulations are consistent with analytical and experimental data. Although additional work is required, the coupled vaporization model exhibits potential as a means for modeling spray combustion.
       
  • Low order modeling method for assessing the temperature of
           multi-perforated plates
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Romain Bizzari, Dorian Lahbib, Antoine Dauptain, Florent Duchaine, Stephane Richard, Franck NicoudAbstractA low-order model is proposed to predict the temperature of a multi-perforated plate from an unresolved adiabatic computation. Its development relies on the analysis of both an adiabatic and a conjugate heat transfer wall resolved large eddy simulation of an academic multi-perforated liner representative of the cooling systems used in combustion chambers of actual aero-engines. These two simulations show that the time averaged velocity field is marginally modified by the coupling with the heat diffusion in the perforated plate when compared to the adiabatic case. This gives rise to a methodology to assess the wall temperature from an unresolved adiabatic computation. It relies on heat transfer coefficients from referenced correlations as well as a mixing temperature relevant to the flow in the injection region where the cold micro-jets mix with the hot outer flow. In this approach, a coarse mesh simulation using an homogeneous adiabatic model for the aerodynamics of the flow with effusion is post-processed to provide a low cost alternative to conjugate heat transfer computations based on hole resolved meshes. The model is validated on an academic test case and successfully applied to a real industrial combustion chamber.
       
  • Two-step method for radiative transfer calculations in a developing pool
           fire at the initial stage of its suppression by a water spray
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Leonid A. Dombrovsky, Siaka Dembele, Jennifer X. Wen, Ivan SikicAbstractA procedure based on two-step method is suggested to simplify time-consuming spectral radiative transfer calculations in open flames containing scattering particles. At the first step of the problem solution, the P1 approximation is used to calculate the divergence of radiative flux, and it is sufficient to determine the flame parameters. The second step of solution is necessary to obtain the radiation field outside the flame, and this can be made independently using the ray-tracing procedure and the transport source function determined at the first step. Such a splitting of the complete problem results in much simpler algorithm than those used traditionally. It has been proved in previous papers that the combined two-step method is sufficiently accurate in diverse engineering applications. At the same time, the computational time decreases in about two orders of magnitude as compared with direct methods. An axisymmetric pool fire at the initial stage of fire suppression by a water spray is considered as the case problem. It is shown that evaporating small water droplets characterised by a strong scattering of infrared radiation are mainly located in regions near the upper front of the flame and one can observe the scattered radiation. This effect can be used in probe experiments for partial validation of transient Computational Fluid Dynamics (CFD) simulations.
       
  • Hybrid lattice Boltzmann finite difference model for simulation of phase
           change in a ternary fluid
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Reza Haghani Hassan Abadi, Mohammad Hassan RahimianAbstractIn this paper, a hybrid lattice Boltzmann finite difference model based on the phase-field lattice Boltzmann and finite difference approaches is proposed to model phase-change phenomena in a ternary system. The system contains three immiscible incompressible fluids and the phase-change process happens at the interfaces of the fluids. Three distribution functions are used in the model; two of which are used to track the interfaces among three fluids and the other one is employed to recover the hydrodynamic properties (pressure and momentum). A sharp-interface energy equation is solved based on a finite difference approach and the net heat flux at the interface is considered as the driving force for the phase-change process. The proposed model is validated against available results and good agreement is found.
       
  • Analysis of representative elementary volume and through-plane regional
           characteristics of carbon-fiber papers: diffusivity, permeability and
           electrical/thermal conductivity
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Pablo A. García-Salaberri, Iryna V. Zenyuk, Andrew D. Shum, Gisuk Hwang, Marcos Vera, Adam Z. Weber, Jeff T. GostickAbstractUnderstanding the transport processes that occur in carbon-fiber papers (CFPs) used in fuel cells, electrolyzers, and metal-air/redox flow batteries is necessary to help predict cell performance and durability, optimize materials and diagnose problems. The most common technique used to model these thin, heterogeneous, anisotropic porous media is the volume-averaged approximation based on the existence of a representative elementary volume (REV). However, the applicability of the continuum hypothesis to these materials has been questioned many times, and the error incurred in the predictions is yet to be quantified. In this work, the existence of a REV in CFPs is assessed in terms of dry effective transport properties: mass diffusivity, permeability and electrical/thermal conductivity. Multiple sub-samples with different widths and thicknesses are examined by combining the lattice Boltzmann method with X-ray tomography images of four uncompressed CFPs. The results show that a meaningful length scale can be defined in the material plane in the order of 1–2 mm, which is comparable to the rib/channel width used in the aforementioned devices. As for the through-plane direction, no distinctive length scale smaller than the thickness can be identified due to the lack of a well-defined separation between pore and volume-averaged scales in these inherently thin heterogeneous materials. The results also show that the highly porous surface region (amounting up to 20% of the thickness) significantly reduces the through-plane electrical/thermal conductivity. Overall, good agreement is found with previous experimental data of virtually uncompressed CFPs when approximately the full thickness is considered.
       
  • Application of indirect non-invasive methods to detect the onset of
           crystallization fouling in a liquid-to-air membrane energy exchanger
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Adesola Oluwasijibomi Olufade, Carey James SimonsonAbstractLiquid-to-air membrane energy exchangers (LAMEEs) use semi-permeable membranes and are designed to transfer heat and moisture between air and liquid streams in heating, ventilating, and air-conditioning (HVAC) systems. However, crystallization fouling in membranes is possible in practical HVAC applications, and this may lead to severe degradation in the performance of LAMEEs.The main aim of this paper is to apply three indirect non-invasive methods to detect the onset of crystallization fouling in a LAMEE. The methods are used to detect fouling by analyzing experimental measurements of moisture flux and moisture transfer resistance. The experimental tests involve dehydrating varying concentrations of MgCl2(aq) desiccant solutions using two types of membrane with different vapor diffusion resistances (VDRs).The results confirm that two of the three methods can effectively detect the onset of crystallization fouling in the LAMEE. Thus, the methods can be used for online monitoring of operating LAMEEs in order to timely identify the initiation of fouling. The results also show that the membrane with a lower VDR produces a higher moisture flux which leads to a higher degree of fouling than the membrane with higher VDR.
       
  • Analysis of temperature oscillations parameters of heat exchanging systems
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Ewa Piotrowska, Piotr SkowrońskiAbstractThe oscillations of temperature in the transient states of heat exchanging systems were investigated. The experiments were carried out using a heat exchanger model. The resistance heating cooper rod was an active side and an element (identical in shape) situated above them, but without contact, was the passive side of the model heat exchanger. During the experiments, the oscillatory character of the changing temperature of the passive element versus the active element was observed. The following parameters of these oscillations were investigated: frequency of free oscillations, damping coefficient and relative damping coefficient. The values of heat flux, distances between elements and their shapes (in pair) were changed and their influence on the parameters of the oscillations were investigated. The value of heat flux has the greatest impact on the values of all the examined oscillation parameters; there is an increase in the value of all the parameters along with the increase in the value of the heat flux. There was no influence of the shape of the element on the values of the investigated parameters. The values of the frequency of free oscillations and the damping coefficient decrease at an increasing distance between them, but the relative damping coefficient increases. These dependencies indicate the complex nature of the studied oscillations.
       
  • Study on analogy principle of overall cooling effectiveness for composite
           cooling structures with impingement and effusion
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Cun-liang Liu, Gang Xie, Rui Wang, Lin YeAbstractThe overall cooling effectiveness, which represents the distribution of dimensionless temperature on gas turbines surface, is an important parameter for conjugate heat transfer analysis of gas turbines. Generally, it is difficult to measure the overall cooling effectiveness in engine condition. However, the overall cooling effectiveness can be measured in the laboratory by matching the appropriate parameters to those in engine condition. Thus, it is important to evaluate the key parameters of matching methods. In this paper, the effects of adiabatic film effectiveness and Biot number on the overall cooling effectiveness were investigated with an impingement/effusion model by numerical simulation, in which 3-D steady RANS approached with the k–ω SST turbulence model was used. The tested plate had 8 cylinder hole rows with 30 degree inclined angle, and the internal cooling employed staggered array jet impingements. The matching performance was evaluated by comparing the results in typical engine condition and laboratory condition. The analogy principles were discussed in detail. The results show that the overall cooling effectiveness can be matched by using suitable matching principle in different lab conditions. The theoretical analysis was verified by numerical results. The distributions and values of overall cooling effectiveness can be matched well between engine condition and lab condition by matching temperature ratio, mainstream side Biot number and blowing ratio. If the temperature ratio is mismatched, the momentum flux ratio will be an important parameter for overall cooling effectiveness, because matching momentum flux ratio can reduce the difference of the adiabatic cooling effectiveness and the heat transfer coefficient ratio between engine condition and laboratory condition.
       
