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International Journal of Heat and Mass Transfer
Journal Prestige (SJR): 1.498
Citation Impact (citeScore): 4
Number of Followers: 261  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0017-9310 - ISSN (Online) 0017-9310
Published by Elsevier Homepage  [3162 journals]
  • A thermal non-equilibrium approach on thermo-solutal natural convection
           due to the lateral flux of heat and solute on enclosure walls:
           Multi-solutions and oscillations
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): P. Bera, Sarita Pippal, Arshan Khan In this paper, we address the influence of the thermal non-equilibrium state on double-diffusive convection in a porous enclosure, subject to constant heat and solute fluxes at the vertical walls, while other walls of the enclosure are adiabatic. For this, Darcy model has been adopted. The governing equations are solved numerically by the ADI method and analytically by using parallel flow assumption valid for the slender enclosure. A comparative study has been made in between buoyancy aiding flow(i.e., buoyancy ratio, N>0) and buoyancy opposed flow(i.e., buoyancy ratio, N
       
  • Dropwise condensation on superhydrophobic nanostructure surface, Part I:
           Long-term operation and nanostructure failure
    • Abstract: Publication date: February 2019Source: International Journal of Heat and Mass Transfer, Volume 129Author(s): Jian Xie, Jinliang Xu, Xiang Li, Huan Liu Dropwise condensation heat transfer (DWC) on superhydrophobic nanograsses surface (NGS) was investigated for long-term operation. For DWC of pure water-vapor on fresh NGS, two heat transfer regimes are identified: higher heat transfer coefficients with droplet jumping, and constant heat transfer coefficients with droplet rolling. The one-week operation not only deteriorates heat transfer performance, but also changes jumping or rolling mode to sliding mode. The condensation heat transfer coefficients are apparently decreased from first to third day, but they approach a limit value since the third day. In order to identify if the single-molecule-layer of polymer (SML) modified on nanograsses was destroyed, DWC on a smooth single-molecule-layer of polymer surface (SSML) was tested to display stable heat transfer with drop sliding for one-week operation, concluding no failure of the polymer layer. The collapse and breakage of nanograsses were observed to explain the decayed heat transfer versus time on NGS. Compared with SSML, the NGS has smaller droplet departure size but lower heat transfer coefficients, indicating positive and negative effects after introducing nanostructures. Three nanostructure failure mechanisms are proposed. This work suggests a new research field of the nanoscale fluid-wall interaction.
       
  • Experimental investigation on the effects of rotation and the blowing
           ratio on the leading-edge film cooling of a twist turbine blade
    • Abstract: Publication date: February 2019Source: International Journal of Heat and Mass Transfer, Volume 129Author(s): Hai-wang Li, Feng Han, Yi-wen Ma, Hai-chao Wang, Zhi-yu Zhou, Zhi Tao An experimental investigation has been performed to investigate the effects of the rotation and blowing ratio on the film cooling effectiveness distributions of the leading-edge regions of a twist gas turbine blade using a thermochromic liquid crystal (TLC) technique. The experiments were carried out at three rotating speeds, including 400 rpm (positive incidence angle), 550 rpm (zero incidence angle), and 700 rpm (negative incidence angle). The averaged blowing ratio ranged from 0.5 to 2.0. CO2 was used as the coolant to ensure that the coolant-to-mainstream ratio was equal to 1.56. The Reynolds number, based on the mainstream velocity of the turbine outlet and the rotor blade chord length, was 6.08 × 104. The effects of the rotating speed and the blowing ratio were analyzed based on the film cooling effectiveness distribution. The results show that rotating speed plays an indispensable role in determining the film cooling effectiveness of distributions on the leading edge. The position of the stagnation line moves from the pressure side (PS) to the suction side (SS) via an increase in rotating speed. Under the same blowing ratio, the area-averaged film cooling effectiveness increases monotonously with an increase in rotating speed. Under the same rotating speed, the area-averaged film cooling effectiveness increases with the increase in blowing ratio. More details about the effects of the rotation speed and blowing ratio on the spanwise averaged film cooling effectiveness of the leading-edge region are shown in this study.
       
  • The coordination distribution analysis on the series schemes of heat
           exchanger system
    • Abstract: Publication date: February 2019Source: International Journal of Heat and Mass Transfer, Volume 129Author(s): Jiangfeng Guo, Xinying Cui, Xiulan Huai, Keyong Cheng, Haiyan Zhang The influences of series schemes on the heat exchanger system are investigated using matrix analysis method in the present work. The performance of heat exchanger system can be improved by arranging the series schemes without an obvious increase of pressure drop or heat transfer area. The matrix analysis indicates that the series scheme has important effect on the parameter distribution over the heat exchanger system. The heat transfer can be enhanced by improving the distributed coordination between heat transfer coefficient and temperature difference besides increasing their values. The better distributed coordination between heat transfer coefficient and temperature difference corresponds to the better uniformity of heat transfer rate over the heat exchanger system, which is favorable to safety running of system. The matching performance improvement between the entransies of hot and cold fluids could lead to the better distributed uniformity of entransy dissipation over the heat exchanger system, which results in the reduction of the total entransy dissipation finally. The present work might provide a new approach to the optimization and layout of heat exchanger system for the fluids with drastic changes of properties.
       
