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International Journal of Heat and Mass Transfer
Journal Prestige (SJR): 1.498
Citation Impact (citeScore): 4
Number of Followers: 336  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0017-9310 - ISSN (Online) 0017-9310
Published by Elsevier Homepage  [3181 journals]
  • Non-linear analysis of nitrogen pressure drop instability in
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Yiwu Kuang, Wen Wang, Jianyin Miao, Hongxing Zhang, Xin'gang Yu Pressure drop instability of nitrogen flow boiling in micro/mini-channels challenges the application of nitrogen in the cooling & heat dissipation areas by causing unstable flows, oscillations of flow rate, temperature and pressure. In the present study, a non-linear analysis of nitrogen flow boiling instability is conducted. By introducing the structure number, a novel stability criterion consisting of 4 dimensionless numbers are proposed. Based on the criterion a stabilization map is obtained and validated with experimental data from different researchers. Influences of acceleration pressure drop, saturation pressure, channel length, diameter and length-diameter ratio on the stabilization map are investigated. It is found that acceleration pressure drop plays a significant role in the nitrogen flow boiling instability and has opposite effects to the frictional pressure drop. Increasing of saturation pressure generally stabilizes the nitrogen boiling flow by compressing the unstable region on the stabilization map. Besides, these is a maximum allowable subcooling number which ensures the flow boiling system to be inherently stabile if it is not exceeded. And it increases with the growth of saturation pressure. Furthermore, channels with the same length-diameter ratio have very similar stabilization map. Length-diameter ratio can be a significant parameter for further similarity analysis of nitrogen flow boiling instability.
  • Study on Ledinegg instability of two-phase boiling flow with bifurcation
           analysis and experimental verification
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Feng Liu, Zhuqiang Yang, Bo Zhang, Tianhui Li Some new phenomena of Ledinegg instability are observed by portraying a complete flow excursion process via bifurcation analysis and experimental verification. A mathematical model consisting of two first-order nonlinear ordinary differential equations, is constructed via the lumped parameter method and verified through linear stability analysis. The results of bifurcation analysis show that Ledinegg instability corresponds to saddle-node bifurcation, which is consistent with previous literatures. The minimum point of the internal curve is not necessarily the onset of flow instability (OFI). It is equivalent, for the saddle-node bifurcation point, OFI and the tangent point between two characteristic curves, to indicate flow excursion. The flow excursion process is unidirectional and irreversible at OFI, which decides that hysteresis phenomenon can be triggered by Ledinegg instability within the unstable bifurcation interval. Conversely, hysteresis phenomenon determines there exist two types of flow excursion and OFIs, namely, Type I and Type II which respectively correspond to decrease and increase in mass flux. Hysteresis phenomenon indicates not only that the system cannot autonomously returns to the original operating state once flow excursion occurs, but also that the sufficient and necessary condition of flow excursion is that current equilibrium state crosses over the corresponding OFI in the same equilibrium branch. To avoid the occurrence of Ledinegg instability, a versatile quantitative criterion is developed by considering two characteristic forces simultaneously. Finally, experimental results verify the correctness of bifurcation analysis.
  • On the temperature field in the creep feed grinding of turbine blade root:
           Simulation and experiments
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Qing Miao, Hao Nan Li, Weng Feng Ding Although there have been many theoretical, numerical and experimental studies focusing on grinding temperature, very few of them investigated the temperature domain when performing profile grinding of free-form surfaces, where excessive heat can be considered as the key issue due to the long and complex contact zone. In this study, the finite element (FE) based thermal model of the Creep Feed Grinding (CFG) process of Inconel 718 turbine blade root was established in terms of energy partition, material properties, geometry, and thermal boundary. The validation experiments aided with the imbedded thermocouples showed the reasonable match with the experimental results where the average difference was of about 20% proved the simulation feasibility and accuracy. The effects of the blade root profiling and root geometry on the grinding temperature were discussed based on the validated FE model. Considering the research gaps mentioned above, this work is not only expected to be meaningful to deepen the understandings of the temperature field distribution in the CFG of turbine blade root, but also helpful to provide industry guidance to optimize the process physics in precision machining of high-valued parts with complex profiles.
  • Natural convection of plate finned tube heat exchangers with two
           horizontal tubes in a chimney: Experimental and numerical study
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Han-Taw Chen, Wei-Xuan Ma, Pei-Yu Lin This study uses a hybrid method of computational fluid dynamics (CFD) and inverse heat conduction analysis (IHCA) combined with experimental temperatures to investigate the natural convection of plate finned tube heat exchangers with two horizontal tubes located in a chimney. The influence of the position of the two heated tubes on the results obtained is considered. IHCA combined with experimental temperatures is used to estimate h¯ and h¯b. Subsequently, the CFD commercial software combined with the obtained inverse results and experimental temperatures is employed to get the present results. The results reveal that the zero-equation turbulence model can be applied to determine more accurate results than the other two flow models. Therefore, the appropriate flow model for this study is the zero-equation turbulence model. The fringe pattern for each heated tube is mainly aligned in the vertical direction and the two plumes are slightly inclined toward the inward direction. The obtained velocity pattern and air temperature contour are consistent with existing interferometric images or isotherms. The proposed correlation between Ra and Nu agrees with the obtained inverse and CFD results.
  • Falling liquid film periodical fluctuation over a superhydrophilic
           horizontal tube at low spray density
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Yi Zheng, Guoxin Chen, Xiangdi Zhao, Wanfu Sun, Xuehu Ma Falling film on horizontal tube banks is widely used in heat transfer exchangers and absorbers due to its high heat and mass transfer performance. The superhydrophilic surface can effectively ameliorate the wettability of the tube wall and maintain thin film even at a very low spray density. Both of them play the dominating role in heat and mass transfer process. In this paper, a thermal tracing method was employed to investigate the liquid spreading feature and film fluctuation characteristics over a horizontal superhydrophilic tube. The results showed that the liquid film spreading width for the superhydrophilic tube was two times higher than that of the plain surface. Interestingly, as the liquid film extended continuously along the tube surface, the spreading width exhibited little relevance to the spray density under the current experimental condition for the superhydrophilic tube. Furthermore, in the case of droplet mode, the increment of flow rate leaded to an increase in the frequency of the impacting droplet instead of the droplet volume. Finally, the periodic behavior of liquid film fluctuation in droplet mode was observed as well, which demonstrated higher fluctuation intensity than that of other flow modes. The superhydrophilic-aided drop mode is of value in exploring the efficient, precise, and feasible technique for falling liquid film on a horizontal tube especially for ultralow spray density.
  • Effect of wall stiffness, mass and potential interaction strength on heat
           transfer characteristics of nanoscale-confined gas
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Reza Rabani, Ghassem Heidarinejad, Jens Harting, Ebrahim Shirani The interactive thermal wall model is applied in three-dimensional molecular dynamics simulations to investigate the combined effect of the wall force field, the wall stiffness, the wall atom mass and the wall/gas interaction potential strength on the heat transfer characteristics of static rarefied argon gas within a nanochannel. By increasing the wall stiffness, a reduction in the heat flux through the gas medium occurs which leads to a higher temperature jump. As the wall atom mass is increased up to twice the argon atom mass, the heat flux is enhanced notably and a minimum temperature jump can be found at this point. Further increase in the wall atom mass results in reducing the heat flux and consequently increasing the temperature jump. The increment of the wall/gas interaction potential strength up to four times the one of gas/gas interactions is shown to enhance the heat flux and to reduce the temperature jump until it eventually vanishes. Furthermore, it is found that under such conditions, the density profile experiences a second peak. A further increase of this parameter is found to have a negligible effect on the heat flux through the gas medium and it only increases the second peak in the density profile.
  • Nucleate pool boiling heat transfer on etched and laser structured silicon
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Anže Sitar, Matic Može, Michele Crivellari, Jörg Schille, Iztok Golobič Pool boiling experiments were performed using saturated double-distilled and degassed water on 10 × 10 mm silicon samples, which were (i) untreated; (ii) laser structured; or (iii) modified with etched artificial nucleation cavities. The etched silicon surfaces were fabricated with differently sized micro nucleation cavities (5–30 µm) and pitches (0.125–2 mm) to allow a comparative analysis of the fabricated surfaces. The heat transfer coefficient (HTC) comparative analysis conducted at the heat flux of 200 kW/m2 exhibits the highest enhancement of 244% during nucleate boiling on the silicon sample with etched nucleation cavities with a 30 µm diameter and a 0.125 mm pitch. The experimental results consistently show that HTC increases with decreasing the pitch and increasing the size of the nucleation cavities in the range of the experimental conditions. The superheat required for the onset of nucleate boiling and the critical heat flux were not substantially affected with the structured surfaces. However, the boiling phenomena propagates more promptly to the entire available silicon surface, when the sample is laser treated or etched compared to the reference bare silicon sample.
  • Effect of the wall temperature on Mach stem transformation in
           pseudo-steady shock wave reflections
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Kexin Wu, Senthil Kumar Raman, Vignesh Ram Petha Sethuraman, Guang Zhang, Heuy Dong Kim Pseudo-steady shock wave reflections on a compression ramp are recognized as a significant phenomenon in the shock dynamics field. Several investigations have been performed on this phenomenon by shock tube experiments, combined with numerical and theoretical analyses. In addition to the availability of numerous reliable and accurate data on shock reflection patterns in the form of regular reflection, double-Mach reflection, transitional-Mach reflection, and single-Mach reflection, several transitional criteria such as detachment criterion and mechanical-equilibrium criterion are also established. However, none of the research focuses on the influence of the wall temperature on Mach stem transformation in pseudo-steady shock wave reflections. In order to articulate the role played by the wall temperature, a two-dimensional numerical simulation is performed by resolving the unsteady Reynolds-averaged Navier-Stokes equations to investigate the transformation of the Mach stem. Shear-stress transport k-ω turbulence model and third-order Monotonic Upwind Scheme for Conservation Laws scheme are explored to accurately capture various shock structures. Numerical results are initially validated with experimental data in the open literature and it is evident that there is an excellent match between the present simulation and the actual structure. Subsequently, the grid resolution and time step independence analyses are considered to better resolve the shock reflection configuration. Large-scale negative and positive heat fluxes are imposed on the ramp wall, which can simulate the cooling and heating ramps respectively. A new Mach stem transformation that illustrates significant differences in physical structure evolutions caused by the variation of the wall temperature is numerically captured for the first time. The mechanism of wall temperature effects on the transformation of the Mach stem is clearly expounded with the purpose of profound understanding for pseudo-steady shock wave reflections.
  • On reactive thin liquid films falling down a vertical cylinder
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Youchuang Chao, Yongjie Lu, Hao Yuan Chemical reactions in thin liquid films falling down vertical cylinders are widely present in various industrial settings, such as in combustion chambers of internal combustion engines. However, the effect of chemical reactions, especially the non-isothermal reactions, on the dynamics of thin films remains poorly understood. Therefore, in this paper, we systematically study the dynamics of a thin liquid film flowing down vertical cylinders in the presence of an exothermic or endothermic chemical reaction. A reduced model based on the assumption that the film thickness is much smaller than the cylinder radius is firstly derived. We then examine the effect of chemical reactions on the linear stability of the evolution equation as well as its nonlinear behaviors, including the profile and propagation speed of steady traveling waves. We find that the size and propagation speed of sliding beads on the cylinder are suppressed for an exothermic chemical reaction and promoted for an endothermic chemical reaction, respectively. In the end, we perform direct numerical simulations of the full nonlinear evolution equation, which are consistent with the predications from linear stability analysis and nonlinear traveling wave solutions. Our results provide new insight into the influence of chemical reactions on the dynamics of thin films falling down the cylindrical substrate.
  • Experimental investigation of the heat transfer performance of
           capillary-assisted horizontal evaporator tubes with sintered porous
           hydrophilic copper-carbon nanotube-titanium dioxide (Cu-CNT-TiO2)
           composite coatings for adsorption chiller
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Edward Joshua T. Pialago, Jinho Yoo, Xiru Zheng, Byung Ryeon Kim, Sung Joo Hong, Oh Kyung Kwon, Chan Woo Park A partially flooded evaporator is often used in adsorption chiller. This study explores the use of a ternary copper-carbon nanotube-titanium dioxide (Cu-CNT-TiO2) composite coating on copper tubes with structured external surfaces for the enhancement of capillary-assisted water evaporation in semi-flooded evaporator. The composite coating, made from ball-milled composite powder, was deposited on the tube by electrostatic spraying and consolidated by sintering in an electric furnace. The coating samples were characterized by pore size, surface porosity, pore density and optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The wettability of the coated-surfaces with a droplet of refrigerant, i.e., water, was observed at atmospheric conditions by measuring the contact angle between water droplets and the surface. These characterizations showed that the Cu-CNT-TiO2 coating had a porous surface structure and was more wettable than the pure copper coating. To investigate the influence of the applied coating and water level fraction on heat transfer, experiments for evaporation heat transfer were performed at a saturated water vapor pressure of 7.5 torr (~1 kPa) and a warm water inlet temperature of 12 °C with an evaporator with four serially connected tubes. Enhanced evaporation heat transfer was achieved when the heating tubes were partially immersed in water with level ratios of approximately 0.1 to 0.3 (i.e., 10 to 30% of the tube diameter). Furthermore, use of the Cu-CNT-TiO2 coating improved the evaporation heat transfer, especially when applied to the finned tubes; a maximum enhancement ratio of 3.15 was obtained, comparing the Cu-CNT-TiO2-coated finned tubes with the bare finned tubes.
  • A study on the effect of oxidation on critical heat flux in flow boiling
           with downward-faced carbon steel
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Kai Wang, Nejdet Erkan, Koji Okamoto To execute in-vessel retention external reactor vessel cooling (IVR-EVRC) successfully, critical heat flux (CHF) plays a key role in securing the thermal and structural integrity of the reactor pressure vessel (RPV). In real-world applications, the RPV outer surface is exposed and oxidized. In this study, we performed a downward-face flow boiling CHF experiment using a carbon steel plate with several boiling cycles under water. Because the direction of gravity was inverse with the normal of the wall, it was difficult to remove bubbles, and in the local area, some local burning could repeat several times. After polishing the surface with sandpaper, the heat was supplied to the surface by cartridge heaters in a step-by-step manner until CHF was reached, after which the surface was cooled down. Using the same surface, without any further surface treatment, this heating cycle was repeated five times. The CHF value increased with the number of cycles. When the experiment was repeated for different mass fluxes, the CHF value also increased with the number of cycles. We suggest that this increasing tendency in CHF is associated with the increasing level of surface oxidation. After every repetition of the heating cycle, surface oxidation level increased, fewer bubbles were observed on the surface, resulting in higher CHF values. After the experiment, surface roughness increased and contact angle decreased. The liquid-vapor mixture area decreased with increasing heat flux in one experiment, whereas it decreased with boiling time, under the same heat flux, which delayed CHF. The gradual oxidation process of carbon steel could be beneficial for real-world applications of IVR-ERVC.
  • Application of an improved parameter estimation approach to characterize
           enhanced heat exchangers
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Pamela Vocale, Fabio Bozzoli, Andrea Mocerino, Kristina Navickaitė, Sara Rainieri The main goals of this paper are twofold: to provide an improved parameter estimation procedure that enables the accurate evaluation of heat transfer correlations for the Nusselt number and to present a new procedure for identifying the presence of transition in the flow regime.In the first goal, it needs to be pointed out that although this kind of approach is based on temperature measurements, in the literature, the classical parameter estimation approach uses the overall heat transfer coefficient. To reduce uncertainty in the evaluation of internal and external heat transfer coefficients, in the improved procedure, the measured temperature data were directly used without any intermediate elaboration.The validation of the new procedure, carried out by means of synthetic data, highlighted that both the relative error on each estimated parameter and the amplitude of the confidence intervals were reduced by minimizing the objective function expressed in terms of outlet temperature of the tube side of the heat exchanger.With regard to the transition regime, the numerical outcomes revealed that both in the laminar and turbulent regimes, the amplitude of the confidence intervals of the estimated parameters was very small; in the transition regime, the amplitude became wide. Therefore, this parameter served as a useful indicator to identify the presence of transition in the flow regime. This finding enabled a new indirect methodology, called the transition alert procedure, to be developed for identifying the Reynolds number value at which transition of the flow regime occurred. This method is an iterative subsampling of the dataset based on the observation of the amplitude of the confidence intervals.To assess the robustness of the methodologies proposed here, the improved parameter estimation procedure and the transition alert procedure were applied to the obtained experimental data by analyzing a counter-flow heat exchanger with double corrugated tubes. In this kind of tube, the condition when the transition from the laminar to the turbulent flow regime occurs is not known a priori.