  • Bubble growth model in uniformly superheated binary liquid mixture
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Chang Cai, Hong Liu, Xi Xi, Ming Jia, Hongchao YinAbstractA novel model was developed to investigate the fundamental heat transfer and mass diffusion mechanisms of bubble growth in uniformly superheated ethanol–water mixture. In the proposed model, the energy equation was applied coupling with the quadratic temperature distribution within the thermal boundary layer. The mass diffusion effect was accounted by the introduction of species conservation equation in combination with the quadratic concentration distribution within the concentration boundary layer. Peng-Robinson equation of state and activity coefficient calculation were also adopted for the estimation of vapor-liquid equilibrium. In the present study, the maximum mass diffusion limited growth rate was proposed to quantify and illustrate the effect of mass diffusion on bubble growth. The results show that the bubble growth process in a binary mixture can be divided into three distinctive stages. The later stage of bubble growth is mainly subject to mass diffusion and partly to heat transfer at low ethanol concentrations.
       
  • Study on natural convection characteristics of oil/water emulsions inside
           a rectangular vessel with vertical heating/cooling walls
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Takashi Morimoto, Toshiki Ikeda, Hiroyuki KumanoAbstractEmulsions are mixtures of two immiscible liquids, which are important in various fields such as the food, cosmetics, and pharmaceutical industries. In industrial situations, natural convection may occur inside an emulsion owing to the temperature differences in the emulsion manufacturing and storage processes. Therefore, it is important to understand the natural convection characteristics of an emulsion for effective design of such systems. In the present study, oil-in-water (O/W) emulsions were prepared and the natural convection characteristics of the oil particles of the emulsions inside a rectangular vessel heated from one vertical wall and cooled from the opposite wall were investigated experimentally. Silicone oil was used as the dispersed phase of the O/W emulsion. The test samples were prepared with various oil particle sizes and oil volume fractions. We found that multiple convection layers formed inside the emulsion depending on the wall temperature difference, oil particle size, and oil volume fraction. Furthermore, the Nusselt number of an emulsion with a high oil volume fraction was higher than that of a single-phase fluid.
       
  • Entropy generation of magnetohydrodynamic electroosmotic flow in two-layer
           systems with a layer of non-conducting viscoelastic fluid
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Zhiyong Xie, Yongjun JianAbstractThe entropy generation analysis is investigated in two-fluid dragging systems. The bottom layer fluid is considered as electrolyte solution affected by the applied magnetic field and the upper layer fluid is viewed as non-conducting viscoelastic Phan-Thien-Tanner (PTT) fluid. Under the combined influences of electric and magnetic fields, the upper layer non-conducting PTT fluid can be dragged by the bottom layer fluid due to the interfacial shear stress. Firstly, we obtain the analytical velocity expressions for both bottom layer and upper layer fluids under the unidirectional flow assumption. The bottom layer fluid velocity distribution shows a classical M-type velocity profile. The upper layer fluid flow can be viewed as the plate Couette flow or Couette-Poiseuille flow. Subsequently, the thermal transport characteristic and entropy generation analysis are discussed in the present two-fluid dragging system. The results show that magnetic field can enhance the local entropy generation rate, but viscoelastic physical parameter can restrain the local entropy generation rate. The present theoretical research can be used in the design of thermofluidic device. By manipulating the electric and magnetic fields strength and the ratio of fluid rheological properties, the fluid motion and heat transfer characteristics can be manoeuvred efficiently.
       
  • Numerical analysis and ANFIS modeling for mixed convection of CNT-water
           nanofluid filled branching channel with an annulus and a rotating inner
           surface at the junction
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Fatih Selimefendigil, Hakan F. ÖztopAbstractNumerical study for mixed convection of CNT-water nanofluid flow in a branching channel with annulus at the junction and a rotating surface was performed by using finite volume method. This geometry can be used in a variety of engineering applications such as in geothermal, gas pipelines, in pharmaceutical, fuel cells and many others. The numerical simulations are performed for various values of pertinent parameters such as Richardson number, angular rotational velocity of the inner surface at the annulus junction, solid nanoparticle volume fraction and diameter of the inner rotating. It was observed that the recirculation regions established within the annulus and separated fluid zones on the walls of the branching channel near the junction are strongly influenced by the by rotation of the inner surface at the annulus. The average Nusselt number enhancements up to 64% are obtained for the nanofluid containing the highest particle volume fraction for Ri = 0.01 and Ri = 1 when the inclination angle of the lower branching channel is 45°. Finally, ANFIS modeling technique with triangular-shaped membership function and 48 fuzzy rules are used to predict the average Nusselt numbers for the hot walls of the channel and annulus part.
       
  • Numerical investigation of smoke dynamics in unconfined and confined
           environments
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Chan-Sol Ahn, Boo-Hyoung Bang, Min-Woo Kim, Tae-Gun Kim, Scott C. James, Alexander L. Yarin, Sam S. YoonAbstractBecause of their implications to safety, the study of plume dynamics in high-rise buildings is a research area of interest to building engineers. In this study, the temperature, velocity, and pressure of smoke rising in buildings of various sizes were considered as functions of fire size, and were simulated using the Fire Dynamics Simulator software. Numerical results were validated against the analytical solutions for confined (building enclosure) and unconfined (open-air) systems. As the building area decreased and the fire size increased, buoyancy-driven flow accelerated and the overall building temperature increased. Additionally, the low pressure at the bottom of the building, which resulted from buoyant smoke, increased the vertical pressure gradient throughout the building. These parametric investigations can be used by building engineers concerned with smoke dynamics to develop design-safety guidelines.
       
  • Macrosegregation simulation model based on Lattice-Boltzmann method with
           high computational efficiency
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Munekazu Ohno, Hayato SatoAbstractA macrosegregation simulation model is developed by coupling solute and energy conservation equations with Lattice-Boltzmann Method (LBM), newly developing technique of computational fluid dynamics. Effect of the solidification shrinkage is taken into account in the present LBM as well as effects of the Darcy’s flow and thermos-solutal convection. The present LBM-coupled model is based on modified lattice Bhadnager-Gross-Krook method, the numerical stability of which is better than that of the standard LBM. Accordingly, the present LBM-coupled model can be applied to simulations of macrosegregation behaviors in metallic alloy systems that cannot be handled by the previous LBM-coupled model. The validity of the model was demonstrated by comparing the results for steady-state flows with those of analytical solutions and a conventional model based on the Navier-Stokes equation. In addition, the computational speed of the present model is compared with the one of conventional model in cases of lateral directional solidification of Sn-Bi alloy and continuous casting of a steel slab. It is shown that the present LBM-coupled model enables remarkably faster computation than the conventional model especially in the latter case.
       
  • Experimental and numerical investigations of flow through catalytic
           converters
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Hesham A. Ibrahim, Wael H. Ahmed, Sherif Abdou, Voislav BlagojevicAbstractThe need for improved fuel economy, while meeting more stringent global vehicle emission standards, continues to grow with the increasing demand for environmental protection and rising fuel prices. A new generation of catalytic converters, designed and patented by Vida Fresh Air Corp., offers emissions reduction while improving fuel economy. In this design, a thin layer of insulating material is placed inside the ceramic honeycomb channels, creating a multi-chamber catalytic converter. The improvement in performance of the catalytic converter is attributed to the change in both the flow distribution and the controlled heat diffusion from the inner to the outer chambers. On engine performance tests have shown significant improvements in both fuel economy and emissions, however, the theory of operation of this design needs to be validated for potential design improvements to achieve an optimum performance. In this study both experimental and numerical investigations are carried out in order to understand the flow through the catalytic converter, using different monolith cell densities. A dynamically scaled-down model for a typical flow through catalytic converter was utilized for this study. Detailed experiments were conducted using hot air as the working fluid in order to evaluate the thermal and fluid flow characteristics of the new catalytic converter technology without the effect of chemical reactions. The measurements were performed at a Reynolds number of 43,000 with a free stream temperature of 177 °C. These conditions were selected in order to achieve thermal and hydraulic similarity to actual flow conditions for a typical catalytic converter. Numerical modelling of the flow through the setup under investigation was found to adequately replicate the experimental measurements for temperature, velocity and turbulence intensity within ±3%, ±5% and ±8% respectively. The use of a new design of the catalytic converter found to improve the thermal performance by 18% and the hydraulic performance by 5% without a significant increase of the pressure drop across the catalytic converter.
       