  • A generalized thermal conductivity model for nanoparticle packed bed
           considering particle deformation
    • Abstract: Publication date: February 2019Source: International Journal of Heat and Mass Transfer, Volume 129Author(s): Lin Zizhen, Huang Congliang, Li Yinshi Theoretically understanding the thermal conductivity of the nanoparticle packed beds (NPBs) is critical for designing high-performance thermal insulation materials. Currently, the classical effective medium assumption (EMA) model, Nan model, just show their good prediction at a high porosity of NPBs (≥0.75). Herein, we propose a generalized model of the thermal conductivity that almost covers the whole porosity range by considering the effect of the nanoparticle deformations on the thermal contact resistance (R). It has been demonstrated that our model matches the experimental results great well. It is also found that at high porosity R is dominated by the phonon diffusive scatterings (Rcd), while it is determined by the phonon ballistic scatterings (Rcb) at a low porosity. More interestingly, R can determine the porosity at which the lowest thermal conductivity of NPBs appears. This work opens a new way to design the desired thermal insulation materials.
       
  • Characterization of transport limitations in SAPO-34 adsorbent coatings
           for adsorption heat pumps
    • Abstract: Publication date: February 2019Source: International Journal of Heat and Mass Transfer, Volume 129Author(s): Jens Ammann, Bruno Michel, Patrick W. Ruch Adsorption heat pumps have become an increasingly viable technology to use waste heat or renewable thermal energy for heating and cooling. The power density of this emerging technology is limited by the rate of heat and/or mass transfer in the adsorption heat exchanger (AdHEX) which drives investment costs. This work presents an experimental analysis of the mass and heat transfer during water sorption on SAPO-34 coatings to determine the limiting transport mechanism in state-of-the-art AdHEX. Isochoric temperature swings were carried out and evaluated using a recently introduced method to determine the relative importance of heat and mass transport impedances. Coatings with thicknesses between 60 and 460 µm were investigated and in all cases the sorption dynamics were limited by mass transport. Ragone plots were used to characterize the power and energy trade-off during thermal cycling of SAPO-34 in water vapor to identify the pareto-optimal cycle time for a specific coating thickness. With the knowledge of the rate-limiting mechanism, the overall transport rates of adsorbent coatings can systematically be improved to enhance transport rates in next-generation AdHEX.
       
  • Modeling heat capacity of ionic liquids using group method of data
           handling: A hybrid and structure-based approach
    • Abstract: Publication date: February 2019Source: International Journal of Heat and Mass Transfer, Volume 129Author(s): Alireza Rostami, Abdolhossein Hemmati-Sarapardeh, Abdorreza Karkevandi-Talkhooncheh, Maen M. Husein, Shahaboddin Shamshirband, Timon Rabczuk Ionic liquids (ILs) are a significant class of chemicals with applications in solar cells, sensors, capacitors, batteries, plasticizers and thermal fluids. These compounds have attracted wide attention due to their low vapor pressure, tunable viscosity, non-flammability, wide liquid region phase diagrams and substantial chemical and thermal stability. Moreover, ILs structures can be easily modified leading to highly tunable physicochemical properties, which widen the application of these compounds. Heat capacity of ILs is an essential property for heat transfer evaluation as well as the estimation of widely used thermodynamic properties. Establishing a generalized and accurate model for predicting the heat capacity of ILs is valuable for their further development. In this manuscript, a hybrid group method of data handling (GMDH) was employed to establish a model estimating the ILs heat capacities. The database employed is an all-inclusive source of data taken from NIST standard, which includes the heat capacities of 56 ILs as a function of temperature and four structural parameters. About 80% of the database was assigned for building the model, and the remainder was used for evaluating the model performance. Statistical parameters and graphical techniques revealed that the model developed in this study is very accurate, with an R2 value of 0.982 and an average absolute percent relative error (AAPRE) of 1.84%. Moreover, the sensitivity analysis showed that the chemical structure of the cation has the highest impact on the heat capacity of ILs.
       