  • Thermohydraulic analysis of a new fin pattern derived from topology
           optimized heat sink structures
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Shi Zeng, Qiuzhuang Sun, Poh Seng Lee This paper presents a new fin pattern for liquid-cooled microchannel heat sinks. It is derived from topology optimized heat sink structures reported in our previous paper. The new fin pattern is composed of two types of fins, oblique fin and trapezoidal fin, and they are arranged in a semi-wavy manner. Numerical simulation is implemented to examine its heat transfer and fluid flow characteristics in detail. A flow phenomenon that is similar to Dean’s vortices is observed and results in enhanced flow mixing. The non-continuous fin pattern also avoids growth of thick boundary layers as they are initiated at the leading edges of each fin. Furthermore, size optimization based on the response surface method is performed to balance the heat transfer enhancement and pressure drop penalty. The new fin pattern is then compared with five other commonly used fin designs and shows the best performance in the studied flow range.
  • Free-surface flow of confined volatile simple fluids driven by a
           horizontal temperature gradient: From a comprehensive numerical model to a
           simplified analytical description
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Tongran Qin, Roman O. Grigoriev We study the flow in a confined layer of volatile simple liquid subjected to a horizontal temperature gradient. The somewhat unusual feature of this problem is that the gas layer, which contains a mixture of vapor and air, plays a very important role. Due to phase change occurring at the free surface, the mean flow in the liquid layer and its stability are controlled almost entirely by the mass and heat transport in the gas phase. To explain why this is the case, we use numericae simulations based on a comprehensive two-sided transport model to motivate a simplified analytical description of transport in the gas phase for high-aspect-ratio geometries. This simplified description allows us to compute the interfacial temperature and hence the thermocapillary stresses at the free surface which control the flow in the central region of the cavity and to predict the net heat and mass flux in the direction of the applied gradient. The analytical solutions are found to agree quite well with the results of our numerical simulations as well as the results of relevant previous studies.
  • Passive anti-frosting cables
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Lance H. De Koninck, S. Farzad Ahmadi, Jonathan B. Boreyko Buildup of ice and frost on overhead transmission lines compromises their integrity and also poses a danger to surrounding infrastructure and people. We present a passive anti-frosting cable design that keeps the majority of the surface free of condensation and frost, effectively preventing a continuous layer of ice from forming. The design consists of an array of rings, each containing a wicking micro-groove, that are evenly spaced across the aluminum cable. Water preferentially wets the grooves and freezes into ice rings at cold temperatures. As ice exhibits a depressed vapor pressure relative to liquid water, these ice rings act as overlapping humidity sinks. Two supersaturations were tested, an extreme supersaturation of 3 to best measure frost accumulation through video analysis and a supersaturation of 1.5 more reminiscent of real-life outdoor conditions. Regions between rings remained dry indefinitely beneath a critical ring spacing whose value depended primarily upon the supersaturation and secondarily upon the ring diameter. In contrast, continuous sheets of frost grew on aluminum cables that were smooth and initially dry, even when treated with a superhydrophobic coating.
  • Cross flow and heat transfer of hollow-fiber tube banks with complex
           distribution patterns and various baffle designs
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Kui He, Li-Zhi Zhang The pressure drop and heat transfer of hollow-fiber tube banks with various packing patterns and baffle designs are studied by combining pattern recognition technology and computational fluid dynamics. The fluid passes across the fiber bank. The inlet flow Reynolds number ranges from 20 to 180. The pressure drop and heat transfer coefficients of the contactors are highly correlated to the topological characteristics of the fringe of the fiber bank. A single parameter ψ, which summarizes this information, is calculated using pattern recognition technology. The pressure drop and Nusselt number of a contactor exhibit power law relations with ψ. Interestingly, this phenomenon is independent of the baffle design, which affects only the magnitude of the pressure drop and the heat transfer coefficient. Generally, a higher ψ results in contactors with worse performance. For ψ>  0.6, the wall effect is negligible, and all contactors show similar performance regardless of the fiber pattern. The comprehensive performance parameter ∅ is approximately 0.6 for all contactors with various patterns. An ‘‘insert’’ strategy that is used to reduce ψ is demonstrated. The results show how to optimize the structure of contactor for industrial production.Graphical abstractThe correlation of the performance of hollow fiber membrane contactors with topology parameters of them σw = Sw/D, ψ = γ/α, where D = 25 mm. 1 is the artificial fibers on the wall of a contactor.Graphical abstract for this article
  • Molecular dynamics study of rapid boiling of thin liquid water film on
           smooth copper surface under different wettability conditions
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Nini Wu, Liangcai Zeng, Ting Fu, Zhaohui Wang, Chang Lu This work aims to present theory of heat transfer on rapid boiling for pure wettability surfaces and mixed wettability surfaces based on molecular simulation. The simulation results showed that the temperature of water increased obviously and the maximum evaporation rate of water reduced significantly with the increase of hydrophilic for pure wettability surfaces. Furthermore, a microfluidic layer which was formed on all cases except hydrophobic surface (surface 4) was conducive to critical heat flux (CHF) improvement. Meanwhile, the attraction of water molecules upon hydrophobic region was smaller than that on hydrophilic region which was conducive to boiling heat transfer coefficient (HTC) improvement. A mixed wettability surface enhances boiling heat transfer by regulating vapor spreading behaviors over the heating copper surface compared with pure wettability surfaces.
  • Numerical simulation of multiprobe cryoablation synergy using heat source
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): I.A. Burkov, A.V. Pushkarev, A.V. Shakurov, D.I. Tsiganov, A.A. Zherdev During percutaneous multiprobe cryoablation, a group of microthrottle heat exchangers are destroying undesired biological tissues. To improve this treatment, thermophysical prediction software is being developed. However, there are not all cryosurgery parameters and other influencing factors that are correctly considered. Among them are the boundary conditions (that replace cryoprobe during simulation), the thermophysical properties of biological tissues, and the mutual influence between cryoprobes (which causes the effect of the cryonecrosis isotherm volume synergy). In this paper, the heat source boundary based on experimentally obtained temperature distribution along the active part of argon cryosurgery system cryoprobes is proposed. It depends on the temperature of the biological tissue surrounding the cryoprobe surface. Transient heat transfer problem using temperature-dependent thermophysical properties of biological tissues and typical cryosurgery parameters is solved. Based on this, the effect of the cryonecrosis isotherm volume synergy is shown. The results indicated the area of cryosurgery parameters in which synergy cannot be neglected. This information is expected to be useful for understanding the quality of cryoablation planning algorithms.
  • Air-side heat transfer and pressure drop characteristics of microchannel
           evaporators for household refrigerators
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Joel Boeng, Arthur A. Marcon, Christian J.L. Hermes Microchannels are likely to be the next heat transfer technology for household refrigerating applications, especially due to their compact design and high heat transfer rate per unit of volume. In contrast to the conventional tube-fin evaporators, the available heat transfer and pressure drop correlations are not well-stablished yet. This study introduces a new microchannel evaporator design to be used in ‘no-frost’ household refrigerators. The performance of sixteen evaporators prototypes with distinct geometric characteristics were evaluated experimentally in an open-loop wind-tunnel calorimeter facility coming up with data for the overall thermal conductance and the air-side pressure drop data as a function of the air flow rate. Empirical correlations for Colburn j-factor and friction f-factor were devised in terms of the Reynolds number and key compact heat exchanger parameters, being able to predict 90% of the experimental counterparts within ±10% and ±20% error bands, respectively. Furthermore, comparisons against a typical no-frost tube-fin evaporator was carried out with respect to air-side pressure drop and overall thermal conductance, which indicated a promising potentiality of application in household refrigeration appliances.
  • An additively manufactured novel polymer composite heat exchanger for dry
           cooling applications
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): M.A. Arie, D.M. Hymas, F. Singer, A.H. Shooshtari, M. Ohadi The work presented in this paper focuses on the design and thermal characterization of a novel polymer composite heat exchanger (HX) produced by an innovative additive manufacturing process. The heat exchanger represents a gas to liquid configuration in which the gas side removes heat from the liquid side in a cross-flow arrangement. The novel HX utilizes a cross media approach in which, unlike the conventional HXs, the hot and cold sides are directly connected to each other through high conductivity metal fiber fins on the gas side protruding through the walls of the liquid side, thus eliminating the wall resistance separating the hot and cold sides. The HX demonstrates superior thermal performance at reduced pressure drops while also benefiting from the lighter weight and the lower cost that the polymer structure introduces. A 350-W water-to-air heat exchanger was fabricated using a fused filament fabrication (FFF) technique with a novel/patent pending printer head which was developed to produce the metal fiber composite structure of the heat exchanger. The results of the heat exchanger characterization tests show that it yields up to 220% and 125% improvement in heat flow rate over mass (Q/m) and heat flow rate over volume (Q/V), respectively, when compared to comparable state-of-the-art plate fins HX configurations. This study in particular demonstrates the impact of additive manufacturing in realizing potentially transformative heat exchanger technologies that may otherwise be very difficult to achieve with conventional fabrication methods.
  • Thermal transport across graphene-mediated multilayer tungsten
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Wenlong Bao, Zhaoliang Wang, Jie Zhu The thermal conductivity of monolayer graphene/β-phase tungsten (β-W) periodic stack nanostructure and the interfacial thermal resistance induced by graphene have been measured by a modified two-color femtosecond laser pump-probe technique. The thickness of β-W films is 15, 30, 40 nm respectively, and the total thickness of periodic stack nanostructures is about 120 nm ignoring the thickness of graphene. The cross-plane thermal conductivity (k) of β-W film is determined as 7.58 W/m K which is two orders of magnitude smaller than that of α-phase bulk tungsten. The small value is attributed to the vacancies in β-W and the small grain size of β-W, which can suppress the mean free path of hot carriers. The cross-plane thermal conductivity of periodic stack nanostructure is smaller than the value of pure W film and gradually decreases with the increasing number of graphene layers. The interfacial thermal resistance between the monolayer graphene and the tungsten films ranges from 4 × 10−9 to 8.15 × 10−9 m2 K/W. The results predicted by the diffuse mismatch model are smaller than the experimental results, indicating that the phonon inelastic scattering plays an important role in the heat transport of W/graphene periodic stack nanostructure.
  • Thermophoresis of nanoparticles in liquids
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Saran Ramachandran, C.B. Sobhan, G.P. Peterson Thermophoresis is the movement of particles in a fluid subjected to a steady temperature gradient, where the fluid molecules at the hotter region possessing higher kinetic energy drive the particles towards the colder region. This paper presents a molecular dynamics simulation to obtain the effects of the particle shape, size and orientation on thermophoresis in nanofluids. Two allotropes of carbon, namely Carbon Nanotubes (CNT) and fullerene, and copper nanoparticles have been studied, with liquid argon and water as the base fluids. It was found that the thermophoretic force in fullerene particles of comparable size is more than that in CNT. It was also seen that the particle orientation and size have an effect on the thermophoretic force, and that the force decreases with an increase in the particle size. The effect of the base fluids, namely liquid argon and water, on the thermophoretic force was also studied, and a comparison was performed using the thermophoretic coefficient. The simulation results show that the thermophoretic force is proportional to the kinematic viscosity of the fluid and the imposed temperature gradient, and the increase is found to be linear. The results also indicate that the thermophoretic force depends on the particle orientation, and the analysis provides a starting point for further studies to explain the functional dependence of the particle orientation on the thermophoretic force.
  • Ablation of polyimide thin-film on carrier glass using 355 nm and
           37 ns laser pulses
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Yoonsuk Kim, Youngsu Noh, Seungho Park, Byung-Kuk Kim, Hyoung June Kim Ablation of the polyimide (PI) thin-film deposited on glass substrate was investigated theoretically and experimentally to find out the important characteristics during the laser-lift off (LLO) process for the fabrication of flexible electronics. Instead of using conventional ablation induced by the front irradiation on the specimen, the LLO process employs the backside irradiation on the specimen transferred through the glass substrate, assuming that the ablation occurs volumetrically in the narrow region inside the PI film near the PI and glass interface. Experimentally the PI film on glass was exposed to a pulse laser beam emitted from UV laser of 355 nm in wavelength and 37 ns in duration. Depths and morphologies of the ablation spots were observed by the surface profiler and the FE-SEM. Theoretically the ablation process was estimated by the photothermal mechanism, using the one-dimensional heat conduction equation with volumetric absorption of the laser beam. It was shown that the experimental ablation could be described through the theoretical analysis based on the surface and the bulk photothermal models. While the former assumed that the ablation occurred only on the ablation front surface, the latter assumed the ablation was accompanied by the thermal and volumetric bond breakage. In general, the theoretical calculations agreed well with the experimental observations. In particular, the experimental observations of the ablation for the backside irradiation case that was the core phenomenon in the LLO process was explained appropriately by the features predicted using the bulk model.
  • Efficient and robust prediction of internal temperature distribution and
           boundary heat flux in participating media by using the Kalman smoothing
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Shuang Wen, Hong Qi, Zhi-Tian Niu, Lin-Yang Wei, Ya-Tao Ren The Kalman smoothing (KS) technique, which is consisted of the Kalman filtering and Rauch-Tung-Striebel smoothing technique, is introduced to resolve the inverse radiation-conduction heat transfer problem by using the future temperature measurement information. For the forward problem, the discrete ordinate method is employed to solve the radiative transfer equation and the energy equation is resolved by using the finite volume method. The boundary time-dependent heat flux and internal temperature filed in participating media are retrieved in near real time from measurement temperature on the right surface. Different forms of time-dependent heat flux are imposed on the left surface to examine the performance of the proposed algorithm. All the reconstruction results indicate that the KS technique is effective and robust for resolving the retrieval of the boundary time-dependent heat flux and internal temperature fields in near real time. The effect of different parameters on the accuracy and stability of the reconstruction results, including the future temperature information, sampling interval, measurement noise covariance, initial state error, and initial state error covariance, are analyzed in detail. Compared with the KF technique, the reconstruction accuracy of KS technique can be improved obviously. Meanwhile, the time delay and oscillation of reconstructed heat flux are reduced significantly and the deviation of the retrieval temperature is also decreased greatly.
  • Experiments on flow and heat transfer characteristics of a rectangular
           channel with a built-in adiabatic square cylinder
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Apoorv Vyas, Biswajit Mishra, Atul Srivastava Experimental investigation of unsteady flow past a square cylinder confined in a channel and the associated heat transfer phenomena in laminar flow regime is carried out using purely non-intrusive diagnostic technique. A Mach-Zehnder interferometer has been employed to make the path-averaged measurements of the quantities of interest. Five different Reynolds numbers are considered and the heat transfer rates in the channel with and without the presence of square cylinder have been compared in the wake region of the built-in cylinder. Vortex shedding frequencies are determined using schlieren technique. Both the temperature field and the vortex shedding frequencies have been completely determined using non-intrusive techniques. The whole field experimental results depict significant augmentation in the wall heat transfer rates in the presence of a cylinder when compared with its counterpart (channel without cylinder). Flow instabilities induced by the square cylinder alter the thermal boundary layer profile and hence temperature gradients near the channel walls become steeper and consequently the wall heat transfer is significantly increased.