  • Experimental and numerical study of Buoyancy-driven low turbulence flow in
           rectangular enclosure partially filled with isolated solid blockages
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Draco Iyi, Reaz Hasan, Roger PenlingtonAbstractThis paper considers the natural convection inside an air filled enclosure having several isolated cylindrical blockages distributed within it, and arranged parallel to two vertical walls of the enclosure. These two walls are maintained at different temperatures resulting in a natural convection process inside the enclosure. The objectives are to provide experimental temperature data and to investigate the influence of the blockages proximity within and outside the active vertical wall hydrodynamic boundary layer of the natural convection flow and heat transfer. Experiments were designed with high degree of accuracy to provide reliable temperature data-bank for a range of blockages proximity to the active vertical walls. The test enclosure is an air filled rectangular cavity fixed at 0.97 m × 0.4 m × 1 m, corresponding to the height, width and depth respectively. The top and bottom walls are conducting surface and the temperature difference between the active vertical walls was maintained at 42.2 °C resulting in a characteristic Rayleigh number of 4.04 × 109 based on the enclosure height. All the walls of the enclosure were insulated externally while the inner surfaces were covered with conducting plate. The test cavity capability of establishing low turbulence natural convection flows was verified. All temperature data were obtained at steady state and it was verified to be reproducible by repeating the experiment at different times. Also, two-dimensionality was verified via rigorous temperature readings over a period of time. Additional temperature readings were recorded for the air and cylinder surfaces at several distinct locations. Further investigations were conducted using a numerical approach to supplement and validate the experiments.Experimental temperature data collated at various locations within the enclosure show excellent comparison with numerical results and as such provide a useful experimental benchmark temperature data for the validation of low turbulence natural convection flow in enclosure partially filled with isolated solid objects. Our result shows that a significant increment or reduction in air temperature and wall heat transfer could be achieved by varying the blockages proximity, and especially when the blockages are positioned within the hydrodynamic boundary layers of the active vertical walls.
       
  • Direct experimental measurement for partitioning of wall heat flux during
           subcooled flow boiling: Effect of bubble areas of influence factor
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Muritala Alade Amidu, Satbyoul Jung, Hyungdae KimAbstractHeat transfer models in liquid-vapor two-phase flow with wall boiling rely on the wall heat flux partitioning to quantify heat transfer to liquid and vapor separately. Several wall heat flux partitioning models have been proposed over the years based on variety of heat transfer mechanisms, but the three basic mechanisms that form the core of these models are liquid convection, surface quenching and evaporation heat transfer. A key parameter commonly used to determine the relative contribution made by each mechanism is area fraction of influence of bubble which is determined by multiplying maximum bubble projected area fraction with bubble area of influence factor (K). In classic wall heat flux partitioning models, K accounts for the area within which heat is transferred to liquid that moves in towards the heated wall as bubbles lift-off. The value of K has been a subject of controversy over the years with no unanimous conclusion among researchers. Therefore, in this paper, advanced diagnostic approach involving the combination of infrared thermometry and total reflection principle was employed to experimentally study nucleate flow boiling. Rigorous data analyses was performed to partition the wall heat flux into the aforementioned three basic heat transfer mechanisms using different values of K. All three heat transfer mechanisms were significantly sensitive to varying values of K, but setting K = 0.5 with percentage uncertainties of −60%/+50% closely predicted the experimental measurements. In addition, overlapping area of influence due to merging bubbles was observed to be significant in the model at high heat flux condition and must be discounted to get the true bubble area of influence. A correction method for the overlapping area of influence was therefore proposed to enhance accuracy of the predictive model.
       
  • Heat exchange within the partially heated C-shape cavity filled with the
           water based SWCNTs
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Rizwan Ul Haq, Feroz Ahmed Soomro, Z. Hammouch, Sajjad Ur RehmanAbstractIn this article, heat transfer analysis is performed for Magnetohydrodynamic (MHD) water based Single Wall Carbon Nanotubes (SWCNTs) inside a C-shape cavity that is partially heated along the left vertical wall in the presence of magnetic field. The convection inside the cavity due to the temperature difference along the sides of the walls give rise in the temperature and the complete structure is based upon the system of nonlinear coupled partial differential equations. Governing equation are further modified in term of effective thermal conductivity expression that depends upon the radius of nanoparticle and fluid molecule. These equations are solved via Finite Element Method (FEM) utilizing Galerkin approach. The results are presented and analyzed in the form of streamlines, isotherms and Nusselt number for emerging physical parameter, that are, Rayleigh number (104⩽Ra⩽106), Hartmann number (0⩽Ha⩽200) and nanoparticle volume fraction (0⩽ϕ⩽0.2). The study reveals that increase in Rayleigh number enhances the heat transfer rate and increase in magnetic field strength decreases it. For the considered range of nanoparticle volume fraction (0⩽ϕ⩽0.2) have significant impact on the temperature distribution. It is finally concluded that increase in the Rayleigh number enhances the stream flow and isotherms behavior. However, increase in Hartman number decreases the heat transfer rate inside the cavity.
       
  • Supercritical heat transfer characteristics of R1233zd(E) in vertically
           upward flow
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Jiacheng He, Chaobin Dang, Eiji HiharaAbstractThe recently developed low-global-warming-potential working fluid R1233zd(E) is regarded as an alternative to R245fa in the organic Rankine cycle (ORC) considering the environmental impacts. In this study, the heat transfer characteristics of R1233zd(E) at supercritical pressures were investigated experimentally in a vertically upward flow inside a tube. The inner diameter and length of the test tube were 4 mm and 1.04 m, respectively. With the known supercritical heat transfer characteristics of R245fa, the experiment was conducted under the mass fluxes of 400 and 600 kg/m2 s, heat flux from 20 to 80 kW/m2, and pressure of 3.93 and 4.40 MPa, which were equal to the reduced pressure (P/Pcri) of 1.10 and 1.23, respectively. The effects of mass flux, heat flux, and pressure are discussed based on the experimental data. The experimental results are compared with existing correlations and the correlation proposed by Petukhov et al. shows the best predictability. Moreover, a comparison with the heat transfer coefficients of R245fa is presented. For the new R1233zd(E) working fluid, the abrupt deterioration characteristics did not occur under the experimental conditions, and a higher heat transfer coefficient was obtained in the supercritical region, in comparison to that obtained with R245fa.
       
  • Gas-liquid two-phase flow in a square microchannel with chemical mass
           transfer: Flow pattern, void fraction and frictional pressure drop
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Yaran Yin, Chunying Zhu, Rongwei Guo, Taotao Fu, Youguang MaAbstractThe dynamics of the gas-liquid two-phase flow are of great significance for the heat and mass transfer performance in a microreactor. In this paper, the flow pattern, void fraction and frictional pressure drop of gas-liquid two-phase flow of CO2 and MEA/[Bmim][BF4] aqueous solution accompanied by the chemical reaction in a 400 μm square microchannel were investigated experimentally by a high-speed camera and pressure sensor. Three kinds of flow regimes were observed: slug-bubbly flow, slug flow and slug-annular flow. The void fraction and frictional pressure drop in the slug flow regime were mainly investigated, and the applicability of models without consideration of the mass transfer proposed in the literature was assessed. Considering the effect of chemical absorption, two correlations were proposed with the Hatta number for predicting the two-phase void fraction and Chisholm parameter C, which showed good prediction performance.
       
  • An analytical study of the periodic laminar forced convection of
           non-Newtonian nanofluid flow inside an elliptical duct
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Haroun Ragueb, Kacem MansouriAbstractIn this study, an analytical solution was obtained for a laminar forced convection of non-Newtonian nanofluid flowing inside an elliptical duct, with inlet temperature varying periodically with the time. The solution was obtained using the Generalized Integral Transform Technique (GITT). The thermal behavior of Cu-water non-Newtonian nanofluid, described by the power-law model was investigated. Also, an accurate correlation was established to estimate the thermal length required to achieve 99% of the amplitude attenuation. The results show a significant effect of aspect ratio β/α and fluid behavior index on the temperature amplitude reduction. For instance, an elliptical duct with β/α = 0.25 reduces the thermal length Lth more than 50% compared with circular duct. Adding nanoparticles until 5% increases the heat transfer coefficient up to 27% for the cylindrical tube. Besides, the heat transfer coefficient is improved over 42% relatively to the cylindrical configuration by reducing the aspect ratio to 0.25. Therefore, adding 5% of nanoparticles both using an elliptical duct with β/α = 0.25, improves the mean heat transfer coefficient around 83% compared to the flow of water base fluid inside a cylindrical duct.
       