  • Turbulent molten pool analysis of tandem GMA automotive steel sheet
           welding
    • Abstract: Publication date: February 2019Source: International Journal of Heat and Mass Transfer, Volume 129Author(s): Kyungbae Park, Hunchul Jeong, Sungjin Baek, Dong-Yoon Kim, Moon-Jin Kang, Jungho Cho In this research, a three-dimensional turbulent weld pool simulation technique of tandem gas tungsten arc welding (GMAW) in a lap joint fillet is described and compared to a conventional laminar flow simulation. Basically, four governing equations are adopted for continuity, namely, continuity, Navier-Stokes, energy, and the popular volume of fluid equations. According to the basic theory of an arc weld pool, all known characteristics such as the arc heat input, arc pressure, electromagnetic force, and Marangoni flow are applied to the analysis model as a body force term or boundary conditions. A conventional arc weld pool analysis usually adopts a laminar flow; however, its results have shown a weld bead shape that is quite different from an experiment of a tandem GMA lap joint fillet welding of an automotive steel sheet. Therefore, the authors suggest the use of a k-εturbulent analysis model and show that its results coincide with the experiment results.
       
  • Novel designs of charring composites based on pore structure control and
           evaluation of their thermal protection performance
    • Abstract: Publication date: February 2019Source: International Journal of Heat and Mass Transfer, Volume 129Author(s): Weijie Li, Jun Liang, Jingran Ge To improve the thermal protection performance of the charring composites in reentry vehicles subjected to the challenged aerothemodynamic environment, we design six kinds of charring ablators based on the pore structure control. At the same time, a thermal-fluid-chemical coupled ablation model is developed for evaluating the designed ablators’ performances. Based on this model, the coupled thermal-fluid-chemical responses of an existing composite with homogeneous pores’ distribution are calculated to validate the developed model. After that, the numerical results of the pore structure controlled charring composites indicate that a charring ablator with a reasonable pores’ distribution will have better thermal protection performance, especially in which the initial pores’ content rise at the locations near the ablator’s bondline and in the middle of the thickness. This study will be a guidance for the design of charring composites for thermal protection application in reentry vehicles in a quantitative and efficient manner.
       
  • Thin reaction zones in highly turbulent medium
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): V.A. Sabelnikov, R. Yu, A.N. Lipatnikov A big database (23 cases characterized by Damköhler number less than unity) created recently in 3D Direct Numerical Simulation (DNS) of propagation of a statistically one-dimensional and planar, dynamically passive reaction wave in statistically stationary, homogeneous, isotropic turbulence is analyzed. On the one hand, the DNS data well support the classical Damköhler expression, i.e., square-root dependence of a ratio of turbulent and laminar consumption velocities on the turbulent Reynolds number. On the other hand, contrary to the common interpretation of the Damköhler theory and, in particular, to the concept of distributed burning, the DNS data show that the reaction is still localized to thin zones even at Da as low as 0.01, with the aforementioned ratio of the consumption velocities being mainly controlled by the reaction-zone-surface area. To reconcile these apparently inconsistent numerical findings, an alternative regime of propagation of reaction waves in a highly turbulent medium is analyzed, i.e., propagation of an infinitely thin reaction sheet is theoretically studied, with molecular mixing of the reactant and product being allowed in wide layers. In this limiting case, an increase in the consumption velocity by turbulence is solely controlled by an increase in the reaction-sheet area. Based on physical reasoning and estimates, the area is hypothesized to be close to the mean area of an inert iso-scalar surface at the same turbulent Reynolds number. This hypothesis leads to the aforementioned square-root dependence. Thus, both the DNS data and the developed theory show that a widely accepted hypothesis on penetration of small-scale turbulent eddies into reaction zones is not necessary to obtain the classical Damköhler scaling for turbulent consumption velocity.
       
  • Advective-diffusive-reactive solute transport due to non-Newtonian fluid
           flows in a fracture surrounded by a tight porous medium
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Morteza Dejam A mathematical model is presented for advective-diffusive-reactive solute transport due to non-Newtonian fluid flows in a fracture surrounded by a tight porous medium. The interaction between the two media is handled by the continuity of solute concentration and diffusive flux at the interface. The semi-analytical solutions and their asymptotic behaviours are derived for concentration inside the tight porous medium, average concentration within the fracture, and average diffusive flux through the interface. The developed model is verified using a numerical simulation of the original governing equations and then it is compared with the existing theoretical models for solute transport in a fracture with porous walls. It is revealed that the Damköhler number in the finite fracture affects the breakthrough of the solute much more considerably compared to that in the matrix. However, the larger the rate of reaction in the fracture the slower the breakthrough of the solute. Also, the shear-thinning fluids lead to faster breakthrough of the solute than the Newtonian fluid and the shear-thickening fluids yield slower breakthrough of the solute respect to the Newtonian fluid. Moreover, the average diffusive flux through interface generally increases as the advection coefficient becomes larger. In addition, the Damköhler number in the fracture influences the average diffusive flux through interface more noticeably compared to that in the matrix. Nevertheless, the higher the rate of reaction in the fracture the lower the average diffusive flux through interface. Finally, the breakthrough of the solute occurs faster within the infinite fracture respect to the finite fracture.Graphical abstractSketch of a physical system (comprised of a fracture surrounded by a tight porous medium) where the advective-diffusive-reactive solute transport due to non-Newtonian fluid flows occurs.Graphical abstract for this article
       