  • Characteristics of flow behavior and heat transfer in the grooved channel
           for pulsatile flow with a reverse flow
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Junxiu Pan, Yongning Bian, Yang Liu, Fengge Zhang, Yunjie Yang, Hirofumi Arima The present study investigates the flow behavior and heat transfer in the grooved channel for pulsatile flow with a reverse flow by experimental and numerical approaches at different Strouhal numbers (from 0 to 0.125) and different oscillatory fractions (from 0.6 to 1.4). The pulsatile flow patterns are visualized by the aluminum dust method, and the numerical model is validated by experimental results. It is observed that the flow is less stable in the reverse acceleration phase. At the same time, streamlines, temperature and vorticity in the upper and lower grooves are asymmetrical. Besides, this instability leads to a remarkable mix between the groove and the main flow and contributes to the enhancement of heat transfer. In addition, the onset of the unstable state gradually delays and the duration of the unstable state reduces with the increase of Strouhal number during the test range when the net Reynolds number is 375 and the oscillatory fraction is 1.4. Also, it demonstrates that the time-averaged Nusselt number increases with oscillatory fraction which suggests that the imposed reverse flow is capable of improving the heat transfer. It is further revealed that the maximum heat transfer enhancement factor is 2.74 when the oscillatory fraction is 1.4.
  • Numerical and experimental study of the thermal rectification of a
           solid-liquid phase change thermal diode
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Zhaonan Meng, Raza Gulfam, Peng Zhang, Fei Ma Phase change materials (PCMs) are highly effective to enhance the sustainability of thermal energy storage, management and control systems. The quest to find other novel applications of PCMs diverts attention towards phase change thermal diodes. However particularly, solid-liquid phase change thermal diodes (SL-PCTDs) suffer from fairly low thermal rectification ratio, hampering their implementation as thermal management and temperature control units. Herein, a SL-PCTD prototype is reported that is capable to access thermal rectification ratio of 3.0, being the highest in the family of SL-PCTDs. With the help of a theoretical model, the design was optimized in terms of bi-terminal length, providing the guideline to physically fabricate and experimentally execute the SL-PCTD. Paraffin wax and calcium chloride hexahydrate have been employed to assemble phase change bi-terminals. In operation, the heat flux was manipulated within a wide temperature bias of 10–40 °C, in both the forward and reverse directions. Also, theoretical model includes the natural convection and liquid-height-dependent effective thermal conductivity of calcium chloride hexahydrate, helping to meet the prerequisites of a high-performance design.
  • Infrared thermography of sorptive heating of thin porous media –
           Experiments and continuum simulations
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Vignesh Murali, Jos C.H. Zeegers, Anton A. Darhuber We have studied the imbibition of water from a stationary nozzle into thin, moving porous media that are suspended in air, as well as the accompanying evaporation and condensation processes. Due to sorptive heating and the latent heat associated with the phase change processes, the temperature of the porous medium becomes non-uniform. We have measured the temperature distributions using infrared thermography as a function of substrate speed. Moreover, we developed a numerical model coupling Darcy flow and heat transfer in the thin porous medium with gas flow, heat and water vapor transport in the surrounding gas phase. The numerical simulations reproduce the measurements very well and point at an intricate buoyancy-induced gas-phase convection pattern.Graphical abstractGraphical abstract for this article
  • Heat retention analysis with thermal encapsulation of powertrain under
           natural soak environment
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): R. Yuan, N. Dutta, S. Sivasankaran, W. Jansen, K. Ebrahimi This paper investigates high fatality modelling of vehicle heat transfer process during natural soak environment and heat retention benefits with powertrain encapsulations. A coupled computer-aided-engineering (CAE) method utilising 3D computational-fluids-dynamics (CFD) and transient thermal modelling was applied to solve buoyancy-driven convection, thermal radiation and conduction heat transfer of vehicle structure and fluids within. Two vehicle models with different encapsulation layouts were studied. One has engine-mounted-encapsulation (EME) and the other has additional vehicle-mounted-encapsulation (VME). Coupled transient heat transfer simulations were carried out for the two vehicle models to simulate their cool-down behaviours of 9 h static soak. The key fluids temperatures’ cool-down trajectories were obtained and correlated well with vehicle test data. Increased end temperatures were seen for both coolant and oils of the VME model. This provides potential benefits towards CO2 emissions reduction and fuel savings. The air paths and thermal leakages with both encapsulations were visualised. Reduced leakage pathways were found in the VME design in comparison with the EME design. This demonstrated the capability of embedded CAE encapsulation heat retention modelling for evaluating encapsulation designs to reduce fuel consumption and emissions in a timely and robust manner, aiding the development of low-carbon transport technologies.
  • Turbulences of the supersonic gas flow during cold spraying and their
           negative effects: A DNS CFD analysis coupled with experimental observation
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): R.N. Raoelison, L.L Koithara, S. Costil, C. Langlade This paper investigates the phenomenological flow during cold spraying through DNS CFD analysis and experimental observations. The transient DNS computation shows that the gas flow begins to be instable inside the nozzle and generates self-sustained intermittent swirls across the nozzle exit due the shearing behavior of the flow. There is alternate swirling within the separated sheared layers on top and then on bottom of the jet, at sporadic time intervals. The swirls are not strictly periodic in nature, but they recur with an irregular frequency. The temperature field exhibits analogous variation and the thermal turbulence produces a heating confinement within the end zone of the nozzle, at the upper wall mostly. This phenomenon matches with the experimental erosion at the same zone due to a thermomechanical softening of the nozzle. The supersonic jet is self-oscillated along the flow direction and becomes more and more turbulent with a development of vorticity shedding at a certain distance from the nozzle exit. There is a transition from a rather stable jet towards a wake pattern that characterizes the vorticity regime. The thermal turbulence shows a development of turbulent plume which provides a clearer visualization of the straight jet and the abrupt transition into wakes. Experimental observations of particles motion ahead the nozzle exit confirm this turbulent behavior of the gas flow. High-speed shadowgraphy using nanoseconds pulsed laser spray illumination shows two regimes of particles kinematics, that is, a nearly straight jet prior to a progressive stream deviation, and then a full dispersion of the particles. Such dispersion makes possible an oblique collision of the particles on the substrate whose negative effects highlighted in the literature are high porosity within the deposit, difficulty of coating formation, and substantial decrease in deposition efficiency. These findings provide further clarifications about how both gas flow and particles flow behave during cold spraying, and how deviation effects due to turbulences of the supersonic expansion may further alter the deposition capability of LPCS that already suffers from a low DE less than 40%.
  • Self-similarity of surface heat transfer fields on a pre-heated
           rectangular plate in an obliquely impinging sonic jet
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Tianshu Liu, Javier Montefort, Scott Stanfield, Steve Palluconi, Jim Crafton This paper presents an experimental study of the time-dependent surface temperature, heat flux and Nusselt number fields on a pre-heated, rectangular aluminum plate due to an obliquely impinging sonic jet at different total pressures. Surface temperatures are measured by detecting the luminescent emission from temperature sensitive paint. An analytical inverse solution of the one-dimensional time-dependent heat conduction equation is used to determine the heat flux from the temperature measurements. When normalized, the ensemble-averaged heat transfer fields (surface temperature, heat flux and Nusselt number) exhibit self-similarity (time-invariance) for different test conditions and therefore are found to exhibit a somewhat universal nature. A theoretical description of the self-similar behavior is presented for scaling experimental heat transfer data. Furthermore, the skin friction fields extracted from surface temperature and heat flux fields reveal generic topological structures of the flows.
  • Thermal management of a power electronic module employing a novel
           multi-micro nozzle liquid-based cooling system: A numerical study
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Farzad Pourfattah, Majid Sabzpooshani In this study, the cooling capability of a novel design liquid jet impingement multi-micro nozzle cooling system for a high heat flux commercial Si-IGBT power modules has been numerically investigated. The Pressure-based finite-volume techniques method is used. High operating temperature and non-uniformity of the temperature distribution of power modules can lead to thermal reliability problems such as module deformation and performance degradation. So, the development of cooling techniques for thermal management and innovation in the design of the cooling system is indispensable. A prominent feature of the designed cooling system is the uniform distribution of the cooling fluid by the micro-nozzles. The effect of mass flow rate and the ratio of the micro-nozzle at three heat fluxes of 100, 175, and 250 W/cm2 on the cooling performance and pumping power have been investigated. Based on the results, in a constant mass flow rate, by decreasing the ratio of the nozzle from 1.0 to 0.45, the temperature significantly decreases while increasing the pumping power is negligible; less than 1 W. When the nozzle ratio is 0.3, the increase in the pumping power is considerable, and using the nozzle ratio less than 0.4 is not recommended. According to the results, at minimum nozzle ratio (0.3) and maximum flow rate, the pumping power is maximum (23 W) and when heat flux on the IGBT is 250 W/cm2, in nozzle ratio of 0.45, and at the minimum flow rate (0.57 lit/min), the operating temperature is 117 °C, and the pumping power is 0.25 W, which can be considered as an optimum case in the present study.Graphical abstractCooling capability of a novel design impinging liquid jets is evaluated numerically. A prominent feature of the cooling system is the uniform distribution of the cooling fluid by the micro-nozzles. At the minimum flow rate (0.57 lit/min), When nozzle ratio is 0.45 the operating temperature is 117°, and the pumping power is 0.25 Watts.Graphical abstract for this article
  • Study on the size of secondary droplets generated owing to rupture of
           liquid film on corrugated plate wall
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Bo Wang, Bingzheng Ke, Bowen Chen, Ru Li, Ruifeng Tian Corrugated plate dryer is a kind of steam-water separation equipment commonly used in nuclear power plants. Therefore, there are many heat and mass transfer phenomena in the corrugated plate dryer. In this paper, the relative height of liquid film rupture in the corrugated plate under different Reynolds numbers is experimentally studied by PLIF method. The equation for calculating the relative height of liquid film is given. Specific position and shape of the liquid film rupture under the horizontal shear of airflow is theoretically derived. Calculation equation of the size of secondary droplet. Based on PLIF method, the size of the secondary droplet generated after liquid film is broken is measured. Conclusions show that results calculated by the fitted equation of relative height of liquid film rupture are in good agreement with the experimental results. At the small and medium Reynolds number regions (Re 
  • Numerical study on the heat transfer enhancement and pressure drop inside
           deep dimpled tubes
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Mohammad Hassan Cheraghi, Mohammad Ameri, Mohammad Shahabadi Heat transfer enhancement is important from the industry point of view. In this study, a new configuration of enhanced tubes has been investigated numerically. The geometry of this new type of tube was provided by exerting deep dimples on the conventional plain tube. Flow-field and heat transfer characteristics of deep dimpled tubes have been studied, and the effects of the various configuration of dimples comprising three different pitches, diameters, and depths of dimples resulting in twenty-seven configurations have been investigated. Performance Evaluation Criteria (PEC), which is commonly used in heat transfer enhancement subjects, has been studied for all geometries. Local temperature, velocity, streamline, and Nusselt number of the deep dimpled tube have been depicted in comparison to the plain tube to study thermo-fluid characteristics. The investigation for each configuration has been done in three different Reynolds numbers: Re = 500, 1000 and 2000, and k-ɛ turbulent model has been utilized in numerical studies. The higher heat transfer rate of deep dimpled tubes has been seen in higher depth and diameter and lower pitch up to 600%, while this lead to the intense growth of friction factor. It has been observed that PEC of the deep dimpled tubes generally varies from PEC = 1.15–3.3 in different cases. Furthermore, increase in the diameter, pitch and Reynolds number, and decrease in the depth, lead to augmentation of PEC of deep dimpled tubes which escalates up to PEC = 3.3 at Re = 2000 when Diameter = 18 mm, depth = 2 mm, and pitch = 4D.
  • High efficient solar evaporation by airing multifunctional textile
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Guilong Peng, Shichen Deng, Swellam W. Sharshir, Dengke Ma, A.E. Kabeel, Nuo Yang Solar evaporation is important for many applications such as desalination, power generation and industrial drying. Recently, some studies on evaporation reported obtaining high energy efficiency and evaporation rate, which are based on floating evaporation setup (FES) with nanomaterials. Here, a new cheap and simple setup is proposed, named as airing evaporation setup (AES). Compared to FES, there are four advantages of AES: a better thermal design, a higher energy efficiency, a higher material utilization ratio, and multi-function. It shows that the energy efficiency of AES reaches up to 87% under 1 kW/m2 of solar irradiation, which is 14% higher than that of FES. Meanwhile, the total evaporation rate of AES is about 20% higher than that of FES. The theoretical analysis reveals that the main reason for a better performance of AES is the increasing evaporation area. More interestingly, AES could be used for designing portable systems due to its simplicity and flexibility. Furthermore, it is shown that AES and the corresponding wick material can be used in solar desalination, textile quick-drying and warm-keeping.Graphical abstractBy airing wick materials, i.e. airing evaporation setup (AES), the solar evaporation rate is much higher than that of the current nanofluidic evaporation setup (NES) and floating evaporation setup (FES).Graphical abstract for this article
  • Nonlinear thermal conductivity of periodic composites
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Gaole Dai, Jiping Huang Composites have been widely used to realize various functions in thermal metamaterials, thus becoming important to predict heat transport properties according to geometric structures and component materials. Based on a first-principles approach, namely, the Rayleigh method, here we develop an analytical way to calculate temperature-dependent (i.e., nonlinear) thermal conductivities of a composite with circular inclusions arranged in a periodic rectangular array. We focus on both weak and strong nonlinearity. As a result, we find that the temperature-dependence (nonlinearity) coefficient of the whole periodic composite can be larger than that of the nonlinear component inside this composite. Simulation results from finite element analysis show that the Rayleigh method can be also more accurate than the Maxwell-Garnett or Bruggeman effective medium approximations. As a model application, we further tailor the nonlinearity to design a thermal diode, for which heat flux along one direction is much larger than that along the opposite. This work provides a different theory for handling periodic structure with thermally responsive thermal conductivities, and it could be useful for designing thermal metamaterials with diverse properties including rectification.
  • The use of cooled axial conduction guarded probe for the measurement of
           transient heat flux by calibrating the unit step response
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Lijun Zhuo, Songhe Meng, Fajun Yi A novel water-cooled device with inserted thermocouple beneath the sensing surface is designed for long-duration heat flux measurement in harsh environments. The unit step response (USR) of the device, which is temperature-independent, is calibrated using a diode laser system. The heat flux is determined from the calibrated USR and measured temperature by solving an inverse heat conduction problem (IHCP). By calibration, the device achieves a high accuracy in measuring heat fluxes up to 800 kW/m2 The proposed procedure inherently accounts for all system parameters, including the thermocouple dynamics and the surface emissivity, which can decrease the experimental uncertainty. A detailed uncertainty analysis reveals the uncertainty of reconstructed heat flux can be significantly decreased with well-designed calibration tests and a prudent choice of the regularization parameter. Two examples for laser heat flux measurement are tested to validate the feasibility of the proposed method by comparing with the measurements from a reference sensor. The experimental results illustrate that the estimations are stable and accurate.
  • Analysis of heat transfer and material flow in hybrid KPAW-GMAW process
           based on the novel three dimensional CFD simulation
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Dongsheng Wu, Shinichi Tashiro, Ziang Wu, Kazufumi Nomura, Xueming Hua, Manabu Tanaka In this study, a novel electrode-arc-droplet-weld pool model considering the complex interactive phenomena of arc, keyhole and weld pool is developed to investigate heat transfer and material flow in hybrid KPAW-GMAW process, in which the double-ellipse heat source models, arc pressure models, arc shear stress models and electromagnetic force models are adopted. The arc, droplet, keyhole and weld pool are observed by high speed video camera. The temperature of droplet and weld pool are measured by thermal camera. The numerical and experimental results show that: In the KPAW process, two convective eddies exist inside the weld pool. The maximum temperature of the weld pool is firstly increased, then is decreased, and finally becomes stable. In the KPAW-GMAW process, the “Pull-Push” flow pattern helps to transport the molten metals and energy from the region near the GMAW arc to the region near the KPAW arc, resulting in the temperature increase of the molten metals at the top surface of the rear keyhole. The Marangoni force and arc shear stress are proposed to be the dominant driven forces for the “Pull-Push” flow pattern on the top weld pool surface between the two arcs, while the droplet impingement has minor influence on it.