  • A novel method for determining the melting point, fusion latent heat,
           
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Xiao-Hu Yang, Jing LiuIn this paper, a novel method for determining the main thermophysical properties of phase change materials (PCM) is proposed, which can be called as “T-melting CHF” method. The melting point, fusion latent heat, thermal conductivity, and specific heat capacity in both solid and liquid phase of PCM, can all be obtained simultaneously by only one test. The theoretical fundamentals lying behind are introduced, the measurement apparatus and measurement principles are presented, and corresponding restrictive conditions for high accuracy measurement are provided. Theoretically, the thermophysical properties can be accurately measured by the proposed method if the test module can be perfectly insulated. However, heat loss inevitably exists in practical measurement, it will significantly influence the measuring accuracy, hence a correction method is proposed to improve this situation. A typical low melting point metal (gallium) and a typical organic PCM (n-eicosane) were tested to verify the feasibility and accuracy of the method. The experimental results agree well with the reference data reported in the literature. Compared with conventional measurement techniques, the method proposed here has advantages such as simple structure, low cost and high measurement speed; more importantly, it is able to measure multiple properties simultaneously.Graphical abstractGraphical abstract for this article
       
  • Numerical and experimental investigation on the reactant gas crossover in
           a PEM fuel cell
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Nguyen The Truc, Shun Ito, Kazuyoshi FushinobuAbstractGas crossover through the membrane is one of the key factors for membrane degradation and performance loss of proton exchange membrane fuel cell (PEMFC). The permeation of hydrogen and oxygen through the membrane are consumed with the generation of heat and water but without the generating of useful work, leading to a fuel inefficiency. On the other hand, hydrogen peroxide (H2O2) is most probably formed by the reaction of crossover hydrogen and oxygen at both the anode and cathode side. In addition, the chemical reaction of gas crossover can produce peroxide (HO) and hydroperoxide (HOO) radicals, which could accelerate the membrane degradation. In this study, a numerical simulation model has been built using the partial differential equation solver FreeFem++. A steady-state, two-dimensional, single-phase and non-isothermal model of a single PEMFC has been considered to determine the water content distribution, temperature profile, and permeation of gaseous species within the membrane. An in-situ microprobe technique has been also applied to determine the properties of the oxygen crossover with a range of relevant fuel cell operating temperatures and reactant humidity. The numerical results are compared with experimental data of the diffusion coefficient of reactants gases in the membrane, in order to investigate the gaseous species transport characteristics in the membrane at very low current density.
       
  • Use of vapochromic crystals to measure the concentration of a gaseous
           throughflow at the solid-fluid interface
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): C.M. Sangan, O.J. Pountney, J.A. Scobie, B. Cochrane, C. Stubbs, P.R. RaithbyAbstractThis paper demonstrates the potential of vapochromic crystals as a sensing medium for measurements of local species concentration. Vapochromic crystals exhibit a reversible colour change based on the adsorption and desorption of water. As the water content of the crystals changes so too does the wavelength of light that they reflect (i.e. they change colour). In the situation where humid air mixes with a dry gas, the resulting specific humidity of the mixture can be related to the concentration level of the dry gas through a simple mass balance. As far as the authors are aware, this is the first time that vapochromic crystals have been used in this context.A number of the factors that affect the colour change of the crystal are investigated through simple flat plate experiments in a small wind tunnel. In all experiments, the hue and intensity of the vapochromic crystal was measured as a function of local dry gas concentration; in this case CO2. Green intensity levels exhibited the broadest activity over the widest range of CO2 levels, and was therefore used to quantify concentration.The crystals demonstrated a pronounced hysteresis, where the adsorption and desorption of water into the crystal structure was shown to occur at different concentration levels. The transition band was also shown to be highly temperature dependent when tested over a range of 22–44 °C. The vapochromic crystals were assessed for repeatability and found to sense the local CO2 concentration to ±1.5% CO2 over a range of green intensity values from 90 to 170. A practical example is presented to show how vapochromic crystals could be applied to the mixing of fluid streams in gas turbine film cooling.
       
  • Regulation of gas-liquid stratified flow boiling dynamic instabilities in
           horizontal tube: Effects of heat load distribution and wall thermal
           capacity
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Liang Zhang, Yufei Wang, Zitao YuAbstractIn this work, an experimental investigation on the regulation of gas-liquid stratified flow boiling dynamic instabilities was carried out in a 1530 mm long horizontal arranged copper tube with an inner diameter of 12 mm. Two different thermal boundary conditions, namely (i) heat load distribution, (ii) wall thermal capacity were investigated. Three different heat load distributions (uniform heating, power decrease and power increase) and three kinds of tube with different thickness of graphite casing tubes (bare, 6 mm and 12 mm) were analyzed, respectively. The results showed that the oscillation intensity of gas-liquid stratified flow boiling dynamic instabilities was highly related to occurrence of the onset of nucleating boiling (ONB). In comparison with the based cases, the power increase heat load condition especially that with lower inlet subcooling degree and the case with thicker graphite casing tube had delayed the occurrence of ONB. And finally a suppression of dynamic instabilities was obtained. On the contrary, an early occurrence of ONB and an enhancement of gas-liquid stratified flow boiling instability were obtained for the other two cases.
       
  • Transient heat transfer characteristics of array-jet impingement on
           high-temperature flat plate at low jet-to-plate distances
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Keqian Zhu, Pingping Yu, Ningyi Yuan, Jianning DingAbstractNumerical studies on the transient heat transfer characteristics of air-array-jet impingement, for small jet-to-plate distances and a large temperature difference between the nozzle and plate, are presented. The total mass flow rate of the jets (ṁ) is constant at 30.34 kg/h. The nondimensional jet-to-plate distance (H/D) for a nozzle diameter (D) of 5 mm is varied from 0.2 to 1. The nondimensional hole-to-hole spacing is S/D = 5, 7, and 10, respectively. The variations in the transient heat transfer characteristics and flow velocity at different values of H/D and S/D, as a function of the cooling time, are discussed. It is found that there exists a turning point H/D = 0.4 in the effect of the transient heat transfer. As H/D is decreased, the quenching time shrinks quickly. The velocity field is proposed as an explanation for the observed transient heat transfer. In addition, an appropriate proposal is presented for designing equipments of tempering ultra-thin glass.
       
  • Investment casting and experimental testing of heat sinks designed by
           topology optimization
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Tian Lei, Joe Alexandersen, Boyan S. Lazarov, Fengwen Wang, Jan H.K. Haertel, Salvatore De Angelis, Simone Sanna, Ole Sigmund, Kurt EngelbrechtTopology optimization (TO) is an attractive numerical tool to obtain optimized engineering designs, which has been originally developed for mechanical optimization and extended to the area of conjugate heat transfer. With rapid developments in topology optimization models, promising designs have been proposed and presented recently for conjugate heat transfer problems. However, only a very small number of experimental validations of TO heat transfer devices have been reported. In this paper, investment casting (IC) using 3D stereolithography (SLA) printed patterns is proposed to fabricate 3D metal heat transfer devices designed by TO. Three heat sinks for natural convection are designed by a previously reported topology optimization model and five reference pin-fin heat sinks are devised for comparison. From those designs six heat sinks are cast in Britannia metal, fully reproducing the complex 3D optimized designs. It shows that SLA-assisted IC is a very promising technology with low cost and high accuracy for fabricating TO metal parts, which is not limited to heat transfer devices and can be extended to other areas such as structural optimization. A natural convection experimental setup is used to experimentally study the performance of the fabricated heat sinks. The results show that the tested TO heat sinks can always realize the best heat dissipation performance compared to pin-fin heat sinks, when operating under the conditions used for the optimization. Moreover, validation simulations have been conducted to investigate the temperature distribution, fluid flow pattern and local heat transfer coefficient for the TO and pin-fin designs, further evidencing that TO designs always perform better under the design conditions. In addition, the impact of heat sink orientation and radiation are presented.Graphical abstractGraphical abstract for this article
       
  • Investigation of temperature behavior for multi-fractured horizontal well
           in low-permeability gas reservoir
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Hongwen Luo, Haitao Li, Yahui Li, Yu Lu, Yongsheng TanAbstractThis study aims to interpret the temperature behavior of a cemented multi-fractured horizontal well (MFHW) in a low-permeability gas reservoir (LPGR) during production. First, considering heat conduction, heat convection, thermal expansion, viscous dissipation, and the Joule–Thomson effect, a comprehensive numerical temperature prediction model is developed under a single-phase condition. The developed models are formulated for the reservoir and wellbore domains based on mass, momentum, and energy conservation. The non-Darcy law is applied to the numerical models, and radial flow in the hydraulic fractures is accounted for when the reservoir and wellbore models are coupled. These developed models are solved numerically by the finite difference method. Then, synthetic cases demonstrate the models’ ability to predict the temperature behavior and clarify the change regularity of the wellbore temperature profile for an MFHW in an LPGR. The effects of pressure interference among hydraulic fractures on the inflow rate are analyzed. Based on the sensitivity of arriving temperature to the fracture parameters, an approach to plotting fracture parameter diagnosis charts are introduced. In addition, a field case is provided to illustrate the application and feasibility of the new models on the basis of the accurate simulated results of wellbore temperature profiles.
       
  • A numerical study of forced convection from an isothermal cylinder
           performing rotational oscillations in a uniform stream
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): H.V.R. Mittal, Qasem M. Al-MdallalAbstractForced convection from a heated rotationally oscillating circular cylinder placed in a uniform cross flow of constant properties fluid is investigated. The two-dimensional governing equations of flow motion and energy are solved numerically on non-uniform polar grids using a higher order compact (HOC) formulation. The flow and thermal fields are mainly influenced by Reynolds number, Re, Prandtl number, Pr, maximum angular velocity of the cylinder, αm, and the frequency ratio, f/f0, which represents the ratio between the oscillation frequency, f, and the natural vortex shedding frequency, f0. The numerical simulations are performed at Re=200,Pr=0.5-1.0,αm∈[0.5,4.0] and f/f0∈[0.5,3.0]. The resulting lock-on phenomena behind the cylinder is detected and thermal field is determined. Comparisons with previous numerical and experimental results verify the accuracy and the reliability of the present study. Variations in heat transfer coefficients within the lock-on ranges are investigated to build a connection between the heat transfer and the lock-on regimes.
       