  • Modeling Leidenfrost drops over heated liquid substrates
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Long Qiao, Zhong Zeng, Haiqiong Xie, Hao Liu, Liangqi Zhang To simulate Leidenfrost drops over a heated liquid pool (namely the liquid-substrate-based (LSB) Leidenfrost drops), a model of evaporation phase change contained within a three-fluid system is developed based on the ternary Cahn-Hilliard equations. In the numerical simulation, an axisymmetric model employing a hybrid LB-FD (lattice Boltzmann-finite difference) method is established, and the model and code are validated by two classical problems, i.e. lens spreading and drop evaporation. Then, the dynamics of LSB Leidenfrost droplets is unveiled numerically, and the results firstly present the distribution of evaporation flux, temperature and velocity near the LSB Leidenfrost drop. Meanwhile, this study also addresses the influence of several important parameters (including vapor Stefan number, vapor Prandtl number, drop Bond number, drop Ohnesorge number, releasing height and pool depth) on the evolution of drop volume and the configuration of quasi-equilibrium Leidenfrost system.
       
  • Analytical solutions of fluid flow and heat transfer in a partial porous
           channel with stress jump and continuity interface conditions using LTNE
           model
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Qi Li, Pengfei Hu Forced convection heat transfer is analytically performed in a channel partially filled with porous media located at two inner walls under local thermal non-equilibrium (LTNE) condition. A constant heat flux is imposed at the channel walls. The Brinkman extended Darcy model is applied in the porous region and the stress jump and continuity conditions are employed at the interface. Exact solutions are obtained for velocity, pressure drop, the fluid and solid temperatures and Nusselt number. The effects of pertinent parameters on the fluid flow and heat transfer are conducted. Furthermore, the solution for the Nusselt number is compared to that by applying the local thermal equilibrium (LTE) assumption and the validity of the LTE is examined. It is shown that by applying LTNE model for different solid to fluid effective thermal conductivity ratios (K) and Biot numbers (Bi), the variations of Nusselt number with hollow ratio include three types of curves, which are: a maximized Nusselt number occurs at a small optimum hollow ratio, Nusselt number monotonically decreases by increasing hollow ratio and a minimized Nusselt number occurs at a small hollow ratio, respectively. For high K, a small critical value of S at which the Nusselt number reaches to LTE Nusselt number occurs and it lowers with the increase of Bi number and the decrease of Darcy number; while for low K, the LTNE Nu number versus hollow ratio is almost the same with LTE Nu number and therefore the LTE is valid. The stress jump at the interface is found to have negligible effect on the Nusselt number and the pressure drop, except in a high Darcy number with a low stress jump coefficient where the calculation of pressure drop need to account for the stress jump effect at the interface and the Nusselt numbers for both LTE and LTNE models slightly differs from the case of stress continuity interface condition.
       
  • Contact line dynamics of two-dimensional evaporating drops on heated
           surfaces with temperature-dependent wettabilities
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Xuemin Ye, Xiangshan Zhang, Minglan Li, Chunxi Li, Shuai Dong The dynamics of the evaporation of a sessile drop on a uniformly heated, horizontal, solid substrate is considered. Based on the lubrication theory and Navier slip condition, an evolution equation for the drop height of the two-dimensional drop is established. The effects of evaporation and the dependence of liquid–solid, solid–gas, and liquid–gas surface tensions on temperature are analysed. The present model indicates that the drop evolution is governed by capillary force, gravity, thermocapillary force, and evaporation. Numerical results show that gravity exerts a promoting effect on drop spreading, while capillary force and thermocapillary force inhibit drop spreading. The typical features, including contact line pinning, partial pinning, and depinning modes during drop evaporation, are illustrated by changing temperature sensitivity coefficients in the present model. The contact line motion is controlled by the wettability of the substrate and the temperature sensitivity coefficient of the solid–gas interface has a great influence on contact line dynamics. It is effective to manipulate the contact line during the volatile drop movement by regulating the temperature sensitivity coefficient of the solid–gas interface theoretically. However, the realisation of manipulation is highly dependent on the development of measurement techniques.
       
  • A finite particle method with particle shifting technique for modeling
           particulate flows with thermal convection
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Z.L. Zhang, K. Walayat, C. Huang, J.Z. Chang, M.B. Liu Particulate flows with thermal convection are very challenging to simulate numerically due to the existence of constantly moving boundaries and complex heat-fluid coupling effects. Meshfree and particle methods have special advantages in modeling complex fluid flows with moving boundaries. However, previous works based on meshfree modeling mainly focused on either particulate flows only with momentum exchange or natural thermal convection. In this paper, a finite particle method integrated with particle shifting technique (FPM-PST) is developed for modeling particulate flows with thermal convection. FPM is an improved smoothed particle hydrodynamics (SPH) method with better accuracy while extremely irregular particle distribution may lead to ill-conditioned corrective matrix and terminate the simulation. PST can achieve regular particle distribution through shifting highly disordered particles while current PST is based on conventional SPH of poor accuracy. A number of numerical examples demonstrated that FPM-PST is a novel approach for modeling thermal particulate flows with good performance in accuracy and stability. It has better accuracy than the conventional SPH and can obtain comparable results with those from other sources. The unphysical voids can also be avoided by FPM-PST. From the FPM-PST simulations, it is observed that at relatively low Reynolds numbers thermal convection between hotter or colder particles and the fluid causes significant increase or decrease in the drag force acting on particles, while the thermal convection has little influence on the particle motion at relatively high Reynolds numbers.
       