  • The numerical modeling of the vapor bubble growth on the silicon substrate
           inside the flat plate heat pipe
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Yifan Cui, Huiyu Yu, Huajie Wang, Zhenyu Wang, Xiulan Yan Inside the flat plate heat pipes for the microelectronics packages, the micro scale boiling is a common phenomenon under the suddenly high heat flux. The internal vast vapor bubble nucleation and growth become a challenge for the stable operations. Due to the lack of the direct observations, the vapor bubble growth in early stage is still unclear. In order to study the initial bubble growth, the molecular dynamics models of water-silicon interfaces which have different sizes of simulation boxes were examined. The vapor bubble diameter growth rates (0.18 ± 0.02 × 106 mm/s) were calculated among the different sizes of simulation boxes. Since the lack of extra energy input, the initial vapor bubble can only expand to 45 nm diameter large (under 100 W/cm2 heat flux at 350 K initial temperature). The growth phenomena of 0.1 μm to 0.3 mm scale bubbles could be further modeled by the Mixture models. The observed bubble (bubble diameter between 10 μm and 0.3 mm) had a diameter growth of 0.71 ± 0.19 mm/s that was close to the Mixture model simulated one (0.75 mm/s). In addition, the ratio of the bubble volume growth rate to the bubble covered bottom area was about 7 ± 0.2 mm/s. By calculating the ratio between the growth rate of observed bubbles and volume of the simulated stable nucleation bubble, the bubble generation rate (3 × 1014 bubble/s mm2) under certain conditions might be estimated. Therefore, the whole process of bubbles growth could be deduced.Graphical abstractGraphical abstract for this article
  • Cross-helix corrugation: The optimal geometry for effective food thermal
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): F. Bozzoli, L. Cattani, S. Rainieri In the present paper, an innovative and effective heat transfer enhancement technique for food processing, cross-helix profile wall corrugation, is proposed and tested. In the food industry, the two most promising corrugation profiles are the transversal and single-helix ones because they both satisfy hygienic design principles. Among the available wall corrugation techniques, transversal corrugation allows for the highest heat transfer performance, and the spirally corrugated tubes guarantee the easiest manufacturing. For this reason, single-helix corrugated tubes are the most commonly employed in heat exchangers for food processing. The cross-helix profile presented in this work represents an intermediate solution between transversal and single-helix corrugation aimed at combining their positive aspects.One of the main goals of the current research is to identify an optimal geometry that maximises the heat transfer performance by limiting the pressure drop augmentation for this specific engineering application (i.e., food thermal processing). For this purpose, the effect of the geometrical parameters of the corrugation profile is investigated by varying two of the most influent quantities in terms of heat transfer performance and pressure drop: corrugation depth and corrugation pitch. Six pipes characterised by different cross-helix corrugations are tested. Their performance is evaluated by studying the forced convective heat transfer in the Reynolds and Prandtl numbers ranges (50–14,000 and 5–150, respectively), using ethylene glycol, water and a mixture of the two as the working fluids.The outcomes show that corrugation depth plays a crucial role in enhancing the heat transfer performance of the tested pipes. An optimal geometry is established, and correlations to describe its thermal and fluid flow behaviours are proposed. This optimal geometry shows superior performance to that of the most widely adopted types of corrugation. For the low/intermediate Reynolds number range (i.e., 200–2000), the efficiency of the proposed cross-helix profile is up to three times greater than that of the single helix and is also greater than that of transversally corrugated tubes. These outcomes make cross-helix a recommended option to be used in the design of optimised heat exchangers.Because the studied geometry is expressly developed for food industry application, a set of measurements is also performed in which apricot juice is adopted as the working fluid. The findings confirm the efficiency of the proposed correlations with non-Newtonian fluid foods and enable them to be extended to a wide range of real food industrial applications.
  • Numerical study on heat transfer behavior of wavy channel supercritical
           CO2 printed circuit heat exchangers with different amplitude and
           wavelength parameters
    • Abstract: Publication date: February 2020Source: International Journal of Heat and Mass Transfer, Volume 147Author(s): Zhe-Xi Wen, Yi-Gao Lv, Qing Li, Ping Zhou Performance enhancement of printed circuit heat exchanger (PCHE) is of great importance to the thermal efficiency improvement of supercritical CO2 Brayton cycle. In this paper, the heat transfer performance and flow characteristics of a sinusoidal wavy channel PCHE are numerically investigated. The effects of the amplitude and wavelength parameters are discussed under different mass flow conditions with inlet Re = 5210.8−13026.9 on the hot side. It’s found that the increase of amplitude and decrease of wavelength result in larger flow length and heat transfer area of the wavy channel, as well as higher heat transfer rate. The use of wavy channel instead of straight channel enhances heat transfer. Because of the complicated flow fields in the wavy channels affected by thermophysical property changes and centrifugal forces, the shapes and locations of high heat flux zones shift with different configurations. The secondary flow and heat transfer area change both contribute to the change of heat transfer characteristics. The resulting complicated heat transfer performance variation of different configurations are illustrated and discussed. Based on the overall performance evaluation results, the best performance is obtained with an amplitude of 3 mm and a wavelength of 50 mm or 75 mm.
  • Thermal performance of heat sinks with variable and constant heights: An
           extended study
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Kankan Kishore Pathak, Asis Giri, Biplab Das Heat sinks/fins are widely used in rapid heat removal processes like cooling of electronic devices, car radiators, transformer coils, nuclear reactors, etc. The thermal efficiency of the heat sinks mainly depends on the conductivity of the material used. In the present work, a comparative study is made on the thermal performance of heat sinks having variable and constant heights with respect to the bulk temperature, induced velocity, fin height/spacing/clearance, fin thermal conductivity and efficiency. A computational code based on SIMPLER algorithm is developed to solve the present problem. Results indicate that the variation of local Nusselt number against the flow direction shows higher values for the non-dimensional variable height heat sinks of 0.25 involving narrower fin spacing. It is also noted that consideration of finite conductivity of fin of 200 W/m-K and 75 W/m-K reduce the overall Nusselt number by 5.7% and 9.5% respectively while compared to an isothermal fin. Further, the use of variable height heat sinks coupled with a shorter fin height of 0.03 m indicates an improvement of thermal performance by around 225%.
  • Flow boiling instability characteristics in microchannels with porous-wall
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): L.X. Zong, G.D. Xia, Y.T. Jia, L. Liu, D.D. Ma, J. Wang In this work, a porous-wall microchannel heat sink was designed and fabricated, and the wall regions were etched with the micro pin fin arrangement instead of solid walls. The porous-wall can be divided into three regions: the densely/intermediate densely/sparely pin fin region with the fin gap of 5 μm/7.5 μm/10 μm, respectively. Flow boiling tests in porous-wall microchannels were carried out at mass fluxes of 250–510 kg/(m2·s) and heat fluxes of 120–720 kW/m2. The effects of the porous-wall on suppressing the flow instabilities and manipulating the boiling flow were studied, and different boiling flow behaviors of pressure drops and temperatures as well as corresponding flow patterns were measured and observed. The experimental results showed that: (1) With the porous-wall inter-connect effect, the premature ONB (Onset of Nucleate Boiling) can be occurred, the nucleate boiling flow in whole channel can be triggered in less than 2 ms, the boiling flow instability can be suppressed, and the duration of two-phase flow can be prolonged; (2) The boiling instabilities in porous-wall microchannels were classified into four flow modes, and the temporal behaviors of temperatures and pressure drops corresponding to each flow instability mode were observed and analyzed. (3) By PSD (Power Spectral Density) combined with WT (Wavelet Transform) analysis method, the coupled wall temperature oscillations in each instability type were decoupled into different instability sub-types at different amplitudes and timescales. Moreover, the analysis of ms-timescale flow instability induced by the flow pattern transition helps to better understanding the dominant influence of the porous-wall on the resulting temperature oscillations.
  • A correlation for heat transfer coefficient during stratified steam
           condensation in large flattened tubes with variable inclination and wall
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): William A. Davies, Pega Hrnjak This paper experimentally investigates heat transfer coefficient during stratified-flow condensation in a large flattened-tube steam condenser with non-uniform heat flux and wall temperature, and varying inclination angle. The heat transfer test facility is designed and built to provide local measurements of wall temperature; combined with a CFD model, it also provides local heat flux and heat transfer coefficient.The condenser test tube is that commonly used in air-cooled condensers for power plants. The steel tube has inner dimensions of 216 mm height × 16 mm width. In addition, tube inclination is varied from 0° to 38° downwards. The test facility is designed to match the conditions of an operating condenser, with low steam mass flux, realistic development of flow regimes and a large temperature glide on the cooling side.The results show that heat transfer coefficient along the tube wall follows the Nusselt condensation model, while heat transfer through the stratified liquid layer at the tube bottom is predominantly driven by laminar forced convection. Commonly-used correlations for heat transfer coefficient are unable to accurately predict the experimental results, so a new correlation is proposed. The new correlation takes into account heat transfer through the stratified liquid layer at the tube bottom as well as through the condensing film along the tube wall. Recommendations are made for situations where: (1) the wall temperature is known and (2) the wall temperature is unknown. Finally, a recommendation is made for combining the correlation in the stratified condensate layer with a local model for determining condenser capacity.
  • Viscous dissipation effects on the linear stability of
           Rayleigh-Bénard-Poiseuille/Couette convection
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Y. Requilé, S.C. Hirata, M.N. Ouarzazi We investigate how viscous dissipation changes the linear stability characteristics of Rayleigh-Bénard-Poiseuille/Couette mixed convection flows. In addition to the contribution of the vertical temperature gradient imposed in the external boundaries, thermal stratification is also a consequence of the volumetric heating induced by viscous dissipation. The governing equations for small perturbations after normal-mode expansion are solved numerically. Results showed that the most unstable perturbations are three dimensional longitudinal rolls. Viscous dissipation induced changes of the critical Rayleigh number and critical wave number at the onset of convection are determined as a function of the governing parameters Λ=GePe2 and Pr, where Ge,Pe and Pr are respectively the Gebhart number, the Péclet number and the Prandtl number. Two distinct modes of instability, with quite different characteristics, can occur. For moderate Λ, the linear instability properties are almost similar to Rayleigh-Bénard convection. When Λ is large enough, the viscous dissipation mechanism induced a strong destabilization and triggered instability even if heating is from above. A thermal energy budget analysis is proposed to understand the physical mechanism underlying the smooth transition between the two regimes of convection. Finally, the obtained results are discussed in connection with existing experiments and with hydrodynamic instability.
  • Experimental and numerical analysis on the surge instability
           characteristics of the vortex flow produced large vapor cavity in u-shape
           notch spool valve
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Liang Lu, Shuaihu Xie, Yaobao Yin, Shohei Ryu The u-shape notch, one of those representative types of throttling notch, is widely applied in the spools of hydraulic proportional directional valves. Because of its vacuum-suction nozzle-structural effect, the u-shape notch usually possesses relatively large flow capacity, while produces drastic cavitation as well. In this paper, the notch flow characteristics to form the large vapor cavity and its surge instability characteristics are discussed by experimental and numerical analysis. It is found that, instead of the vena contracta flow, but the notch vortex flow creates the more suitable low pressure condition for cavitation inception, with the helical-stream-trend to form the cavity spiral shape with clear vapor-liquid interface. Compared with the RANS turbulent model, the LES turbulent model associated with the multi-phase cavitation model reproduce the cavity volume and the spiral shape better, while the ISO surface of vapor volume fraction number equal to 0.6 is used to approximately represent the two-phase interface. In appropriate notch configurations, the vapor cavity shows surge instability, which couples the fluctuation of flow parameters with the mass transfer process. The notch flow resistance seems to play an important role on the surge behavior, since with the decrease of the notch depth, the harmonic oscillation turns into damped oscillation, while with the increase of the notch opening, the oscillation intensifies, and even gets disturbed from the downstream vapor shedding. The biggish notch flow resistance may suppress the surge instability, but reduce the flow capacity as well. It may be not easy to figure out an optimal notch structure only. However, using more number of larger flow resistance notches to replace few number of smaller flow resistance notches may be a positive suggestion.Graphical abstractGraphical abstract for this article
  • Receding liquid level in evaporator wick and capillary limit of loop
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Minwoo Lee, Chanwoo Park Macro/micro-scale structures of the evaporator wick of two-phase cooling systems have huge impacts on the flow resistance, thermal resistance, and capillary limit of heat transfer of the two-phase systems. In this study, various evaporator designs such as multilayer and monolayer evaporator wick bases, and porous and tubular wick posts were tested for the thermal performance in a loop thermosyphon (LTS) serving as a test platform. The monolayer wick built with mono-size sintered copper particles embedded in a single layer of a wire mesh was used to reduce the evaporator thermal resistance. The tubular wick posts were used to decrease the flow resistance of the liquid supply to the evaporator wick and eventually increase the capillary limit. The thermophysical and hydrodynamic properties (e.g. thermal resistance and permeability) of the monolayer wick were numerically determined for different liquid levels in the wick base, which was related to various boiling conditions (e.g. flooded, thin-film evaporation, and dryout). The measured thermal resistances were used to predict the liquid level in the wick and boiling conditions. The thermal performance and capillary limit of the LTS were predicted using a thermal-hydraulic network model. It was found from the numerical and experimental results that the evaporator with the monolayer wick base and tubular wick posts provides superior thermal performance such as low thermal resistances (0.097 K-cm2/W) and high capillary limit (309.8 W/cm2 for an elevation difference of 47 cm) as compared to the baseline evaporator using the multilayer wick base and porous wick posts.
  • Geometric optimization of a highly conductive insert intruding an annular
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): M.R. Hajmohammadi, E. Rasouli, M. Ahmadian Elmi Annular fins are abundantly applied in industry, especially for cooling curved surfaces such as the tube wall. However, it is well-known that the fin conductive resistance reduces the total cooling performance. Therefore, in this paper, geometric optimization is carried out to reach the maximum cooling performance of an annular fin intruded by a pathway of highly conductive materials (‘insert’). The optimization objective is to reach the minimum peak temperature of the annular fin that extracts heat with constant heat flux at the fin base. The fixed total volume of the fin, as well as the fixed total volume of insert, are considered as a constraint. The optimization process is in conjunction with a numerical solution to obtain the temperature field in the fin. The results show that the optimized insert results in considerable elevation of the fin performance by reducing the peak temperature (thermal resistance) of the fin. Finally, the effects of several parameters such as the conductance ratio and the Biot number on the optimal results are reported. It has been proved that increasing the conductance ratio and Biot number reduces the peak temperature.
  • Jet vortex heat transfer in turbulent air flow around a plate with a slit
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Dehai Kong, V.N. Afanasiev, S.A. Isaev, D.V. Nikushchenko Experimental study and numerical simulation of vortex heat transfer in turbulent air flow around the plate with permeable transverse rectangular ribs at qw = const have been made. Confusor, diffuser and constant cross-section slits as well as the constant gap between the plate and the lower wall of the rib are considered. Mean and fluctuation profiles of velocity and temperature along the midsection of the plate in the sections of the turbulent boundary layer are measured using both a Pitot–Prandtl microprobe with a microthermocouple and a Dantec Dynamics hot-wire anemometer. To calculate spatial separated flow of incompressible liquids, the Reynolds-averaged Navier–Stokes equations closed by five turbulence models are adopted. The use of the k-ε two-parameter model with the Kato–Lauder modification (SKE-KL) provides a satisfactory agreement between numerical predictions and experimental data. So this model is selected as the basic one. The influence of the throttling effect on the turbulent separated flow structure and relative heat transfer coefficient when changing the slit shape and size is analyzed. The integral characteristics including total heat transfer coefficient, hydraulic losses and thermal-hydraulic performance are also compared. It is shown that the presence of a slit can eliminate secondary separation zones on the plate and decrease recirculation flow regions behind a rib. The rib with a confusor slit has the highest thermal-hydraulic performance that is by 15% more than that of the solid rib.