  • Adsorption of Difluoromethane (HFC-32) onto phenol resin based adsorbent:
           Theory and experiments
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Muhammad Sultan, Takahiko Miyazaki, Bidyut B. Saha, Shigeru Koyama, Hyun-Sig Kil, Koji Nakabayashi, Jin Miyawaki, Seong-Ho YoonAbstractAdsorption and desorption of difluoromethane (HFC-32) onto newly developed phenol resin based adsorbent (SAC-2) have been measured experimentally for the isotherm temperatures ranging from 30 °C to 130 °C and pressure up to 3 MPa. A magnetic suspension balance based adsorption measurement unit is used to measure adsorption uptake gravimetrically. The presented SAC-2/HFC-32 pair has adsorption uptake as high as 2.23 kgref/kgads (excess adsorption) and 2.34 kgref/kgads (absolute adsorption) at 30 °C and 1.67 MPa. To the best of our knowledge, it is the highest HFC-32 adsorption capacity onto any adsorbent available in the literature. The experimental data of adsorption/desorption isotherms show that there is no hysteresis for the studied pair. The data have been fitted with Tóth; Dubinin–Astakhov (D–A); and Guggenheim, Anderson, De-Boer (GAB) adsorption isotherm models. The parameters of adsorption isotherm models are optimized by nonlinear optimization technique. The D–A model fits the experimental data precisely as compared to other models. In addition, numerical values of isosteric heat of adsorption have also been extracted by means of Clausius–Clapeyron equation using adsorption isotherm models.
       
  • Transient model of carbon dioxide desublimation from nitrogen-carbon
           dioxide gas mixture
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Y.N. Wang, J.M. Pfotenhauer, X.Q. Zhi, L.M. Qiu, J.F. LiAbstractCarbon dioxide (CO2) cryogenic desublimation separation has become an emerging carbon capture method in recent years due to its advantages of a contamination-free process and compactness. So far, there have been few research works on revealing the detailed desublimation characteristics of CO2 associated with the flow as well as mass and energy conservation in the practical cryogenic CO2 capture process. In this study, a transient model for analyzing the CO2 cryogenic desublimating in mixture gas is proposed. The model contains a tube-in-tube counter-flow heat exchanger including three control volumes, the nitrogen (or helium) coolant, the wall with the solid CO2 layer and the mixture. The deposition distribution, capture rate and energy consumption of the dynamic desublimation process under different operation conditions are investigated. The model is verified by some experiment results. Results show that an improved modeling accuracy is obtained by taking the solid CO2 layer into consideration. During the dynamic desublimation process, the deposition rate is the highest near the inlet of gas mixture due to the high mass diffusion there, and a low energy consumption will be obtained at high concentration and low flow velocity of CO2 supply. The theoretical method here provides better understanding of the CO2 desublimation features in annular tube, which will be helpful for conducting an efficient CO2 capture process.
       
  • Capillary dynamic under nanoconfinement: Coupling the energy dissipation
           of contact line and confined water
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Dong Feng, Xiangfang Li, Keliu Wu, Jing Li, Wen ZhaoAbstractUnderstanding the dynamic imbibition behaviors through nanopores is a subject of great interest in many fields. Recent molecular dynamics (MD) simulations and pressure-driven experiments demonstrated the increased flow resistance of nanoconfined water, which proposed a challenge to the classical molecular kinetic theory (MKT) that the friction dissipation mainly occurs at the three-phase contact line (TPCL) during the dynamic imbibition process. To address this issue, a unified model that combines the friction of moving contact line and confined water behind the meniscus is proposed to capture the dynamic imbibition behaviors at the nanoscale. The model is successfully validated against the published literatures. The results demonstrate that (1) the friction of confined water in hydrophilic silica nanopores (
       
  • An analytical model for shale gas transport in circular tube pores
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Shouceng Tian, Tianyu Wang, Gensheng Li, Mao Sheng, Qingling Liu, Shikun ZhangAbstractAn analytical model for gas transport in shale media is proposed on the basis of the weighted superposition of slip flow, bulk diffusion and Knudsen diffusion. The model takes account of slip effect and real gas effect, and is successfully validated by experimental data and Lattice Boltzmann simulation results. The contribution of each transport mechanism to the total flow is investigated. The effect of porosity, diameter and pressure on the apparent permeability is studied and a sensitivity analysis is performed to evaluate the significance of the parameters for gas transport. The results show: (1) the present model can reasonably describe the process of the mass transform of all different gas transport mechanisms; (2) As pressure and pore diameter decrease, the number of molecule-wall collisions gradually predominates over the number of intermolecular collisions, Knudsen diffusion contributes more to the total flow; and (3) the apparent permeability increases with porosity, pore diameter, and decreases with pressure. It is more sensitive to pressure in rarefied gas flow regime, and pore diameter has a significant impact under high pressure. The present model can provide some theoretical support in numerical simulation of shale gas production.
       
  • Uncertainty quantification in non-equilibrium molecular dynamics
           simulations of thermal transport
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Manav Vohra, Ali Yousefzadi Nobakht, Seungha Shin, Sankaran MahadevanAbstractBulk thermal conductivity estimates based on predictions from non-equilibrium molecular dynamics (NEMD) using the so-called direct method are known to be severely under-predicted since finite simulation length-scales are unable to mimic bulk transport. Moreover, subjecting the system to a temperature gradient by means of thermostatting tends to impact phonon transport adversely. Additionally, NEMD predictions are tightly coupled with the choice of the inter-atomic potential and the underlying values associated with its parameters. In the case of silicon (Si), nominal estimates of the Stillinger-Weber (SW) potential parameters are largely based on a constrained regression approach aimed at agreement with experimental data while ensuring structural stability. However, this approach has its shortcomings and it may not be ideal to use the same set of parameters to study a wide variety of Si-based systems subjected to different thermodynamic conditions. In this study, NEMD simulations are performed on a Si bar to investigate the impact of bar-length, and the applied temperature gradient on the discrepancy between predictions and the available measurement for bulk thermal conductivity at 300 K by constructing statistical response surfaces at different temperatures. The approach helps quantify the discrepancy, observed to be largely dependent on the system-size, with minimal computational effort. A computationally efficient approach based on derivative-based sensitivity measures to construct a reduced-order polynomial chaos surrogate for NEMD predictions is also presented. The surrogate is used to perform parametric sensitivity analysis, forward propagation of the uncertainty, and calibration of the important SW potential parameters in a Bayesian setting. It is found that only two (out of seven) parameters contribute significantly to the uncertainty in bulk thermal conductivity estimates for Si.
       
  • An internal penalty discontinuous Galerkin method for simulating a
           thermoelectric cooler
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Zhemin Cai, Ben ThornberAbstractCompact modelling of a thermoelectric cooler in the computational fluid dynamics approach is essential for reliable product design in the telecommunication industry, particularly for the package design of the optical laser or the wavelength selective switch. When simulating these fluid thermal structure interaction problems numerically, stability and high order of accuracy are required to capture all of the necessary physics. The principle benefit of using the discontinuous Galerkin (DG) method is that it can produce a high order accurate scheme which can achieve an equivalent error compared to the lower order scheme with orders of magnitude lower computational effort. Based on the recent development of a framework for the computation of fluid thermal structure interaction problems within multi-solid domains using DG methods on unstructured grids([1,2]) ; this paper has proposed a detailed compact thermoelectric cooler (TEC) modelling method based on an existing black box like compact TEC model [4]. Close comparisons validate that both the detailed and the black box like compact model are accurate enough to simulate the conduction only case. When air convection is required to carry out a system-level thermal management optimization, the detailed compact modelling method is more reliable than the black box like compact TEC model. Furthermore, the thermal expansion of an operating TEC has been examined. Compared to the black box like compact TEC model, the simulation results of the detailed compact method have better agreement with electronic speckle pattern interferometry data.
       
  • Heat transfer behavior of elemental sulfur for low temperature thermal
           energy storage applications
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): K. Nithyanandam, A. Barde, R.E. WirzAbstractElemental sulfur provides a low-cost, high-performance thermal storage option for a wide range of applications and over an exceptionally wide range of temperatures (50 °C to over 600 °C). In previous efforts we have shown impressive performance for 200–600 °C, while in this study we examine the low-temperature (50–200 °C) thermal charge and discharge behavior of isochoric sulfur-based storage using a detailed computational model solving for the conjugate heat transfer and solid-liquid phase change dynamics. The model provides excellent agreement with experimental results. We show that sulfur exhibits lower viscosity because of reduction in the chain-length of polymeric sulfur caused by trace amounts of organic substances resulting in attractive charge and discharge performance. The results from the parametric analysis of pipe diameter on the charge and discharge heat transfer characteristics are used to develop a simple, generalized correlation that relates the transient sulfur temperature and liquid fraction evolution as a function of dynamically evolving buoyancy-Fourier number due to the solid-liquid phase change. This solid-liquid buoyancy-Fourier, BFs-l, correlation can be used for effectively designing sulfur-based thermal energy storage systems for transient operation in low temperature applications.
       