  • Cell transport and suspension in high conductivity electrothermal flow
           with negative dielectrophoresis by immersed boundary-lattice Boltzmann
           method
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Qinlong Ren, Fanlong Meng, Cho Lik Chan The cell transport and suspension using AC electrokinetics is essential for cell patterning and other biomedical applications in microfluidics. To avoid the undue cellular stress and irreversible damage to cells caused by low conductivity media, direct manipulations of cells in physiological solution of high electrical conductivity without dilution becomes significant. The driving mechanism of alternating current electrothermal (ACET) flow makes it attractive for pumping the physiological conductivity solution and transporting cells through the electrohydrodynamic (EHD) force. In addition, negative dielectrophoresis (nDEP) force is induced on a cell when its electrical conductivity is lower than that of solution media. In this paper, the effectiveness of ACET flow and negative DEP force in high conductivity solution is novelly used simultaneously to achieve a successful long-range cell transport and suspension in the microfluidic chamber. An immersed boundary-lattice Boltzmann method (IB-LBM) is developed to investigate the cell transport and suspension mechanism with respect to AC voltage magnitude, electrical conductivities of cell and solution, cell initial position, and cell size. It is found that a sufficient DEP force is indispensable for stabilizing the cell transport process and anchoring cells by overcoming the cell-cell interaction. Based on this, the design of a lab-on-a-chip device to generate a large DEP force is essential for future research to realize an efficient AC electrokinetic-based cell transport and suspension in physiological fluids.
       
  • Numerical simulation of enhancing shale gas recovery using electrical
           resistance heating method
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Yudou Wang, Bo Liao, Li Qiu, Diansheng Wang, Qingzhong Xue Gas production from shale gas reservoirs can be enhanced by increasing the temperature of the reservoirs due to the increased desorption of the adsorbed gas. However, limited techniques are currently available for practically introducing heat into such low permeability reservoirs. This paper investigates the feasibility of an electrical resistance heating method to promote shale gas production by increasing the temperature of the reservoirs. To achieve our research goal, a mechanistic numerical model is developed to describe electrical field, temperature field, and pressure field. To capture gas flow in a shale gas reservoir, non-linear flow, diffusion and adsorption/desorption which are all dependent on temperature are incorporated into a dual continuum media model. In our study, the gas production enhancement by electrical heating with two parallel horizontal electrode wells is evaluated using this model. We then assess impacts of the thermal properties of the formation, electrode length, electrical power, Langmuir volume and starting time of heating on gas production. The results indicate that the electrical heating method using two parallel horizontal electrodes can be an efficient method to enhance shale gas production. The heat capacity and conductivity of the formation have significant impacts on gas production. Reservoirs with low conductivity and low heat capacity tend to produce more gas due to heating. Meanwhile, shale gas reservoirs with high Langmuir volume also tend to yield more gas due to heating for. To maximize gas production, electrical power should be optimized based on the properties of shale gas reservoir and heating equipment. Longer electrodes heat more formations of the reservoir and thus lead to higher gas production by using the electrical heating method. In order to efficiently enhance shale gas production, electrical heating should start later in gas production, instead of earlier.
       
  • Experimental investigation on the Leidenfrost phenomenon of droplet impact
           on heated silicon carbide surfaces
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): ZeFeng Wang, Jinbiao Xiong, Weiyi Yao, Wenhai Qu, Yanhua Yang Due to its superiority in suppressing hydrogen generation under severe accident conditions, silicon carbide (SiC) has been regarded as one of the promising candidates among the diverse accident tolerant fuel (ATF) claddings. Droplet impact experiments are conducted on preheated CVD-SiC surfaces with different roughness and the polished sintered-SiC and stainless-steel surface. The effects of surface roughness, contact angle and thermal properties on the impact behavior and cooling efficiency are discussed. The experiments are carried out in the range of 10 
       