  • The effect of twisted tape inserts on heat transfer and pressure drop of
           R1234yf condensation flow: An experimental study
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): B. Sajadi, M. Soleimani, M.A. Akhavan-Behabadi, E. Hadadi This paper deals with condensation flow inside plain and twisted tape inserted (TTI) tubes with diameter and length of 8.7 mm and 700 mm, respectively. R1234yf, identified as a viable alternative for R134a with low global warning potential (GWP), is examined as the working fluid. The heat transfer coefficient and the pressure drop of the flow are measured in different mass velocities and vapor qualities ranging 160–310 kg m−2 s−1 and 0.12–0.84, respectively. A well-equipped test rig consisting of a test condenser and other necessary equipment is employed to precisely adjust the test conditions. Experimental results for the plain tube are compared with some well-known correlations. As a result, Shah and Souza et al. equations are the most reliable equations to predict the flow heat transfer coefficient and its pressure drop, respectively. Different twisted tape inserts with three twist ratios of 6, 9, and 12 are exploited to study the effect of twisted tape geometry. The results indicate that up to 42% and 235% increment in the heat transfer coefficient and the pressure drop, respectively, is associated with implementing twisted tape inserts. In addition, it was shown that, among some correlations proposed previously in the literature, the experimental heat transfer coefficient and pressure drop in TTI tubes can be predicted by Akhavan Behabadi et al. and Hejazi et al. correlations with reasonable accuracy. According to the results, the twist ratio of 6 gives the highest increase in the heat transfer coefficient, while the ratio of 9 is associated with the highest overall enhancement ratio.
  • New analytical method for single-phase convective heat transfer and
           unified mechanism analyses on buoyancy-induced supercritical convective
           heat transfer deterioration
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Yalin Cui Single-phase convective heat transfer process can be regarded as a combination of two simultaneous processes, inner heat flux diffusion and absorption/release by equivalent inner heat sources, based on the analogy of convective heat transfer to conductive heat transfer. Inspired by this idea, a new analytical method for sing-phase convective heat transfer was developed from the perspective of synergy between equivalent inner heat source efficiency field (h′ field) and effective thermal conductivity field (λeff field). This new method employs hc and w′ to quantize the effects of h′ field and λeff field on convective heat transfer, making a quantitative and comprehensive analysis for most single-phase convective heat transfer phenomena possible. Subsequently, the buoyancy-induced convective heat transfer deterioration (HTD) of supercritical water under heating boundary conditions were analyzed using this new method. It was found that the supercritical HTD for upward flow is caused by the decline of both the λeff and h′ fields, especially in the near-wall regions. While, the supercritical HTD at the top part of the wall for horizontal flow is due to the fact that the high-value part of the h′ field is moved downward by a pair of vortices induced by buoyancy. Thus, the inner heat fluxes released from the top part of the wall have to be diffused through a much longer distance, leading to the HTD.
  • Solidification behaviors and parametric optimization of finned shell-tube
           ice storage units
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Chengbin Zhang, Qing Sun, Yongping Chen The present paper reports on a numerical study of the ice storage process in finned shell-tube ice storage (STIS) units, with a focus on the special solidification behavior using water as the phase-change material (PCM). The proposed model is experimentally verified using an energy-discharging process in an ice storage unit. The effects of natural convection and buoyancy reversal on the solidification behavior are examined and investigated. Moreover, the Taguchi method is utilized to optimize the fin geometry of STIS units. The results indicate that the natural convection and buoyancy reversal are negatively correlated with the ice storage performance. An increase of the superheat factor leads to the enhancement of the buoyancy reversal intensity, which is not conducive to the acceleration of the solidification rate. In addition, the increases in fin height, fin width, and fin number are positively correlated with ice storage performance. It is demonstrated that the fin height is the dominant factor affecting the overall ice storage performance, and it is independent of the superheat factor. From the perspective of trade-off between ice storage rate and ice storage capacity, the optimal fin parameters for the STIS unit are fin height H = 40 mm, fin number N = 10, fin width Δ = 3 mm for engineering applications.
  • The stagnation point heat transfer under partially-developed submerged
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Barak Kashi, Herman D. Haustein Laminar jet impingement is an efficient method for heat transfer processes, though much of its hydrodynamics and the resulting convection are still not fully understood. As previously shown, stagnation-point heat transfer (Nu0) depends directly on the near-axis radial acceleration (A0) varying strongly with nozzle diameter (d), normalized nozzle length (L), normalized nozzle-to-plate spacing (H) and flow rate (Re), therefore a general expression is here developed for this key parameter.Through streamline-bending analysis it was identified that A0 can be derived from the characteristics of the velocity profile arriving at the point of transition from free jet flight to stagnation flow (at zw). This analysis also led to the identification of the curvature of the velocity profile in the jet-core as the key factor dictating A0, over a domain defined by a new characteristic scale Rc. Examination of this curvature, resolves the apparently contradicting trends in the literature for A0′s dependence on flight distance. Moreover, it explains the occurrence of maximal heat transfer, when h is set around the potential core length.Building on the theoretical analysis, an explicit, yet universal, model for Nu0 was developed in terms of nominal geometry and flow rate, rather than relying on the often-unknown arrival profile, and validated against simulations over a wide range of conditions (0.003 ≤ L, 0.001 ≤ H, 250 ≤ Re ≤ 2000). Therein, this model pin-points the location of the maximal heat transfer for any issuing profile, enabling efficient design and optimization.Finally, identifying zw as the stagnation-flow characteristic scale instead of d, enabled extension of an existing wall-approach model to include partially-developed profiles and longer flights. Then requiring the model′s conformity to previous theory gave an explicit expression for zw – the lower-bound of H⋅Re still permitting heat transfer analysis assuming decoupling between the nozzle and wall flows.
  • Compound heat transfer enhancement of helical channel with corrugated wall
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Morteza Khoshvaght-Aliabadi, Amir Feizabadi Newly, the use of corrugated structures in heat exchange devices has become a useful technique due to the combined merits of extended surfaces and turbulators. However, employing of this technique in curved channels is very scarce. To this aim, as a new passive compound technique, the periodical corrugated structure is proposed to enhance the overall hydrothermal performance of a helical channel with square cross-section. Firstly, calculated results for the smooth model are compared with existing empirical correlations in the literature to explore the reliability and accuracy of the current analysis. Secondly, the corrugated structure on each side (upper, lower, inner, and outer) as well as opposite sides (upper-lower and inner-outer) of the helical channel is tested individually. It is found that corrugating the side walls of the helical channel prevents the development of thermal boundary layers through the flow direction and changes continuously the location and strength of generated secondary flows and velocity contours, leading to more uniform temperature. Thirdly, three different levels of corrugation-amplitude (A = 0.8, 1.6, and 2.4 mm) and coil-diameter (D = 50, 100, and 150 mm) are considered. At the studied range of Reynolds number (100 ≤ Re ≤ 500), the best enhanced model is the case of upper-lower at A = 2.4 mm and D = 100 mm, and the maximum performance index of 1.46 is recorded for water flow through this model at Re = 400.Graphical abstractGraphical abstract for this article
  • Compact heat exchangers – Design and optimization with CFD
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Chamil Abeykoon Heat transfer is one of the key aspects of machineries, devices and industrial processes for maintaining their functionality and also for achieving better product quality. Hence, heat exchangers of different types and sizes are used in these applications with the purpose of removing the extra process/device heat to maintain the desirable working temperatures. However, the size of a heat exchanger is a major consideration for any type of process/device as it decides the space requirements (i.e., the size) of the machine/device or the processing plant. At first, this study aims to investigate the design procedure of a heat exchanger theoretically and then its performance will be analyzed and optimized using computational fluid dynamics. For the design purposes, a counter flow heat exchanger was considered and its length was theoretically calculated with the LMTD method while the pressure drop and energy consumption were also calculated with the Kern method. Afterwards, a computational model of the same heat exchanger was implemented with ANSYS and then this model was extended to six different models by altering its key design parameters for the optimization purposes. Eventually, these models were used to analyze the heat transfer behavior, mass flow rates, pressures drops, flow velocities and vortices of shell and tube flows inside the heat exchanger. Theoretical and CFD results showed only a 1.05% difference in terms of the cooling performance of the hot fluid. The axial pressure drops showed positive correlations with both the overall heat transfer coefficient and pumping power demand. Overall, the results of this study confirms that CFD modelling can be promising for design and optimization of heat exchangers and it allows testing of numerous design options without fabricating physical prototypes.
  • Flow behavior and heat transfer characteristics in Rayleigh-Bénard
           laminar convection with fluid-particle interaction
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Mufeng Chen, Xiaodong Niu, Peng Yu, Haruhiko Yamasaki, Hiroshi Yamaguchi The present study experimentally and numerically investigates the Rayleigh-Bénard (R-B) laminar convection of a Newtonian fluid in a square cavity heated from the bottom wall at the initial conditions of constant temperature field and stationary flow field over the range of Rayleigh number Ra ≤ 4 × 104. The effect of a freely-moving particle in the cavity on the flow pattern and heat transfer characteristics is discussed. When the stable multi-stability patterns coexist, i.e. Ra is beyond a certain critical value, the final flow pattern can be manipulated by adjusting the initial position of the particle. The bicellular mode is established if the particle is located at the bottom center of the cavity while the unicellular mode is established if the particle is away from the center. The present results demonstrate that at the same Ra, the thermal performance is mainly determined by the flow pattern but not the presence of a particle. However, one can control the final flow pattern for R-B convection by adjusting the initial position of the particle, which consequently determines the thermal performance.
  • Wavy falling film of nanofluid over a vertical plate considering
           nanoparticle migration
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Ze Cheng, Jie Peng In this investigation, the wavy falling film flow over a vertical plate is studied with the effects of nanoparticle migration on the film flow dynamics being considered by the integral-boundary-layer (IBL) method. Both the Brownian motion and thermophoresis are included. The average heat transfer rate is compared for different nanoparticle fractions and different ratios of Brownian diffusion and thermophoretic diffusion. Both cooling and heating problems are discussed. The particle migration direction, which may lead to the opposite role in the flow dynamics, is controlled according to different temperature boundary conditions. The results show that particle migration plays an important role in regulating the intensity of solitary-like waves on the film by causing the distribution of viscosity and density. The particle migration affects the film heat transfer by causing the distribution of thermal conductivity and regulating the average thickness.
  • An experimental investigation on the dynamic ice accretion and unsteady
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Yang Liu, Kai Zhang, Wei Tian, Hui Hu In the present study, a comprehensive experimental study was conducted to evaluate the effects of initial ice roughness formed around the leading-edge of an airfoil model on the dynamic ice accretion and unsteady heat transfer processes over the airfoil surface. The experimental study was performed in the Icing Research Tunnel at Iowa State University, Two airfoil models with the same airfoil shape were manufactured by using a rapid protype machine for a comparative study, i.e., one test model was designed to have embedded initial ice roughness around the airfoil leading-edge and the other model having smooth airfoil leading-edge as the comparison baseline. During the experiments, while a high-speed imaging system was used to record the early-stage icing morphologies over the airfoil surfaces with and without the initial leading-edge roughness, an infrared (IR) thermal imaging system was also utilized to map the corresponding surface temperature distributions over the airfoil surfaces to quantify the unsteady heat transfer and dynamic icing, i.e., phase changing, processes under different test conditions. It was found that, the initial ice roughness formed around the airfoil leading-edge would affect the characteristics of local airflow, impingement of supercooled water droplets, collection and transport of impacted water mass, unsteady heat transfer and subsequent ice accretion processes dramatically. The initial ice roughness formed around the airfoil leading-edge would redistribute the impacted water mass, with more impacted water mass being captured and frozen over the roughness region. In addition, the initial ice roughness was also found to produce span-wise-alternating low- and high-momentum pathways (LMPs and HMPs, respectively), which can significantly affect the convective heat transfer and subsequent ice accretion processes over the airfoil surface.
  • Heat and mass transfer during a sudden loss of vacuum in a liquid helium
           cooled tube – Part II: Theoretical modeling
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Shiran Bao, Nathaniel Garceau, Wei Guo A sudden loss of vacuum in particle accelerator beamlines and other cryogenic systems can lead to substantial equipment damage and possible personnel injuries. Developing a clear understanding of the complex dynamical heat and mass transfer processes involved following a sudden vacuum break is of great importance for the safe operation of these systems. Our past experimental studies on sudden vacuum break in a liquid helium cooled tube revealed a nearly exponential slowing down of the propagating gas front. However, the underlying mechanism of this slowing down is not fully explained. In this paper, we discuss a theoretical framework that systematically describes the gas dynamics, heat transfer, and mass deposition of the propagating and condensing gas inside the helium-cooled tube. The experimentally observed apparent gas-front propagation, measured as the abrupt temperature rise by the thermometers installed along the tube wall, can be well reproduced by the model simulation. We also show that following the gas front, the mass deposition rate of the gas on the tube inner wall approaches a constant. The extension of this nearly constant gas deposition zone is the key to understand the observed exponential slowing of the gas propagation. Our model also allows us to gain valuable insights about the growth of the frost layer on the tube inner surface. This work paves the way for a theoretical understanding of the physical processes involved during vacuum break in accelerator beamlines.
  • Numerical modelling of radiation absorption in a novel multi-stage
           free-falling particle receiver
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Apurv Kumar, Wojciech Lipiński, Jin-Soo Kim A novel multi-stage free-falling particle receiver design is proposed to improve the simple free-falling concept by enhancing the hydrodynamic stability and improving the radiation absorption of the particle curtain. The multi-stage design arising from repeated re-initialisation of the particle curtain by using intermediate troughs in the receiver results in an increased average volume fraction and residence time of the particles. The present work numerically solves the mass, momentum and radiative transfer equation for an isothermal two dimensional Eulerian–Eulerian particle–gas multiphase flow equations to estimate the absorption characteristics of the particle curtain. The multi-stage receiver concept significantly improves the absorptance of the curtain and reduces the reflection losses by over 50%. The reflection losses are seen to be insensitive to increase in size of the receiver making the multi-stage concept highly scalable.
  • Solidification with crystallization behavior of molten blast furnace slag
           particle during the cooling process
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Jie Gao, Yanhui Feng, Daili Feng, Zhen Zhang, Xinxin Zhang The centrifugal granulation technique has been considered for the recovery of waste heat retained in molten blast furnace slag while simultaneously obtaining high value slag particles for cement auxiliary materials. During granulation the high wind speed is expected to acquire high vitreous slag particles formed by centrifugal force of the atomizer, but result in significant energy consumption and low-grade heat of the cooling air. To address this problem, we established a two-dimensional symmetrical model to describe the crystallization behavior of blast furnace slag droplets by the enthalpy method via self-programming. The radiation heat transfer between slag particle and the wall was considered as well as non-isothermal solidification, including a narrow temperature interval of crystallization. The results display the evolutions of the local cooling rate and crystal phase content distribution. The effects of the diameter, initial temperature of the slag particle, wind initial temperature and wind speed are also discussed. Furthermore, two correlations of the average cooling rate and final crystal phase content with dimensionless parameters were developed respectively, to predict slag quality under various operational conditions.
  • A comprehensive geometrical study on an induced-charge electrokinetic
           micromixer equipped with electrically conductive plates
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Morteza Nazari, Po-Ya Abel Chuang, Javad Abolfazli Esfahani, Saman Rashidi In this paper, a numerical study is performed on an induced-charge electrokinetic micromixer. The electrically conductive plates are installed inside the micromixer to induce vortices that improve the mixing index of the system. A comprehensive geometrical study is performed on this micromixer and the effects of various parameters are investigated. These parameters include the mounting, length, orientation, position, arrangement and number of the conductive plates, and the intensity of the external electric field. To benchmark the accuracy of the numerical model, the simulated results are compared and agree well with existing experimental and numerical data in the literature. The results show that a mixing efficiency of 99.6% can be achieved by placing two 5° angle conductive plates near the upper and lower walls and one 5° angle conductive plate at the center of the micromixer. It is also observed that the mixing performance increases with increasing conductive plate length. The mixing efficiency can be improved from 67.2% to 94.3% by increasing the plate angle from 0° to 40°. Combining these optimizations, close to 100% mixing efficiency can be achieved by placing three staggered and tilted conductive plates at an angle of 5°.