  • A modified buoyancy effect correction method on turbulent convection heat
           transfer of supercritical pressure fluid based on RANS model
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Pei-Xue Jiang, Zhen-Chuan Wang, Rui-Na XuAbstractThe performance of the turbulent flow model for predicting the buoyancy effect on convective heat transfer of supercritical fluid is severely affected by strongly varying thermal physical properties near the pseudo-critical point. Over-prediction is attributed, at least partly, to the misuse of the constantly turbulent Prandtl number for the turbulent heat flux in the turbulence model. A method that considers the anisotropic turbulent heat flux has been proposed to improve the prediction accuracy of numerical simulation. A buoyancy effect model that accounts for the production of turbulent kinetic energy and a turbulent Prandtl number model accounting for turbulent thermal diffusion, which are both based on the anisotropic turbulent heat flux model, was adopted in the original AKN k-ε model. Experimental results and direct numerical simulations (DNS) data were used to validate the performance of the “Modified model.” The “Modified model” produced accurate predictions for all heat transfer deterioration cases examined in the present paper. The buoyancy effect model reflects the basic mechanism of heat transfer deterioration and recovery due to accurate predictions of turbulent kinetic energy. The value of Prt in the buffer layer obtained with the turbulent Prandtl number model is essential for accurate reproductions of experimental data.
       
  • Heat transfer enhancement strategies in a swirl flow minichannel heat sink
           based on hydrodynamic receptivity
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Benjamín Herrmann-Priesnitz, Williams R. Calderón-Muñoz, Gerardo Diaz, Rodrigo SotoAbstractThe swirl flow minichannel heat sink has shown to be a promising alternative for thermal management of high heat flux applications, such as electronics and concentrated photovoltaics. Effective heat transfer enhancement strategies for this device are identified by studying the receptivity of temperature disturbances to a momentum forcing input. Steady state laminar flow is calculated numerically and experimental measurements are carried out to validate the results for subcritical Reynolds numbers. Using the framework of nonmodal stability theory, a harmonically driven linear perturbation problem is formulated, and the methodology to apply the local and parallel flow approximations based on order of magnitude arguments is detailed. The input-output response of temperature perturbations to forcing of the radial, azimuthal, and wall-normal momentum components is calculated for a range of wavenumbers, waveangles and temporal frequencies. The largest amplification is presented by streamwise vortices and streaks, followed by axisymmetric inward travelling waves, and then by streamwise propagating waves. Micromachining the channel walls with streamwise spiral grooves is proposed as a heat transfer enhancement technique. Excitation of streamwise independent structures in the wall-normal direction is expected, therefore maximum amplification should be obtained. Due to its simple implementation, we also propose using a pulsating flow rate as a heat transfer enhancement technique. Receptivity results for streamwise propagating waves of radial forcing show a response curve with moderate amplification for a wide range of actuation frequencies. Experimental work is conducted to measure the performance of the swirl flow channel heat sink using flow pulsations at the range of forcing frequencies suggested by the receptivity study. Compared to the unforced case, a lower wall temperature (up to 5°C cooler) was observed with pulsations, at the same imposed heat flux and flow rate. To get the same wall temperature as in the unforced case, a pumping power reduction of up to 26.6% was observed, and using the same pumping power resulted in up to a 10.3% Nusselt enhancement. Hydrodynamic receptivity was successfully used to identify effective heat transfer enhancement strategies, resulting in a significant performance improvement for the swirl flow channel heat sink. This physics based approach can be extended to other techniques, for instance, to select the wavelength of a wavy surface, the periodicity of surface roughness elements, or the frequency of acoustic vibrations.
       
  • Direct numerical simulation study of end effects and D/d ratio on mass
           transfer in packed beds
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Shivkumar Bale, Shashank Tiwari, Mayur Sathe, Abdallah S. Berrouk, Krishnaswamy Nandakumar, Jyeshtharaj JoshiAbstractDirect Numerical Simulation (DNS) was performed to investigate the end effects on mass transfer in a packed bed for Reynolds number (Re) ≤ 100. The system considered in this study was naphthalene-air with a Schmidt number (Sc) ∼ 2.52. The location of the spheres’ centers in a randomly packed bed were obtained from Discrete Element Method – Computational Fluid Dynamics (DEM-CFD) simulations. The influence of the confining wall on how packed bed ends affect mass transfer was studied by examining the axial void fraction profile with varying ratio of the column diameter to the particle sphere diameter (D/d). Overall, it was found that the confining wall has a significant impact. The ‘local’ mass transfer coefficient was calculated based on the obtained DNS results and the probability distribution curve and the spatial distribution of the computed ‘local’ Sherwood numbers as function of the ratio X/L (ratio of the height of the active part of the bed to the total height of the bed) were developed to quantify the end effects on mass transfer within packed beds. For a packed bed with no wall effects (D/d = 11), it was found that the end effects can be eliminated by replacing the active particles located at ∼2 sphere diameters from the entrance and ∼1 sphere diameter from the exit by inert particles.
       
  • High-throughput transient thermal interface testing method using
           time-domain thermal response
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Menglong Hao, Timothy S. FisherAbstractIn the field of thermal interface testing, the one-dimensional (1D) reference bar method has been the most popular and trusted among many available techniques. However, this steady-state method has several drawbacks, including low test speed and inability to capture dynamic response. In this paper, we report a high-throughput transient method that can be used in concert with the traditional 1D reference bar setup without hardware modifications. Instead of waiting for steady-state conditions, the method requires only an arbitrary segment of the transient thermal response in the time domain. The transient thermal model and data fitting algorithm are presented. Radiation heat loss and temperature-dependent thermophysical properties are incorporated in the model to improve high-temperature accuracy. The measurement uncertainty is quantified numerically, and the criteria for choosing the input segment are discussed. The effects of the TIM (thermal interface material) heat capacity are also investigated, and reveal that in most practical cases, the measurement result is not sensitive to the heat capacity of the TIM. In the end, we demonstrate this method on a commercial TIM sample over a wide temperature range (room temperature to 400 °C) and show that the results are comparable to those obtained from a steady-state method but with drastically reduced testing time.
       
  • Condensation heat transfer and pressure drop of refrigerants HFO-1234yf
           and HFC-134a in small circular tube
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Chien-Yuh Yang, Hamid NalbandianAbstractHFO-1234yf has similar thermodynamic properties to HFC-134a but much lower GWP value. It is expected as a good candidate to replace the refrigerant HFC-134a in the near future. However, only very few papers have been published in the past years regarding to the flow condensation heat transfer performance of this new refrigerant. This study provides an experimental analysis of flow condensation heat transfer and pressure drops of refrigerants HFO-1234yf and HFC-134a in a small circular tube. The test results show that both pressure drop and condensation heat transfer performance depend on the fluid properties, flow conditions and flow patterns. The major controlling properties on pressure drops and heat transfer coefficients is strongly depending on their two-phase flow pattern at various flow conditions. At the lowest mass velocity, gravity is the major force that dominates the heat transfer mechanism and the flow pattern is slug. Higher liquid viscosity retarded the condensate flow but higher liquid conductivity provided better heat transfer through the liquid film. Both liquid viscosity and conductivity are the important controlling properties. While mass velocity and vapor quality increased, the effect of shear force increased and the flow pattern transferred to annular. Liquid thermal conductivity became the major controlling property at high vapor qualities. But at low vapor qualities, gravity is still important and therefore liquid viscosity is one the major controlling parameter. At the highest mass velocity conditions, gravity effect is negligible even though at very low vapor quality condition. Shear force dominated the condensation heat transfer mechanism and liquid conductivity is the most important controlling property. It can be concluded that the flow condensation heat transfer performance is strongly depending on the two-phase flow patterns at various flow conditions.
       
  • Direct-coupled desorption for small capacity ammonia-water absorption
           systems
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Marcel A. Staedter, Srinivas GarimellaAbstractAn investigation of direct gas-coupled desorption for small capacity ammonia-water absorption is presented. Some applications favor or require the use of direct-coupling of the heat source for desorption; therefore, a systematic treatment of this topic is needed for the optimal design of small-capacity absorption systems. Gas-coupled desorption is accomplished through diabatic distillation, and an optimal gas side geometry is established. Gas side optimization considers pressure drop minimization as well as geometric constraints such as column diameter and number of gas tubes. A heat and mass transfer model is developed and validated with experiments. Excellent internal vapor purification is achieved and the results agree well with the heat transfer and pressure drop predictions. These results demonstrate the applicability of direct-coupled desorption to small-capacity ammonia-water absorption systems. A comparative assessment with indirect-coupled desorption components is also made.
       