  • Impact of an oscillating guide vane on the thermo-hydraulic fields in a
           square cavity with single inlet and outlet ports
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Yang-Cheng Shih, J.M. Khodadadi, Shih-Wei Nien, Yi Zeng, Xuan-Long Huang This study reports on a numerical investigation of the impact of an oscillating rigid plate guide vane on the transient behavior of thermo-hydraulic fields within a square cavity with single inlet and outlet ports. The computational fluid dynamics software ANSYS® FLUENT was employed to perform the numerical simulations. The numerical analysis focused on the effect of the frequency and amplitude of an oscillating rigid guide vane on modification of the transverse throughflow, internal flow re-distribution, re-arrangement of multiple rotating vortices and the ensuing heat transfer performance. According to the numerical results, it is shown that for a combination of the Strouhal number and amplitude of inclination angle of the guide vane, the instantaneous Nusselt number that is a measure of the thermal performance of the system exhibits cyclical changes once the respective periodic state was reached. Moreover, the cycle-averaged and peak-to-peak Nusselt number increases with the increase of the amplitude of oscillations as the frequency of oscillation is fixed. For a fixed amplitude of oscillation, the cycle-averaged and peak-to-peak Nusselt number decreases as the frequency increases. Instantaneous variations of the dimensionless pressure drop of the cavity also exhibited periodic oscillations. Enhancement of heat transfer due to oscillations of the guide vane was accompanied with the expense of increasing the pressure drop.
       
  • Nucleate boiling heat transfer model based on fractal distribution of
           bubble sizes
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Baojin Qi, Ya Wang, Jinjia Wei, Yonghai Zhang, Ting Yu Scientifically and accurately predicting the distribution of the bubble sizes on the heating surface is a key step to improve the calculation accuracy of the boiling heat transfer model. In the present study, an ingenious nucleate boiling heat transfer model was developed on the basis of random fractal function of the bubble sizes distribution, and renormalization group theory was introduced to solve this distribution function. Compared to the previous correlations, the distribution function of bubbles for various sizes can be obtained by solving this random fractal distribution function with renormalization group method. Furthermore, the process of increasing the fractal dimension from 1 to 2 was first proposed in this paper to match the whole evolution of the heated liquid from natural convection to nucleate boiling, to transition boiling, and finally to film boiling. Therefore, the present model can reveal the nature of nucleate boiling more comprehensively and deeply. Through comparison, it can be found that the image of bubble distribution obtained from the random fractal model was very similar to the experimental photographs statistically, and the predictions heat transfer were in good agreement with the experimental data when the superheat ΔT is higher than 10 °C, and the deviation is less than 20%.
       
  • Study on the characteristics of GDL with different PTFE content and its
           effect on the performance of PEMFC
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Tao Chen, Shihua Liu, Jiwei Zhang, Mengnan Tang The content of Polytetrafluoroethylene (PTFE) is the key factor to determine the hydrophobicity and heat transfer characteristics of the gas diffusion layer (GDL), which directly affects the performance of the proton exchange membrane fuel cell (PEMFC). The PTFE content of GDL materials changes due to the complex and variable working conditions and the accumulation of working hours in fuel cells. In order to study the effect of PTFE content and external load on the thermal conductivity of GDL materials, a new method based on Fiber Bragg Grating (FBG) sensing technology was proposed to measure the thermal conductivity of GDL materials. The thermal conductivity of GDL materials with different PTFE content was measured by FBG temperature sensor, and the effect of different PTFE content on the performance of fuel cell was studied. The experimental results show that the hydrophobicity of GDL material increases with the increase of PTFE content, and different PTFE content of GDL materials have different effects on the performance of PEMFC. The difference of thermal conductivity of GDL material with different PTFE content can be measured by using FBG sensing measurement technology, which reflects the change of GDL material properties due to the difference of PTFE content in the GDL material. The results of this study provide guidance for the method of detecting the change of internal material characteristics of PEMFC.
       
  • Some features of solving an inverse problem on identification of material
           properties of functionally graded pyroelectrics
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): A. Vatulyan, S. Nesterov, R. Nedin In the paper, we propose an approach to solving an inverse problem of identifying material characteristics of a functionally graded thermo-piezoelectric body. The operator reciprocity equations of the first kind are obtained in order to solve the problem formulated on the basis of the iterative process. As an example, the inverse problem of thermo-electroelasticity for a pyroelectric rod is investigated. We have carried out the computational experiments on restoration of the rod characteristics with various laws of inhomogeneity including those modeling layered and functionally graded coatings.
       
  • A fractal model of effective thermal conductivity for porous media with
           various liquid saturation
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Xuan Qin, Jianchao Cai, Peng Xu, Sheng Dai, Quan Gan Thermal conduction in porous media has received wide attention in science and engineering in the past decades. Previous models of the effective thermal conductivity of porous media contain empirical parameters typically with ambiguous or even no physical rationales. This study proposes a theoretical model of effective thermal conductivity in porous media with various liquid saturation based on the fractal geometry theory. This theoretical model considers geometrical parameters of porous media, including porosity, liquid saturation, fractal dimensions for both the granular matrix and liquid phases, and tortuosity fractal dimension of the liquid phase. Effects of these geometrical parameters on the effective thermal conductivity of porous media are also evaluated. This proposed fractal model has been validated using published experimental data, compared with previous models, and thus provides a physics-based theoretical model that can provide insight to geoscience and thermophysics studies on thermal conduction in porous media.
       