  • Experimental study on the thermal behavior of RT-35HC paraffin within
           copper and Iron-Nickel open cell foams: Energy storage for thermal
           management of electronics
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Tauseef-ur- Rehman, Hafiz Muhammad Ali In this paper, experimental investigations are carried out to study the thermal performance of metallic foams impregnated with phase change material (PCM) based heat sinks for thermal management of electronics. Herein, RT-35HC with melting point 34–36 °C is chosen as PCM and copper foam1 (95% porosity), copper foam2 (97% porosity) and Iron-Nickel foam (97% porosity) are used as thermal conductivity enhancer. Various configurations of the heat sink are investigated for 5400 s each for charging and discharging processes under heat flux 0.8–2.4 kW/m2 for PCM volume fractions 0.0, 0.6, 0.7 and 0.8. Results revealed that copper foam-based heat sink showed 5–6 °C less base temperature as compared to that of Iron-Nickel foam. While investigating the effect of foam porosity, copper foam with lower porosity (95%) has shown 11% less base temperature at the end of the charging cycle. It was also noticed that the maximum thermal conductivity enhancement of PCM was found to be 34 times for 95% porosity copper foam with the latent heat reduction of 37%. Copper foam1-PCM composite posed the maximum enhancement in operation time of heat sink 7.9 times more as compared to that of the empty aluminum heat sink. Copper foam -PCM composite with 95% porosity of foam with 0.8 vol fraction of PCM is best recommended configuration for the present experimental study.
  • Effect of uniform external magnetic-field on natural convection heat
           transfer in a cubical cavity filled with magnetic nano-dispersion
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Desh Deepak Dixit, Arvind Pattamatta Heat transfer in magnetic nano-particle dispersion can be influenced by the presence of external magnetic-field. This paper presents an experimental investigation on effect of external uniform magnetic-field on natural convection heat transfer in magnetite and iron nano-dispersion in a differentially heated cubical cavity. The experiments are conducted between the Rayleigh number range of 4.23×105 to 1.0×107. The study includes experiments and discussion on the corroborating and suppressing effects of thermo-magnetic convection induced by the external magnetic-field on the natural convection heat transfer. Additionally, this study also reports the experimental results and pertinent explanation on the directional effect of magnetic-field on the heat transfer in magnetite and iron nano-dispersion. The paper quantitatively presents the extent of heat transfer depreciation/enhancement in different orientations of the cavity in the presence of magnetic-field. The study also explores the effect of particle volume fraction in magnetic fluid on heat transfer in each case.
  • Effects of turbulator with round hole on the thermo-hydraulic performance
           of nanofluids in a triangle tube
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Cong Qi, Fan Fan, Yuhang Pan, Maoni Liu, Yuying Yan For investigating the thermal and hydraulic characteristics of water-based SiO2 nanofluids in a triangular tube with different turbulators, an experimental system has been designed and verified in this paper. The effects of different round hole diameters (d = 3 mm, 4 mm, 5 mm) and round hole pitch-rows (l = 5 cm, 10 cm, 15 cm) of perforated turbulators on the thermo-hydraulic characteristics are researched. Meanwhile, the influences of Reynolds numbers (Re = 400–8000) and nanoparticles mass fractions (D-I water, ω = 0.1%, 0.3%, 0.5%) are also studied. These experimental results show that, under the same circumstance, the nanofluids in the triangular tube with ω = 0.5% have the largest positive influence on the heat transfer enhancement ratio which is up to 16.73%. For a comprehensive study of the flow and heat transfer, thermal efficiency (comprehensive performance index) and exergy efficiency are adopted. It can be found that the larger the diameter and the smaller the pitch-row of the holes is, the greater the comprehensive evaluation index can be. In addition, all working conditions exhibit the superior exergy efficiency. The highest exergy efficiency can be got when Re = 6000 and ω = 0.5%.Graphical abstractThe experimental system: (a) Schematic diagram. (b) Physical diagram.Graphical abstract for this article
  • Important properties of turbulent near-wall flows which are not accounted
           by modern rans models
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): B.P. Golovnya Hypothesis based on experiments of various authors which explains the origin of many difficulties arising in the development of RANS models was proposed in the paper. A model design method based on this hypothesis is proposed. Models based on this method are much simpler than traditional ones. In addition, these models demonstrate the possibilities that are inaccessible to traditional models - they reproduce the regularities of cascade energy transfer, results of dissipative scales calculations correspond to the experiments. At present the method is verified by calculations of forced turbulent flows in boundary layers and pipes and channels.
  • Experimental investigation on convective heat transfer of hydrocarbon fuel
           in circular tubes with twisted-tape inserts
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Song Feng, Xiang Cheng, Qincheng Bi, Hui Pan, Zhaohui Liu The convective heat transfer of a kerosene-type hydrocarbon fuel was experimentally investigated in electrically heated horizontal circular tubes with twisted-tape (TT) inserts, in the fuel bulk temperature range of 288.0 ~ 873.0 K, at supercritical pressures. The effects of the system pressure, heat flux, buoyancy, thermal acceleration and twist ratio were investigated with a wide range of supercritical conditions. The sharp variation in the thermal properties with respect to temperature was the key factor influencing the heat transfer. Normal heat transfer, heat-transfer enhancement and heat-transfer deterioration occurred in the dimensionless position. The difference between the top and bottom wall temperatures in plain and TT tubes was investigated. Gr/Re2 was calculated and used to predict the buoyancy effects, and Kv was calculated to examine the thermal acceleration effects. The inner wall temperature and heat-transfer coefficients were compared for plain and TT tubes. The circular tube with TT inserts was shown to enhance heat transfer. Finally, a well-predicted empirical correlation of the Nusselt number was proposed for horizontal flow heat transfer in TT tubes.
  • Liquid-liquid interfacial instability model for boiling refrigerant
           transition by pool boiling of immiscible mixtures
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Osamu Kawanami, Kazuki Matsuhiro, Yasuhiko Hara, Itsuro Honda, Naohisa Takagaki Boiling heat transfer using immiscible liquid mixtures is an innovative cooling method for electronic devices operated at high heat flux density. Immiscible liquid mixtures discussed here are composed of more-volatile liquid with higher density and less-volatile liquid with lower density such as combination of FC-72 and water. In the case of pool boiling in a vessel using appropriate composed ratio of immiscible liquid mixtures, more-volatile liquid on the heating surface is boiled and as the heat flux increases, the more-volatile liquid reaches the critical heat flux. Subsequently, the less-volatile liquid is replaced with the more-volatile liquid and moves onto the heating surface, and this liquid is started boiling. This phenomenon is called a boiling refrigerant transition (BRT) and is an important feature of pool boiling by immiscible mixtures. To clear the phenomena of BRT in pool boiling by immiscible mixtures, the experiments under the conditions of various heights of more-volatile liquid layer and various mixture composed ratio by using several combinations of immiscible mixtures are carried out. And a new model derived by Kelvin-Helmholtz instability at the liquid-liquid interface is proposed for the occurrence of BRT. The unique heat transfer characteristics of the immiscible liquid mixtures were obtained from the experimental results; occurrence of BRT depends on the height of more-volatile liquid, and the characteristics after BRT is corresponding to the characteristics of pure less-volatile liquid. Experimental results including data from past literatures agreed well with newly proposed model.
  • Local heat transfer coefficient during stratified flow in large,
           flattened-tube steam condensers with non-uniform heat flux and wall
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): William A. Davies, Pega Hrnjak Steam condensation heat transfer coefficient (HTC) in a large, flattened tube with non-uniform heat flux and wall temperature, and variable inclination angle is determined experimentally. The condenser tube is that typically used in an air-cooled condenser for power plants. The steel tube has an elongated-slot cross section with inner dimensions of 216 × 16 mm. Water vapor and liquid flow co-currently through a 5.7 m long air-cooled conditioning section, followed by a 0.12 m long water-cooled test section. The long conditioning section creates conditions in the test section that mimic the conditions in an operating condenser – allowing for the realistic development of flow regime and void fraction. HTC is then determined in the water-cooled section. The water-cooled section is designed as a crossflow heat exchanger to match the temperature and heat flux conditions of an air-cooled condenser. Visualization sections at the tube inlet and outlet allow determination of flow regime and void fraction. The flow is found to be stratified for all conditions. Tube inclination angle is varied from 0 to 38° downwards. Inlet quality in the water-cooled section ranges from 0 to 0.74. HTC is found to increase by more than 400% along the condenser height. In addition, inclination angle, wall-steam temperature difference, inlet water-steam temperature difference, water temperature glide and vapor quality are all found to affect the condensation HTC.
  • Numerical and experimental investigations of hybrid nanofluids on
           pulsating heat pipe performance
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): M. Zufar, P. Gunnasegaran, H.M. Kumar, K.C. Ng This study investigates the thermal performance of a four-turns Pulsating Heat Pipe (PHP) using a weight concentration of 0.1 wt% Al2O3-CuO hybrid nanofluid, 0.1 wt% SiO2-CuO hybrid nanofluid and water both experimentally and numerically. The start-up pulsations, average evaporator temperatures, thermal resistance, two-phase flow, and non-linear temperature analysis were evaluated with respect to heating power and filling ratio of 10–100 W and 50–60%, respectively. Stability measurement and characterization of thermal conductivity and viscosity properties of hybrid nanofluids were determined. From the experimental results, the thermal resistance SiO2-CuO hybrid nanofluid exhibited was the lowest, i.e. 57% lower than that of water, followed by the Al2O3-CuO hybrid nanofluid, i.e. 34% lower than that of water at the heat input and filling ratio of 80 W and 60%, respectively. Nevertheless, the thermal conductivity and viscosity of Al2O3-CuO hybrid nanofluid were higher than those of SiO2-CuO hybrid nanofluid. The increased viscosity found in Al2O3-CuO hybrid nanofluid would hinder the fluid transportation in PHP, thus augmenting the thermal resistance. Meanwhile, the hybrid nanofluids were able to achieve start-up pulsations earlier and they required lower heating power to reach start-up pulsations as compared to water. At low heating power (below 30 W), the differences in average evaporator temperatures for hybrid nanofluids and water were very small. However, at higher heating power (above 30 W), the differences were significant. The numerical results compared well with those earlier experimental work, thus indicating the reliability of the current numerical simulation.
  • Reacting gas-surface interaction and heat transfer characteristics for
           high-enthalpy and hypersonic dissociated carbon dioxide flow
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Xiaofeng Yang, Yewei Gui, Guangming Xiao, Yanxia Du, Lei Liu, Dong Wei Hypersonic carbon dioxide reacting gas-surface interaction occurs on the heat shield of high-speed Mars entry capsules, which has great influences on the heat transfer characteristics. Based on hypersonic reacting flow solver with complex surface thermochemistry, the hypersonic chemical non-equilibrium flow with oxygen/carbon gas mixture was numerically simulated, and the interaction between non-equilibrium flow and surface reactions was numerically analyzed to reveal the mechanism of aerodynamic heating from surface thermochemistry. Numerical results of catalytic effects show that the near-wall thermochemical behaviors are essentially dominated by the near-wall diffusion and chemical reactions. Various surface reactions alter the flow structure in the boundary layer, and generate different aerodynamic heating patterns. Results from ablating simulations indicate that the ablating surface can induce additional near-wall diffusion and injection energy though their influence on the thermal boundary layer structure is neglectably small. The modeling of reacting gas-surface interaction can be of benefit to promoting the fidelity and precision of aerodynamic heating with complex surface thermochemistry.
  • Ar-CO-liquid steel flow with decarburization chemical reaction in single
           snorkel refining furnace
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Shifu Chen, Hong Lei, Meng Wang, Bin Yang, Weixue Dou, Lishan Chang, Hongwei Zhang As a new style refining equipment developed from the traditional RH furnace, Single Snorkel Refining Furnace (SSRF), which is also called as single snorkel RH, is widely used for producing ultra-low carbon steel. However, the effect of CO gas on fluid flow and decarburization is not reported in the existing literatures. Based on the Eulerian-Eulerian approach, a two-way coupling mathematical model considering CO gas is proposed to investigate the coupling phenomenon of Ar-CO-liquid steel flow and decarburization in SSRF. And the industrial experimental data is employed to validate the numerical result. In comparison with the one-way coupling model, the numerical result predicted by the two-way coupling model is closer to the industrial experimental data. The CO mole number, which is generated by the overall decarburization process, is about 3 times the argon mole number blown into the ladle, and the CO generation rate is greater than argon blowing rate at the first 12 min. Because of the stirring effect of CO gas, there are the more complex fluid flow, the stronger mass transfer, the greater decarburization rate and the lower carbon mass concentration in the liquid steel during decarburization. Besides, the Ar plume area predicted by the two-way coupling model is larger and it is closer to the center line of the snorkel. Therefore, the effect of CO gas on the fluid flow cannot be ignored and the two-way coupling model can describe the metallurgical phenomena in SSRF more precisely.
  • Study on the influence of hydro-thermal-salt-mechanical interaction in
           saturated frozen sulfate saline soil based on crystallization kinetics
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Jing Zhang, Yuanming Lai, Jifeng Li, Yanhu Zhao The freezing of saturated saline soil is a dynamic hydro-thermal-salt-mechanical (THSM) interacting process. One-side freezing experiment of saturated sulfate saline soil in an open system with no-pressure water supplement is carried out. The coupling mechanism of water and salt migration and the soil deformation in the freezing process has been investigated by the one-side freezing experiment. Based on the crystallization kinetics theory, a hydro-thermal-salt-mechanical coupled mathematical model for saturated frozen sulfate saline soil with the effect of phase change is proposed. Moreover, the influence of solute on the physical and mechanical properties of soil during the freezing process is considered. To solve the nonlinear equations, the finite element algorithm is applied to solve the general form of governing equations. Finally, numerical simulation is implemented with the assistance of COMSOL. Validation of the model is illustrated by comparisons between the simulation and experimental results. From this study, it is found that, (1) the phenomenon of macroscopic crystallization can be well illustrated by the microscopic crystallization kinetics theory on the basis of the concepts of the water activity and the solution supersaturation. (2) The pore pressure due to the effect of phase change is main driving force for water and salt migration as well as the deformation of porous medium. It is concluded that the positive pore pressure is the main factor for soil deformation, and the negative pore pressure is the driving force for water migrates to the frozen zone. (3) Salt migrates with water and is rejected into the unfrozen water in the process of ice formation, and the rate of salt rejection gradually increases with the decrease of cooling rate. Therefore, salt crystals with layer distribution are formed in the frozen zone during the freezing process, and the largest salt crystals distribution zone is formed near the freezing front due to the effect of solute diffusion. (4) The calculated results are well agreement with the experimental data, demonstrating that the proposed hydro-thermal-salt-mechanical coupling model can well clarify the mechanism of heat and mass transfer in saturated frozen sulfate saline soil, and predict the deformation due to the effects of frost heave and salt expansion.