  • Subcooling effect on boiling heat transfer of inclined downward-facing
           surface under low flow and pressure
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Uiju Jeong, Sung Joong KimAbstractThe present study investigated the physical processes responsible for the variation in the boiling curve and critical heat flux (CHF) caused by liquid subcooling under atmospheric pressure in a rectangular flow channel; the flow channel was oriented 10° upward from the horizon. Bubble dynamics were examined using a high-speed camera and optical fiber microprobes. A solid copper block was utilized as a test heater and mounted above the flow channel to simulate the passive cooling system of an ex-vessel core catcher designed for nuclear power plants. Low mass flux and subcooling conditions ranging from 40–300 kg/m2 s and 5–25 K, respectively, were applied at the inlet of the test section. At the mass flux value of 40 kg/m2 s, large sliding bubbles were attributed to a key criterion for enhanced boiling heat transfer when the liquid subcooling was varied up to 15 K. The results showed that the CHF was weakly dependent on the degree of liquid subcooling, which deviates from the general trend reported by many researchers. A repetitive flow reversal along with a pressure shock appeared, owing to the rapid condensation at the exit, which added complexity to the analysis of the CHF. This study provides physical insights for understanding the subcooled flow boiling heat transfer mechanism (including the CHF) based on sophisticated experimental measurements, such as the visual capture of boiling dynamics using high-speed video and local void fraction.
       
  • Influence of the noncondensable component on the characteristics of
           temperature change and the intensity of water droplet evaporation
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Vladimir Yu. Levashov, Alexei P. Kryukov, Irina N. ShishkovaAbstractThe removal of vapor molecules from a droplet surface is an important stage of evaporation in a vapor–gas mixture. In this work, with the evaporation of a water droplet in a vapor–gas medium as the example, the influence of the noncondensable component on the intensity of the evaporation process and the characteristics of the temperature change is examined. The heat supplied to an interface is often assumed to be entirely utilized for evaporation, with the formed vapor removed from the evaporation surface through diffusion. However, the diffusion flux develops at a distance of some mean free paths of vapor molecules away from the evaporation surface, that is, in the Knudsen layer. In this layer, because of intermolecular collisions, the molecule–velocity distribution undergoes substantial changes, which are calculated using the methods of physical kinetics. Herein, the system of two Boltzmann kinetic equations for a vapor–gas mixture is used for calculating mass flux density of the evaporating substance near the evaporation surface. The calculation results are then compared with published experimental data.
       
  • Heat transfer analysis of methane hydrate dissociation by depressurization
           and thermal stimulation
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Qing-Cui Wan, Hu Si, Bo Li, Gang LiAbstractThe dissociation of natural gas hydrate is an endothermic reaction closely related with the heat transfer characteristics in porous media. This study mainly focuses on the three-dimensional heat transfer behaviors during hydrate dissociation by depressurization and thermal stimulation based on the experiments in a Cuboid Pressure Vessel (CPV). The evolution of various heat flows (including the heat transferred from the boundaries QB, the injected heat from the well Qinj, the heat consumed by the hydrate dissociation QH, and the sensible heat change of the deposit QS) and their relationships during hydrate dissociation are obtained through numerical simulation. The heat loss QL during gas production is calculated and analyzed for the first time. It is found that the hydrate dissociation is mainly promoted by the driving forces of depressurization (Fdep) and thermal stimulation (Fths), which are dependent on the heat flows of QB and Qinj, respectively. The effect of Fdep will be weakened under higher Fths. Part of Qinj and QB are absorbed and stored as QS by the porous media and the fluids of the deposit. Once QB becomes negative, it starts to make contribution to the heat loss instead of the hydrate dissociation, resulting in a sharp increase of QL. In addition, a proper thermal stimulation rate q and production pressure PW should be selected so that the hydrate dissociation rate could be significantly enhanced while the thermal efficiency and energy efficiency are still favorable when compared with using single depressurization.
       
  • Research on macroscopic and microscopic heat transfer mechanisms based on
           non-Fourier constitutive model
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Lin Liu, Liancun Zheng, Fawang LiuAbstractBased on the Cattaneo-Christov model and dual-phase-lag model, a novel constitutive model is proposed to study macroscopic and microscopic heat transfer mechanisms in the moving media. Formulated governing equation contains relaxation parameters and time fractional derivative with the highest order of 1 + α (0 
       
  • Experimental and numerical study on the regeneration performance of LiCl
           solution with surfactant and nanoparticles
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Tao Wen, Lin Lu, Hong Zhong, Chuanshuai DongAbstractThe paper experimentally and numerically investigated the enhancement of LiCl falling film regeneration performance in a plate type regenerator by adding surfactant polyvinyl pyrrolidone (PVP) and multi-walled carbon nanotubes (MWNTs). Experimentally, by adding surfactant PVP and adopting mechanical methods, steady nanofluid containing MWNTs was successfully fabricated. The regeneration characteristics of LiCl/H2O solution, LiCl/H2O-PVP solution and LiCl/H2O-MWNTs nanofluid were identified quantitatively. Compared with the regeneration rate of the LiCl/H2O solution, the values of the LiCl/H2O-PVP solution and nanofluid are on average 24.9% and 24.7% greater. These enhancements can be attributed to the increase of mass transfer area and decrease of falling film thickness, which is caused by a decrease in contact angles. However, adding 0.1 wt% MWNTs to the LiCl/H2O-PVP solution has negligible influence on the regeneration rate. The three solutions have nearly the same mass transfer coefficients under comparable operating conditions. Theoretically, a mathematical model was built with the consideration of film contraction to describe the simultaneous heat and mass transfer processes in the regenerator. The calculated falling film wetting areas agree well with the measured ones, with a relative difference of less than 6%. The mean absolute relative deviation between the computational regeneration rates and experimental ones for the LiCl/H2O solution, LiCl/H2O-PVP solution and LiCl/H2O-MWNTs nanofluid are 9.01%, 3.95% and 4.22%, respectively, which demonstrates the accuracy of the developed model. The experimental data and newly developed numerical model are helpful for the study of regeneration enhancement and system design of liquid desiccant cooling systems.
       
  • Experimental investigation on Al2O3-R123 nanorefrigerant heat transfer
           performances in evaporator based on organic Rankine cycle
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Feng Jiang, Jialing Zhu, Guanglei XinThis paper presents an experimental investigation of variation tendency of heat transfer coefficient, log-mean temperature difference and differential pressure of pure R123 and 20 nm Al2O3-R123 nanorefrigerants with four various volume concentrations, 0.03%, 0.13%, 0.18%, 0.23% flowing inside the evaporator of organic Rankine cycle system under the conditions of various heat source temperatures and flow rates. Heat source temperatures are in the range of 50–90 °C at an interval of 10 °C, and heat source flow rates are 0.7 m3/h, 1.3 m3/h and 1.8 m3/h. Results show an increment of heat transfer coefficient along flowing direction for both pure R123 and four Al2O3-R123 nanorefrigerants with the increment of heat source temperature and flow rate, and that of four nanorefrigerants are higher than that of pure R123. There is no optimum value of heat transfer coefficient when operation condition is changed for the loading carrying capacity increasing with the increasing intensity of operation condition. Meanwhile, suspending nanoparticles and increasing heat source temperature can change the variation tendency of heat transfer coefficient along flowing direction except pure R123 and 0.18 vol% nanorefrigerant. In addition, 0.13 vol% as a whole is the optimum volume concentration for both log-mean temperature difference and differential pressure.Graphical abstractThis paper presents an experimental investigation of heat transfer performances including heat transfer coefficient along flowing direction, log-mean temperature difference and differential pressure of pure R123 and four volume concentrations 20 nm Al2O3-R123 nanorefrigerants with various volume concentrations 0.03%, 0.13%, 0.18%, 0.23% flowing inside a double-tube counter flow heat exchanger of an organic Rankine cycle system under the conditions of various heat source temperatures and flow rates. A comparison has been made between pure R123 and four kinds of nanorefrigerants to find out the influences of different nanoparticles volume concentrations on local heat transfer coefficient and variation tendency (straight lines) along flowing direction in evaporator. By using polynomial fitting where polynomial order is 3, the polynomial fitting curves (dash lines) and the optimum of volume concentration has been acquired, which indicates the loading carrying capacity in each operation condition.Graphical abstract for this article
       
  • Modelling the water transport behavior in organic-rich nanoporous shale
           with generalized lattice Boltzmann method
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Tao Zhang, Xiangfang Li, Xiangzeng Wang, Jing Li, Wei Li, Wen Zhao, Tianfu YaoAbstractThe hydraulic fracturing fluid could easily infiltrate the ultra-tight shale matrix due to the large slip of the liquid flow, showing higher-than-expected fluid-loss in varieties of shale gas development cases. One possible reason is that the water transport behaviors through the pores with nanoscale significantly deviate from that occurring at larger scales. The classic Darcy law, being widely and successfully used in conventional porous media becomes insufficient for the nanoporous shale. In this study, a generalized lattice Boltzmann method with liquid slip effect incorporated is established to understand the transport behavior of hydraulic fracturing fluid in nanopores dominated shale matrix and to demonstrate a new insight into the transport behaviors. The results show that the flow capability of fracturing fluid in the shale matrix with strong hydrophobic organic nanopores is significantly improved due to the huge wall-fluid interaction. And this would considerably change the flow field (magnitudes and preferred pathway) with and without the micro-fractures, contributing a lot to the huge hydraulic fracturing fluid loss reported from the practical fields. The huge fluid-loss emphasizes the importance for liquid slip effect in organic nanopores of shale matrix. Especially, in the organic-rich shale gas reservoir, the fracturing fluid can be infiltrated into the ultra-tight shale formation easier than commonly expected during the hydraulic fracturing operation.
       