  • Physical absorption of CO2 and H2S from synthetic biogas at elevated
           pressures using hollow fiber membrane contactors: The effects of Henry’s
           constants and gas diffusivities
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Puttipong Tantikhajorngosol, Navadol Laosiripojana, Ratana Jiraratananon, Suttichai Assabumrungrat The present study applies the mathematical model to investigate the physical absorption of CO2, H2S and CH4 from synthetic biogas at high pressure using hollow fiber membrane contactors. Henry’s constants are considered pressure and temperature dependent, while the polarity of H2S is included in the calculation of gas diffusivities. The model was validated with the experimental data using two hollow fiber membranes, i.e., polyvinylidenefluoride (PVDF) and polytetrafluoroethylene (PTFE), to analyze membrane wetting. The effects of pressure and temperature on the CO2 and H2S absorption and CH4 loss were investigated. From the model validation, the experimental results using PVDF and PTFE at 1 bar are in good agreement with non-wetting mode. At elevated pressures, non-wetting mode results correspond with the experimental results using PTFE, while the partially wetting mode well predicts the results of PVDF. The modeling results also indicate that increasing pressure and reducing temperature improves the absorption fluxes of CO2 and H2S, while the CH4 losses in this work are lower than 5.5%.Graphical abstractGraphical abstract for this article
       
  • Dynamic evolution of the CO2-brine interfacial area during brine
           imbibition in porous media
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Lanlan Jiang, Bohao Wu, Yu Liu, Tetsuya Suekane, Dayong Wang Explicit knowledge on the two-phase interface evolution during CO2 dissolving in brine provides accurate predictions on the subsurface behavior of long-term CO2 storage. In this research, the interfacial areas of CO2-unsaturated brine were dynamically measured during multiphase flow using 3D quantitative analyses. The two-phase interfaces during brine imbibition were divided into three terms based on their attributes, i.e., ganglia, cluster and singlet. The evolution terms of the interfaces were interesting, as their fates showed wide evolution patterns due to the diverging effects of the Reynolds number (fluid velocity × length scale/fluid viscosity) and gravity. The brine bypassed the CO2, and the interface evolved with the development of a priority path under a heterogeneity impact. Relying on the approach of the slice-averaged and volumetric measurement, the effects of forces and heterogeneity on the CO2-unsaturated brine interface were evaluated on different directions. Linear regression of the clouded data points exploited the validity of the power-law distribution from number of trapped cluster to frequency of interfacial area, and the max interfacial areas and variance decreased, while the mean interfacial area increased with brine saturation. Slice-averaged CO2-brine interfacial areas normalized by volume or geometric surface area decreased linearly with the brine saturation at different Reynolds numbers.
       
  • Effective and uniform cooling on a porous micro-structured surface with
           visualization of liquid/vapor interface
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Hyunwoo Noh, Junseon Yoo, Jin-Oh Kim, Hyun Sun Park, Don Koan Hwang, Dong-Pyo Kim, Moo Hwan Kim This study examines cooling efficiency, uniformity, and bubble dynamics on a porous surface. We use infrared (IR) thermometry to visualize results of temperature fields and liquid/vapor interfacial dynamics. Porous and non-porous micro-structured surfaces are prepared using soft-lithography and a ceramic precursor, allylhydropolycarbosilane (AHPCS). The surface cavities promote nucleation, and the heat transfer coefficient on the porous surface is approximately 30% higher than that on the non-porous surface. Additionally, the porous surface exhibits a more uniform temperature field with lower spatial and temporal variations than the non-porous surface. Bubble dynamics is visualized via an IR camera through the bottom side of the test specimens using the IR transparent characteristics of the substrate and micro-structures. The porous surface reveals higher nucleation site density and contact line density and lower equivalent bubble diameter when compared with those of the non-porous surface, and this is consistent with more effective and uniform cooling on the porous surface.
       