  • Assessment of performance of subgrid stress models for a LES technique for
           predicting suppression of turbulence and heat transfer in channel flows
           under the influence of body forces
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Valerij I. Artemov, Maksim V. Makarov, Konstantin B. Minko, Georgij G. Yankov The main purpose of this work was to assess the performance of subgrid stress models for large eddy simulation (LES) of the flow and heat transfer of a conductive liquid simulating a molten salt (Pr = 4.1) in a square duct under the influence of a transverse magnetic field and an upward flow of air in a vertical heated pipe under a strong influence of buoyancy. An analysis of these problems is important when choosing the most appropriate subgrid-scale LES model for calculating the flows of an electrically conductive liquid under the combined influence of a magnetic field and buoyancy forces. Four subgrid-scale (SGS) models were verified: the Smagorinsky model with damping function (SMP), a coherent structure model (CSM), a WALE model and a hybrid model based on the equation for turbulent kinetic energy (KDES). For magnetohydrodynamic (MHD) flow in the duct, computations were performed in a domain with periodic inlet-exit boundaries and in a domain corresponding to the entrance region of a duct with a transverse magnetic field. Mixed convection of the air in the vertical heated pipe was simulated only in the domain with periodic boundaries. The results are compared with available data of direct numerical simulations (DNS).For MHD flow in the duct, the best predictions of DNS data for the average and fluctuating velocity components at Ha=21.2 and Re=5602 were obtained with the CSM and WALE models. The skin-friction and heat transfer coefficients are well known to have a minimum as Ha increases due to turbulence suppression by the magnetic field. The SMP and KDES models predict a minimum at Hadip≈22, whereas the CSM and WALE models predict a minimum at Hadip≈30 for Re=5602. The DNS data marked these values as the lower and upper boundaries of the complete turbulence suppression region for the same Reynolds number.For mixed convection of the air upward flows in a circular heated pipe at Re=5300, the CSM and WALE models showed weaker suppression of turbulence due to buoyancy forces when compared to the DNS results. The results of calculations of skin-friction and heat transfer coefficients performed with the help of the SMP and KDES models are much more coincident with the DNS data.
  • Numerical investigation of synthetic jets driven by thermoacoustic
           standing waves
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Geng Chen, Gopal Krishan, Yi Yang, Lihua Tang, Brian Mace We have carried out a preliminary study of the physical processes leading to the formation of a jet into external quiescent surroundings driven by thermoacoustic standing waves. The standing waves are initiated in a thermoacoustic engine (TAE) utilizing the thermoacoustic effect, and the synthetic jet is produced via a jet ejector where a sudden change in the cross-section is employed. We investigate the characteristics of the proposed synthetic jet actuator using both reduced-order network model and computational fluid dynamics (CFD) simulations. The network technique, which is based on linear thermoacoustic theory, can predict the onset of thermoacoustic instability in the frequency domain. The CFD code solves the fully coupled nonlinear compressible flow equations and enables the time-domain analysis of complex flow patterns, which facilitates comprehension of the jet formation process. Both theoretical analysis and numerical simulations reveal that spontaneous, self-excited oscillations inside the TAE will happen when the temperature ratio is greater than the onset temperature ratio for thermoacoustic instability. CFD simulations further identified the transition from no jet to a clear synthetic jet, which determines the onset temperature ratio for jet formation and the threshold value of a non-dimensional parameter. Finally, we carried out a parametric study to investigate the influence of resonator length and orifice diameter on the onset characteristics as well as other performance parameters including the acoustic intensity, space-averaged mean momentum flux, space-averaged velocity and the jet effectiveness. The proposed thermoacoustically-driven synthetic jet actuator may outperform conventional actuators driven by a piston, loudspeaker or piezoelectric transducers on occasions where the surface temperature is high, and therefore has the potential to be utilized for self-cooling purposes.
  • Dynamics of particle wetting in wet granulation: Micro-scale analysis
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Elham Heidari, Mohammad Amin Sobati, Salman Movahedirad Particle wetted surface area affects the probability of particles aggregation in the fluidized bed wet granulation process. Modeling the dynamics of binder spreading over particles and binder evaporation can help to determine the wetted area in time. To this end, a possible chain of events in the particle/droplet level has been proposed to reveal the effect of binder spreading and evaporation on granulation. Then, a second-order model has been introduced based on the key points of spreading, including the initial spreading radius, d∗, and the equilibrium radius. The model is compatible with conventional laws that R(t)∝t0.5 in the inertia-dominant regime and R(t)∝t0.1 in the viscous dominant regime. The binder evaporation has been considered in two situations including the simultaneous evaporation with spreading and evaporation after spreading. In the latter situation, the evaporation model of a sessile droplet on a substrate was employed while in the former situation the evaporation model has been merged with the proposed spreading model. This model has been validated by experimental data and two available theoretical models of spreading. In addition to simplicity and no need for tuning parameter, the present model shows the acceptable accuracy in comparison with the other models. Finally, the effects of impact velocity, equilibrium contact angle, droplet diameter, and temperature on the dynamics of spreading diameter have been investigated using the present model.Graphical abstractSequence of events in fluidized bed wet granulation.Graphical abstract for this article
  • Energy flow-based method for analysis and optimization of evaporative
           cooling and ventilation systems
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Fang Yuan, Wengang Dong, Guangfeng Shen, Yi Li, Wei Liu Physical and mathematical models significantly affect the ease of system analyses and optimization. This contribution presents a modified thermal resistance model for an evaporative cooling process and establishes an energy flow model analogous to an electrical circuit for an indirect evaporative cooling and ventilation (IECV) system based on the overall energy transport. The system modeling equations based on Kirchhoff's laws are a set of linear algebraic equations that characterize the relationships between each component in the system. They are applied as system constraints in the Lagrange multipliers method to optimize the design. The optimization minimizes the total thermal conductance for a fixed cooling capacity and total circulating water mass flow rate. The solutions of the optimization equations for a typical IECV system give a set of Pareto frontiers that reflect the trade-off between the thermal conductance and the mass flow rate, which represent the investment cost and the operating cost. Optimizations with various cooling capacities, indoor temperatures and ambient air conditions reveal their impacts on the optimal parameter allocations. Therefore, this application of the energy flow model shows its advantages for both performance analyses and system optimization.
  • Theoretical Leidenfrost point (LFP) model for sessile droplet
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Chang Cai, Issam Mudawar, Hong Liu, Chao Si In the present paper, a theoretical investigation is undertaken in pursuit of a new mechanistically based Leidenfrost point (LFP) model for a sessile droplet. The model consists of sub-models describing temporal variations of droplet size and shape, and thickness of the vapor layer separating the droplet from the heating surface during the evaporation process. Starting from the film boiling regime, it is shown that decreasing surface temperature causes monotonic thinning of the vapor layer. The primary hypothesis of the model is that as Leidenfrost temperature is reached, the vapor layer becomes sufficiently thin to enable surface roughness protrusions to breach the droplet underside. It is shown that, because of the stochastic nature of surface roughness, an appropriate statistical parameter of surface height must be determined for comparison with the vapor layer thickness. Using surface profiles measured by the authors along with those obtained from prior studies, it is shown how this statistical parameter may be related to other commonly available parameters. Overall, the model shows good accuracy in predicting temporal records of droplet size and shape, and vapor layer thickness for different liquids and surface temperatures. Combined with the statistical surface height parameter, the model shows very good accuracy in predicting the Leidenfrost temperature, evidenced by a mean absolute error of 7.77%.
  • Heat transfer in the hydraulic jump region of circular free-surface liquid
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Hossein Askarizadeh, Hossein Ahmadikia, Claas Ehrenpreis, Reinhold Kneer, Ahmadreza Pishevar, Wilko Rohlfs Because of its high heat transfer potential, liquid jet impingement is broadly used in cooling applications. As a free-surface jet spreads radially after impinging on a flat surface, a hydraulic jump can occur that severely affects the heat transfer. This study numerically scrutinizes the effects of different flow structures within the jump on the local heat transfer of the impinged plate subjected to a uniform heat flux. For the numerical simulations, a modified version of the interFoam solver of OpenFOAM is used, in which the interface compression scheme is amended implementing the continuum surface stress method. To create different flow structures in the jump region, an obstacle with a varying height is placed at the edge of the impinged plate. Jump structures and the transitions between them are distinguished by virtue of the appearance of a separation bubble on the bottom surface and/or a roller underneath the interface in the jump region. The results show that the hydraulic jump in itself reduces the local Nusselt number, whereas the roller underneath the free surface slightly improves the heat transfer. The minimum heat transfer rate occurs right before the separation bubble (at the separation point); however, the local stagnation point ahead of the separation bubble increases the Nusselt number.
  • Experimental investigation of surface temperature non-uniformity in spray
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Xiao Zhao, Zhichao Yin, Bo Zhang, Zhuqiang Yang The surface temperature non-uniformity is crucial in understanding the heat transfer mechanism of spray cooling. It is also a sensitive factor in the thermal management of electronic devices or in the application of transient sprays where the surface heat flux is obtained from the internal temperature measurement. In this study, the effects of heat flux, subcooling, nozzle-to-surface height, and injection pressures on the surface temperature uniformity in a spray cooling application were studied. The distribution of droplet diameter and the spray volumetric flux was found to significantly vary under the above experimental conditions. A higher spray volumetric flux and smaller droplet diameter resulted in a lower surface temperature. In general, the spray volumetric flux is the dominant parameter. The effect of droplet diameter distribution always became obvious with low spray volumetric flux. Regarding the high spray volumetric flux, there was an offset between these two parameters. The results also indicated that increasing the heat flux, nozzle-to-surface height, and subcooling, as well as decreasing the inlet pressure, all resulted in higher surface temperature uniformity owing to the variation in the droplet diameter and spray volumetric flux distributions. Finally, prediction methods for temperature non-uniformity were proposed for single-phase and two-phase regimes.
  • Microporosity formation and dendrite growth during solidification of
           aluminum alloys: Modeling and experiment
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Qingyu Zhang, Dongke Sun, Shiyan Pan, Mingfang Zhu A coupled lattice Boltzmann-cellular automaton-finite difference (LB-CA-FD) model is proposed for the simulations of hydrogen porosity formation during dendritic solidification of binary hypoeutectic aluminum alloys. The present model involves the effect of hydrogen and solute partitioning at the solid/liquid interface, and the transport of hydrogen and solute concentrations as gas bubbles and dendrites grow in two and three dimensions. The dendrite growth and solute transport are simulated using a CA-FDM approach. The nucleation, growth, and movement of gas bubbles, as well as the transport of hydrogen, are calculated using the multi-phase LB model. After model validation by the tests of Laplace’s law and contact angle simulations on smooth and rough solid surfaces, the proposed model is applied to simulate the temporal evolution of hydrogen porosities and their interaction with dendrites during solidification of an Al-4 wt% Cu alloy. The simulated morphologies of gas pores and dendrites compare reasonably well with the experimental micrograph reported in the literature. The simulation results show that the gas bubbles nucleate at the roots of secondary dendrite arms preferentially. The competitive growth between the bubbles is visualized and found to be coherently controlled by bubble size, hydrogen supersaturation, and local hydrogen concentration in liquid. The simulations of microporosity formation together with columnar dendrite growth during directional solidification of an Al-4 wt% Cu alloy are carried out in two and three dimensions. It is found that the bubbles could move in the interdendritic liquid channel in the two-dimensional case. In the three-dimensional simulation, however, the bubbles are probably pinned by the secondary arms and thereby remain stationary. The three-dimensional simulation results are identical with the in situ experimental observation.
  • Multi objective optimization of a micro-channel heat sink through genetic
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Yildizeli Alperen, Cadirci Sertac In this study, fluid flow and conjugate heat transfer in a micro-channel heat sink (MCHS) is simulated with ANSYS-Fluent and optimized with multi objective genetic algorithm known as elitist Non-Dominated Sorting Genetic Algorithm (NSGA-II) coded in MATLAB. Single phase, steady and fully developed liquid flow in the range of the inlet Reynolds number 500–1000 through a 3D micro-channel is solved by the laminar flow solver. The coolant fluid is considered as deionized water with dynamic viscosity depending on temperature. The geometric variables (channel width and height) of the micro-channel related to the channel’s cross section and the inlet Reynolds number related to the flow rate are selected as design variables for the optimization. Two normalized objective functions of the Nusselt number and pumping power are chosen to assess the hydrodynamic and thermal performances of the MCHS. The optimization is performed for 20 generations with a number of population of 30. Optimal Pareto Front representing the trade-off between the objective functions is obtained, which provides useful results for the design of MCHS. The final generation of the optimization process reveals that in most of the design variable sets, the design points are identified as uniform distribution for the inlet Reynolds number within the limits and 0.29 mm for the micro-channel’s width. However, the micro-channel’s height was suggested in the range of 0.50–0.67 mm in most optimum cases.
  • Three-dimensional Green’s functions for transient heat conduction
           problems in anisotropic bimaterial
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Jiakuan Zhou, Xueli Han In this paper, three-dimensional Green’s functions for transient heat conduction problems in general anisotropic bimaterial are obtained based on two-dimensional Fourier transform and Laplace transform, and are separated as a sum of a full-space Green’s function and a complementary part. We can get the bimaterial Green's functions in the transformed domain by boundary conditions, and then in the physical domain by the inverse Fourier and Laplace transform. Although the present paper aims to develop Green's function in anisotropic bimaterial, the derived solutions can be reduced to simple cases, such as in isotropic or orthotropic materials, and in half-space or full-space. Moreover, this method can be extended to derivation of new Green’s functions in multi-layer materials. Numerical examples are presented to verify the validity and applicability of present solutions. When the source is constant and time extends to infinity, the present transient solution approaches the steady one. Besides, the anisotropic solution indicates high correlation with the properties of material.
  • Experimental study on thermal performance of water-based nano-PCM emulsion
           flow in multichannel heat sinks with parallel and divergent rectangular
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): C.J. Ho, Shao-Teng Hsu, Jer-Huan Jang, Seyyede Fatemeh Hosseini, Wei-Mon Yan In this work, an experimental study is arranged to investigate the cooling efficacies of water-based nano-PCM emulsion flow in the multi-channel heat sinks with parallel and divergent rectangular mini-channels. N-eicosane particles with size of 130 nm are considered as the phase change material (PCM) nanoparticles. Two multi-channel heat sinks with eight parallel and divergent mini-channels are fabricated. The divergent channel has a divergent angle of 2.06°. The effects of different parameters including volumetric flow rate of working fluid (60 cm3/min < Q̇ < 600 cm3/min), heat flux (3.2 W/cm2 < qh′′ 
  • Efficient hybrid microjet liquid cooled heat sinks made of photopolymer
           resin: thermo-fluid characteristics and entropy generation analysis
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Luis E. Paniagua-Guerra, Bladimir Ramos-Alvarado In this contribution, an investigation on the performance of a hybrid design of active liquid cooled heat sinks is presented. A numerical analysis was performed via 3-D CFD simulations of a set of hybrid microjet heat sinks formed by a pair of fractal channel manifolds, used as liquid inlet and outlet conduits (manufactured in stereolithographic resin), an array of impinging microjets for uniform cooling, and a metallic heat spreader attached to a heat source. The pressure losses generated by the small channels in the manifolds were targeted for minimization using various structural modifications, while the metallic heat spreader in contact with the heat source was optimized for improving the cooling capabilities of the heat sink. A parametric analysis was conducted to determine the improvements in the overall performance; additionally, a local entropy generation analysis was conducted to obtain a heat sink design with the lowest intrinsic irreversibility. The entropy generation rates were obtained by coupling a local entropy generation model with the governing equations in the CFD simulations. The results obtained from the entropy generation analysis indicated that the major irreversibility source is the heat transfer in the metallic heat spreader. The addition of area-enhancement features, such as microchannels and pin fins to the original heat spreader led to increasing the cooling capabilities of the hybrid heat sinks. The implementation of the entropy generation analysis allowed to identify the local sources of irreversibility and the impact of the hydrodynamic and thermal deficiencies in the operation of the heat sink. Lastly, an overall performance indicator (PPTR) enabled a proper assessment of the thermo-fluid response of the heat sinks and the results drawn from this parameter matched the fundamental observations obtained from the entropy generation analysis.