  • WSGG correlations based on HITEMP2010 for gas mixtures of H2O and CO2 in
           high total pressure conditions
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Felipe R. Coelho, Francis H.R. FrançaAbstractThis study presents weighted-sum-of-gray-gases (WSGG) model coefficients for mixtures of H2O and CO2 with fixed mole ratio of 2/1 for high total pressure conditions. The mole ratio represents typical products of stoichiometric combustion of methane in air, which has received significant attention for high pressure applications. The coefficients are based on HITEMP2010 database, and are valid for path-lengths ranging from 0.01 to 30 m, temperatures varying from 400 to 2500 K, and total pressures of 1.0, 2.0, 5.0, 10, 20, and 40 atm. As a first validation of the WSGG model, a comparison with benchmark line-by-line (LBL) total emittance is presented, showing accurate results. Total emittance is shown to have significant pressure dependence, which emphasizes the importance of generating WSGG coefficients fitted to high pressure emittance values. To better assess the model accuracy, calculations for radiative heat flux and volumetric source are performed for two one-dimensional test cases, considering nonisothermal, homogeneous and non-homogeneous conditions. Results show acceptable deviations from the LBL solution for the homogeneous case, with even lower deviations for the non-homogeneous case, as long as the ratio between the species is fixed at 2/1. The effect of pressure is also significant on both radiative heat flux and volumetric source, while its behavior shows that interpolation is a good alternative to obtain WSGG solutions for intermediate pressures.
       
  • Sweat effects on the thermal analysis of epidermal electronic devices
           integrated with human skin
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Yun Cui, Yuhang Li, Yufeng XingAbstractEpidermal electronic devices (EEDs) are widely used in many applications especially directly integrated with human skin tissue to monitor the vital signs of human body. The thermal management of EEDs is very critical because the excessive temperature increase may cause discomfort or damage to human skin. Sweating can also significantly change the thermal environment of EED/skin system due to its function on the thermal transport process. A three-dimensional heat transfer analytical model is established to predict the thermal characteristics of EED/skin system considering the bio-heat transfer and effects of sensible sweat. In this model, the heat conductions in EEDs and in human skin are taken into account with Fourier heat transfer equation and Pennes bio-heat transfer equation, respectively, including the transport process of sweating. The results are validated by finite element analysis (FEA) and parameters studies such as velocity of sweat, thermal conductivity and thickness of substrate have been investigated. The results can help guide the thermal management of EED/skin system considering effects of sensible sweat.
       
  • Study on in-situ measurement method of THF hydrate thermal conductivity
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Shicai Sun, Xiao Jin, Changling Liu, Qingguo Meng, Yong ZhangAbstractThe HotDisk thermal constants analyzer based on the transient plane source (TPS) technique can be used to measure the hydrate thermal conductivity. In order to improve the measurement accuracy, the HotDisk setting parameters, the sample preparation and measurement method are investigated in this paper. Firstly, the evaluation criteria are proposed to determine the optimal setting parameters, mainly the output power and measurement time. Four kinds of method of the sample preparation and thermal conductivity measurement in situ are proposed and discussed. The used samples include pure Tetrahydrofuran (THF) hydrate, ice and THF hydrate or ice bearing silica sand. The results show that the optimal parameters of the output power and measurement time depend on the sample. A high purity of sample can be obtained using the temperature oscillation-aging method and the accuracy of measurement can be further improved using the “increasing temperature-decreasing temperature” method.
       
  • Experimental study on the constituent separation performance of binary
           zeotropic mixtures in horizontal branch T-junctions
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Wen Su, Yunho Hwang, Nan Zheng, Shuai Deng, Li ZhaoIn this paper, the constituent separation performance of binary zeotropic mixtures, R134a/R600a, in horizontal branch T-junctions was experimentally investigated. The effects of flow conditions, mixture compositions and T-junction geometries on the constituent separation performance were studied. During the experiments, the inlet mass flux and quality were varied from 200 to 300 kg·m−2·s−1 and from 0.1 to 0.9, respectively. Meanwhile, the mass flux of the branch was regulated by keeping the branch-inlet mass flow ratios of 0.3 and 0.5. Furthermore, constituent distributions were compared for three different inlet R134a mass fractions, namely 0.3030, 0.5202 and 0.7053. The required mass fractions of R134a at the inlet and outlet of T-junctions were calculated based on the measured liquid density. As for the T-junction geometry, the diameter ratio of the branch tube to the inlet tube was set to be 0.75 and 1.0, and three branch angles, namely 45°, 90°, 135°, were considered. In order to represent the degree of actual separation to the complete separation, constituent separation efficiency is defined as the difference of the fractions of constituents taken off in the branch. Based on the generated experimental data, it’s found that there generally exists an inflection point of separation around the vapor quality 0.2. Before the inflection point, the efficiency generally increases with the increase of inlet vapor quality. After that, the separation efficiency gradually decreases from the positive to the negative. It means that more R600a is extracted into the branch, due to the lower vapor density and vapor dynamic viscosity. Furthermore, for the three mixture compositions, R134a/R600a with an R134a fraction of 0.3030 has the best constituent separation performance. The largest variation range of outlet fraction is from 0.2559 to 0.3443 under the mass flow ratio of 0.3 and mass flux of 200 kg·m−2·s−1. However, the highest separation efficiency 9.49% is obtained under the mass flow ratio of 0.5. As for the effect of T-junction geometry, when the inlet quality is less than 0.4, increasing the diameter ratio can enhance the constituent separation. Compared with the angles 45° and 135°, the largest separation capacity is obtained by the angle 90°.Graphical abstractGraphical abstract for this article
       
  • Natural convection of a nanofluid between two eccentric cylinders
           saturated by porous material: Buongiorno’s two phase model
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): Mohsen Izadi, Sara Sinaei, S.A.M. Mehryan, Hakan F. Oztop, Nidal Abu-HamdehAbstractThis paper concerns with a numerical study on heat transfer by natural convection of different nanofluids inside a porous medium between two horizontal eccentric cylinders. The Buongiorno’s model was utilized to track the nanoparticles concentration. Heat transfer by natural convection of water-copper, water-diamond and water–silicon dioxide nanofluids inside a porous medium between two cylinders was studied. A set of characteristic equations were solved using finite element method. Range of parameters which are studied are Ra = 103-106, Da = 10−6-10−3, ε = 0.1–0.9 and volume fractions of 0.0–0.1, Nr = Nt = Nb = 0.1–0.5, and Le = 1–10. The porous medium was analyzed by Darcy-Brinkman model. The results showed that thermophoresis parameter and Brownian parameter have no significant effect on isothermal lines and the streamlines. The probability of collision of nanoparticles decreases with increasing the Lewis number, which consequently decreases the average Nusselt number. The maximum and minimum enhancement in natural convection was detected in water-diamond and water–silicon dioxide respectively.
       
  • Thermal analysis of cellulose nanocrystal-ethylene glycol nanofluid
           coolant
    • Abstract: Publication date: December 2018Source: International Journal of Heat and Mass Transfer, Volume 127, Part BAuthor(s): L. Samylingam, K. Anamalai, K. Kadirgama, M. Samykano, D. Ramasamy, M.M. Noor, G. Najafi, M.M. Rahman, Hong Wei Xian, Nor Azwadi Che SidikAbstractIn this paper, cellulose nanocrystal (CNC) – ethylene glycol (EG) + Water (W) based nanofluid was developed and assessed for their thermophysical properties and the usefulness towards machining performances. The nanofluid was prepared by adopting two-step preparation method and at volume concentration of 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3% and 1.5%. The nanofluid with 1.3% and 1.5% concentration showed to have superior the conductivity properties, around 0.559 W/m·K at 70 °C. However, the 0.5% concentration has the highest stability with 0.52 W/m·K at 70 °C. The 0.5% nanofluid concentration was then selected for the machining performance evaluation. The machining performance was evaluated by using a lathe machining operation to determine the heat transfer and tool life properties. The cutting variables such as cutting speed, depth of cut and feed rate are varied to understand the effect of developed nanofluid on the machining bahaviour. Findings revealed that the tool failure on machining using MWF is flank wear, chipping and abrasion and fractured at the maximum cutting distance of 500 mm. However, machining using CNC-EG+W nanofluid revealed the tool failure to be flank wear, adhesion and build- up-edge (BUE) and fractured at the maximum cutting distance of 772 mm.
       
 
 
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