  • Film-wise condensation of R-134a, R-1234ze(E) and R-1233zd(E) outside the
           finned tubes with different fin thickness
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Wen-Tao Ji, Xiao-Dong Lu, Qiu-Nan Yu, Chuang-Yao Zhao, Hu Zhang, Wen-Quan Tao Film-wise condensation of R-134a, R-1234ze(E) and R-1233zd(E) outside two enhanced tubes was experimentally investigated. The two tubes have the same fin density and similar fin height while the fin thickness is different. In the experiment, the saturation temperature was 36 °C. Heat flux was in the range of 20–90 kW·m−2. It was found that R-134a was more efficient than other refrigerants and gave the highest heat transfer performance outside the two tubes. R-1233zd(E) was the lowest. Condensing heat transfer coefficient of R-134a was approximately 2 times higher than R-1233zd(E). As heat flux was higher than 20 kW·m−2, condensing heat transfer coefficient of R-134a and R-1234ze(E) all decreased as the increasing of heat flux. While for R-1233zd(E), up to the heat flux of 90 kW/m2, the condensing heat transfer coefficient is ever-increasing as the increasing of heat flux. The condensing heat transfer of R-134a was 10–20% higher than R-1234ze(E). The trend of variations for the heat transfer performance of R-134a and R-1234ze(E) was similar. The present work examined the heat transfer characteristics of finned tubes with different fin thickness. It is helpful for the designers to summarize the heat transfer performance of some new HFOs refrigerants having the potential to be used in the water cooled chillers or heat pumps.
  • Heat transfer and melt dynamics of millimetric ice particles impacting a
           heated water bath
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Katherine Baskin, Katharine M. Flores, Patricia B. Weisensee In metallic additive manufacturing using direct energy deposition, particles and melt pool undergo complex interactions, including particle impact, penetration, and melting. The spatio-temporal evolution of these processes dictates the solidified material microstructure and final workpiece quality. However, due to the opaqueness of metallic melt pools, in-situ visualization is nearly impossible. To model this system, we use high-speed imaging to investigate the heat transfer and melting dynamics of spherical ice particles (D ≈ 2 mm) impacting heated water baths of varying temperatures (23–70 °C) with velocities ranging from 0.8 to 2.1 m/s. To visualize the outflow of molten ice, representative of mixing and material homogeneity, the particles were colored with food dye. We show that after impact, molten liquid forms an annular plume travelling downwards in the bath, until hitting the bottom of the enclosure and expanding radially. Due to positive buoyancy forces, unmolten ice particles rise to the top of the water bath, where they fully melt. As temperatures increase, we observe random particle movement, indicating the presence of convective currents. Through video analysis, we examine the relationships between bath temperature, impact velocity, and heat transfer. As expected, increasing the bath temperature decreases the total melt time of the ice particle. Interestingly, the impact velocity has only a minor effect on the melting time. Using non-dimensional analysis, we derive an expression for the correlation between Nusselt and Stefan numbers. Insights from this work can be used to match characteristic time scales during additive manufacturing to tailor material properties.
  • Macroscopic transport properties of Gyroid structures based on pore-scale
           studies: Permeability, diffusivity and thermal conductivity
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Ji-Wang Luo, Li Chen, Ting Min, Feng Shan, Qinjun Kang, WenQuan Tao Gyroid structure is a kind of triply periodic minimum surface, which presents several advantages such as free-standing, highly ordered and interconnected pore network and high specific surface area. Understanding transport processes inside the Gyroid structure is important for its application. In this study, porous structures of the Gyroid are reconstructed, and then pore-scale studies of fluid flow, diffusion and heat transfer in the two phases of Gyroid structures are numerically implemented using the lattice Boltzmann method (LBM). Pore-scale velocity, concentration and temperature fields inside the Gyroid structures are discussed, based on which macroscopic properties including permeability, effective diffusivity, effective thermal conductivity, and tortuosity are predicted. There are two phases in the Gyroid structures, and both phases are continuous, leading to the bicontinuous characteristic of Gyroid structures. The results show that transport resistance in one phase is lower than that in the other phase. Thus from the perspective of enhancing transport process, it is desirable to choose the phase with higher transport properties for transporting the slower process. The present study provides guidance for subsequent applications of Gyroid structure.
  • Influence of the dynamical free surface deformation on the stability of
           thermal convection in high-Prandtl-number liquid bridges
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Luis M. Carrión, Miguel A. Herrada, José M. Montanero We analyze theoretically the stability of the thermal convection in high-Prandtl-number liquid bridges. The steady axisymmetric base flow, as well as its corresponding linear non-axisymmetric eigenmodes, are calculated taking into account the free surface deformation caused by both that flow and the perturbations. The stability limits and the oscillation frequencies obtained from the linear stability analysis satisfactorily agree with previous experimental data. The dynamical free surface deformation produced by the base flow approximately coincides with that measured in the experiments. When the deformations are normalized with their corresponding values of the Capillary number, they collapse onto a single curve. The dependence of the free surface oscillation amplitude with respect to the axial coordinate approximately coincides with that measured in previous experiments. Our results show that the dynamical free surface deformation has very little effect on the eigenvalues characterizing the linear modes, and, therefore, on the stability limits.
  • Numerical investigation of tubular exhaust reformer with thermochemical
           recuperation for LNG engine
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Zunhua Zhang, Renmin Wu, Shangsheng Feng, Yanxiang Long, Gesheng Li A three-dimensional tubular exhaust reformer was investigated to study the effects of EGR ratio and the amount of the steam addition on the methane-exhaust gas reforming process under different excess air coefficients. The objective was to maximize hydrogen production economically, by regulating the amount of exhaust gas and the steam addition at the inlet of the reaction tube with the amount of methane addition fixed. Coupled with the detailed catalytic reaction mechanism based on Rh-Al2O3 catalyzer, the exhaust gas reforming process in a fixed bed reactor was simulated by using a porous media model. The results showed that, in the entry region of the reaction zone, oxidation reaction dominates with significant heat release; whilst after the entry region steam reforming reaction dominates with heat absorbing. The exhaust gas outside the reaction tube played the role of preheating the mixture before the reaction zone and heat preservation in the reaction zone. Results showed that with the methane addition fixed, there is an optimum M/O value (about 2) and W/M value (about 1.25) for maximum hydrogen production. In addition, the surface coverage ratio of coke deposit in the reaction bed decreases with the increase of EGR ratio and steam addition.
  • Frost growth behavior according to the cold surface inclination angle
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Junghan Kim, Sungjoon Byun, Jaehwan Lee, Kwan-Soo Lee Frosting experiments were performed to analyze the frost growth behavior according to the inclination angle of a cold surface. The thickness and density of frost on an inclined cold surface were analyzed with respect to a horizontal cold surface. The scattering of the frost particles and the initial shape of the frost crystals were observed. The frost thickness increased and the frost density decreased as the cold surface inclination angle increased, even with variable operating conditions (humidity and cold surface temperature). In the case of varying humidity, the initial frost crystals exhibited feather shapes under relatively high humidity conditions, and needle and pole shapes under relatively low humidity conditions. The decrease in frost density owing to frost particle scattering was significant when feather-shaped crystals were observed. As the cold surface temperature increased, the frost layer was strongly bound, and frost particle scattering occurred less frequently.
  • Measurement of the microlayer characteristics in the whole range of
           nucleate boiling for water by laser interferometry
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Zhihao Chen, Xiaocheng Hu, Kang Hu, Yoshio Utaka, Shoji Mori During nucleate boiling, a thin liquid film (microlayer) is formed beneath a boiling bubble when the bubble undergoes rapid growth/expansion. The linear distribution of the microlayer has been previously confirmed, and its crest shape has been observed in the isolated bubble region of nucleate boiling. However, the microlayer behavior in larger heat flux regions up to critical heat flux has not yet been elucidated. In this study, to further understand the microlayer structure in the whole heat flux range of nucleate boiling, microlayer configuration was measured using laser interferometry. Water was adopted as the test fluid, and it is confirmed that the microlayer can be observed over a whole range of nucleate boiling containing the critical heat flux point. It is also confirmed that the deformation of the microlayer from axisymmetric shape was caused by complicated, irregular bubble motions such as bubble coalescence, which was observed for relatively higher heat flux. The crest shape of the microlayer, which appears near the periphery of its maximum diameter under relatively smaller heat flux, was not observed at a relatively higher heat flux. Finally, it is confirmed that heat flux does not obviously influence the thickness distribution of the initial microlayer.
  • Constructal design of subcooled microchannel heat exchangers
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): David O. Ariyo, Tunde Bello-Ochende This paper presents geometric optimization and flow parameters modelling for subcooled flow boiling (two-phase flow). The objective of the paper was to minimize the thermal resistance of the microchannel heat exchanger subject to fixed volume constraints of heat sink and microchannel. The geometric and flow parameters were allowed to morph, according to the constructal design principles to obtain their optimized values. The flow was highly subcooled at inlet temperature of 25 °C using deionized water as the cooling fluid and aluminium as the heat sink material. Velocities between 0.1 and 4.5 m/s and heat fluxes between 100 and 1200 W/cm2 (1 × 106 W/m2 and 1.2 × 107 W/m2) were used in the modelling and optimization. Computational fluid dynamics code, ANSYS was used for both the simulations and the optimization of the configurations. The numerical code used for the simulations was validated by available experimental data in the literature and the agreement showed the capability of CFD (ANSYS) to predict accurately, subcooled flow boiling (two-phase flow) in rectangular microchannel heat exchangers for cooling of microelectronic devices. Comparisons were made between two-phase flow and single-phase flow by using their optimized geometric and flow parameters, and the results clearly demonstrated the superiority of two-phase flow regime in rectangular microchannels for removal of high heat fluxes at low Reynolds numbers. As the optimized Reynolds number increases, the minimized thermal resistance (peak temperature) decreases which is consistent with previous results obtained in the open literature. Results further show the aspect ratio, the optimized diameter and axial length of the microchannel as a function of the dimensionless pressure drop number (Bejan number).
  • LBM modelling of supercooled water freezing with inclusion of the
           recalescence stage
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Shaolei Gai, Zhengbiao Peng, Behdad Moghtaderi, Jianglong Yu, Elham Doroodchi Once nucleated, the solidification process of supercooled water undergoes stages of recalescence, freezing, and solid cooling. In existing LBM models for predicting the water solidification process, the recalescence stage was often treated by simply setting the system temperature to 0 °C on account of the latent heat release. However, apart from the temperature rise, another important feature of the recalescence stage is the rapid growth of dendritic ice over the entire supercooled space, which was often overlooked. In this study the recalescence stage is included in the conventional LBM, aiming to quantify the effect of initial ice fraction distribution on the freezing kinetics of supercooled water.Good agreements are achieved between the predicted results and the experimental data on the kinetics of water freezing in terms of the local temperature variation, freezing rate and evolution of the ice-water interface. However, the conventional LBM without considering the recalescence stage provides a poor description of ice-water interface evolution. The discrepancy between the predicted results using models with and without considering the recalescence stage increases as the supercooling increases and rises to 31% for a supercooling of 20 °C. Moreover, the method based on the Stefan number proves valid in calculating the initial ice fraction over the entire spectrum of supercooling degrees, whereas for high supercooling degrees (>28.2 °C) the application of the enthalpy-based method leads to erroneous results. For water systems of small volume that often bear a supercooling more than 30 °C, the recalescence stage should be considered in the modelling.Graphical abstractGraphical abstract for this article
  • Refrigerant condensation in vertical pipe minichannels under various heat
           flux density level
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Tadeusz Bohdal, Marcin Kruzel This work is a study of the condensation process taking place in the conditions so far unproven. It was devoted to selected problems accompanying the condensation phenomenon occurring in a mini scale. The work is a continuation and development of the authors' research to-date. Paper describes the flow condensation of high-pressure refrigerants through channels made of stainless steel AISI 304 and AISI 316L with various inner diameter di. A new heat transfer universal correlation was developed on the basis of own experimental data for high pressure refrigerants condensation in pipe minichannels.
  • Heat transfer enhancement, entropy generation and temperature uniformity
           analyses of shark-skin bionic modified microchannel heat sink
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Ping Li, Dingzhang Guo, Xinyue Huang Inspired by the shark-skin bionic concept, four novel flow control devices are proposed in this study to further enhance thermal performance (TP) with low entropy generation (S/S0), as well as to improve temperature uniformity. Then, the flow structures and heat transfer characteristics of water-cooled microchannel heat sink (MCHS) modified by the proposed devices (Model A, Model B, Model C and Model D) are investigated in laminar flow regime (Re = 50–700). Results show that the variation trends of TP for different MCHS increase as Re increases, and the TP of all cases ranges from 1.1 to 3.1. And, the S/S0 of all MCHS maintain low at small Re, which increases quickly as Re further increases. When Re is small (Re = 50–250), the largest TP is obtained by Model B with the smallest S/S0. As Re is larger than 500, the TP and S/S0 of Model D both become the largest. The varied geometry of flow control devices pushes main flow towards to side walls, and the sequential contraction and expansion area of split passage enhance the fluid exchange. However, the secondary flow generated by flow control device is not intense enough to cool down side walls when Re is small. Therefore, the temperature uniformity of MCHS is improved significantly with the increase of Re. The temperature uniformity of Model D is inferior to that of Model C due to hot spots exist at the narrow split passage. Furthermore, at large Re, Model C is superior to others, because the significant improvement of TP is achieved herein with acceptable S/S0.
  • An evaluation of vaporization models for a cryogenic liquid spreading on a
           solid ground
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Le-Duy Nguyen, Myungbae Kim, Byungil Choi, Kyungyul Chung, Kyuhyung Do, Taehoon Kim The spreading and vaporization of a hazardous cryogenic liquid due to its accidental release on solid ground may result in a pool fire, an explosion, or a hazardous vapor cloud. Many mathematical models have been built to predict the spreading and vaporization of a liquid pool. To determine the heat flux from the ground to the liquid pool two boundary conditions (BCs) at the ground surface have been commonly used: (i) specified heat flux and (ii) specified temperature. The first BC is derived from predictive correlations for boiling heat transfer regimes (BR-BC) that are dependent on the temperature difference between the liquid and the ground surface, while the second is based on an assumption of perfect thermal contact (PTC-BC) between the liquid and the ground. However, the influence of the selection of these BCs on the model predictions still needs to be investigated. To this end, we implemented both types of BCs in liquid spreading models and then compared the results. In addition, experiments were conducted for liquid nitrogen (LN2) and liquid oxygen (LOX) to observe pool spreading and pool regression. The PTC-BC was in better agreement with the experimental results than the BR-BC. At the initial stage, the BR-BC underestimated the vaporization velocity and over-predicted the pool radius because the boiling regime correlations did not account for the effects of the radial flow. The two BCs agreed well at the later stages. It is recommended that the PTC-BC should be used for a spreading pool while the BR-BC should be used for a non-spreading pool.
  • Measurement of transient evaporation of an ethanol droplet stream with
           phase rainbow refractometry and high-speed microscopic shadowgraphy
    • Abstract: Publication date: January 2020Source: International Journal of Heat and Mass Transfer, Volume 146Author(s): Can Li, Qimeng Lv, Yingchun Wu, Xuecheng Wu, Cameron Tropea Quantifying the evaporation rate of droplets is of great importance in many applications and this is especially true if the evaporation occurs in a rapidly changing environment, such that models describing evaporation under steady state conditions are no longer valid. To achieve such information from experiments, the phase rainbow refractometry (PRR) technique has recently be shown to be capable of simultaneously measuring temperature, size, and size variation at the nanometer scale, quantities essential for quantifying transient evaporation rates. The present study examines the use of the PRR technique to characterize the evaporation of monodispersed droplets in a droplet stream injected into ambient air. This is combined with high-speed microscopic shadowgraphy, yielding as measured quantities droplet diameter, diameter change, temperature evolution, velocity and computed transient evaporation rate of the droplet stream. The accuracy and resolution of the measurements are evaluated by comparison with theoretical values and values measured with alternative means. Furthermore, the results are used to investigate how the evaporation rate is modified by interaction among droplets in the droplet stream and how these rates differ from evaporation rates predicted for isolated droplets, using the well proven Abramzon and Sirignano model. Finally, the evaporation rate, including the influence of droplet interaction, is shown to be in line with correlations suggested by Virepinte; refinement to this correlation is proposed.
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