  • Modelling sorption equilibria and kinetics in numerical simulations of
           dynamic sorption experiments in packed beds of salt/zeolite composites for
           thermochemical energy storage
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Christoph Lehmann, Olaf Kolditz, Thomas Nagel Composite materials consisting of a salt-impregnated porous host matrix constitute a way to combine the high energy storage density of hygroscopic salts with the fast kinetics of the carrier material. Depending on its pore structure the carrier can furthermore prevent or inhibit leakage of the salt solution. It has been shown experimentally that by impregnation with CaCl2 the heat storage density of zeolite Ca-X can be increased by 53 % to 270 kWh m−3, which confirms the potential of this material class. In transforming this potential into technical heat storage solutions, numerical simulations can support the design process by bridging the gap between material characterization, process specification and reactor design. Such simulations rest, among others, on suitable constitutive relations. For the equilibria and kinetics of salt/zeolite composite sorbents those relations are still missing in the literature. In this work, we present an axisymmetric model of the mass and heat transport through a packed bed of composite sorbent pellets accounting for radial effects such as increased bed void fraction near the sorption chamber walls. Special focus is laid on the modelling of the sorption equilibria and kinetics of CaCl2/zeolite Ca-X composites of various salt loadings. The developed sorption equilibrium model for arbitrary salt loadings of the CaCl2/zeolite Ca-X is based on isotherm measurements of only one composite sample and one sample of pure zeolite Ca-X thereby enabling reduced experimental effort for the equilibrium characterization. The linear driving force kinetics is calibrated using data from dynamic sorption experiments on zeolite Ca-X and used to predict the dynamic sorption behaviour of CaCl2/zeolite Ca-X composites. We found a good predictive capability of the unmodified kinetics model for high inlet humidities—i.e., the practically most relevant cases where the composite plays its strengths. Contrarily, for low inlet humidities, the used kinetics model strongly overestimates the sorption rate, which indicates the presence of additional kinetic inhibition mechanisms under such conditions.
       
  • Identification of nucleate boiling as the dominant heat transfer mechanism
           during confined two-phase jet impingement
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Matthew D. Clark, Justin A. Weibel, Suresh V. Garimella Thermal management of high-power electronics requires cooling strategies capable of dissipating high heat fluxes while maintaining the device at low operating temperatures. Two-phase jet impingement offers a compact cooling technology capable of meeting these requirements at a low pressure drop. Generally, confined impingement geometries are used in electronics cooling applications, where the flow is constrained between the hot surface and orifice plate. Understanding the primary heat transfer mechanisms occurring as boiling takes place on the surface during jet impingement is important, specifically under such confined conditions. In this study, heat transfer from a copper surface is experimentally characterized in both confined jet impingement and pool boiling configurations. The dielectric liquid HFE-7100 is used as the working fluid. For the jet impingement configuration, the jet issues through a single 2 mm-diameter orifice, at jet exit velocities of 1, 3, 6, and 9 m/s, into a confinement gap with a spacing of 3 jet diameters between the orifice and heat source. Additional orifice-to-target spacings of 0.5, 1, and 10 jet diameters are tested at the lowest (Vj = 1 m/s) and highest (Vj = 9 m/s) jet velocities. By incrementing the heat flux applied to the surface and observing the steady-state response at each flux, the single-phase and two-phase heat transfer performance is characterized; all experiments were carried through to critical heat flux conditions. The jet impingement data in the fully boiling regime either directly overlap the pool boiling data, or coincide with an extension of the trend in pool boiling data beyond the pool boiling critical heat flux limit. This result confirms that nucleate boiling is the dominant heat transfer mechanism in the fully boiling regime in confined jet impingement; the convective effects of the jet play a negligible role over the wide range of parameters considered here. While the presence of the jet does not enhance the boiling heat transfer coefficient, the jet does greatly increase single-phase heat transfer performance and extends the critical heat flux limit. Critical heat flux displays a linear dependence on jet velocity while remaining insensitive to changes in the orifice-to-target spacing.
       
  • Mathematical modelling of frequency and force impacts on averaged metal
           flows in alternating magnetic field
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): I.L. Nikulin, A.V. Perminov The averaged quasi-steady flow patterns of metal melt situated in alternating magnetic field are studied numerically. It is taken into account the buoyancy due to non-uniform heating, the intensive radiation heatsink from the melt surface and the Lorentz forces arising in conductor in the alternating magnetic field. The governing equations of the suggested mathematical model are given and the model validations are described. The flow regime maps are plotted based on analysis of melt velocity dependence on the Hartmann number and the parameter of magnetic field diffusion. Flow patterns corresponding each parameter area at the map are given and interpreted. The way of acceleration of melt motion computation is suggested.
       
  • Comments on “‘Combined effects of magnetohydrodynamic and temperature
           dependent viscosity on peristaltic flow of Jeffrey nanofluid through a
           porous medium: Application to oil refinement’ by W.M. Hasona, A.A.
           El-Shekhipy and M.G. Ibrahim, International Journal of Heat and Mass
           Transfer, 2018, 126: 700–714”
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): M.A. Elogail Dear Editor of International Journal of Heat and Mass Transfer,In this letter, I attempt to draw your attention to the fact that the above work that have been published in your highly respectful journal by Hasona et al. (2018) is not original. As the main idea upon which their results have been established is basically plagiarized from another published work and not genuine as the authors claimed. The investigation has been done recently for the first time in the peristaltic literature by Elogail and Elshekhipy (2018). In addition, in the coming few pages, I prove that all the results obtained in Hasona et al. work are significantly incorrect. Also, I elaborate on some of the numerous mistakes in their paper with suggested corrections for your knowledge, as it worth attracting the reader’s attention for such misleading study. Taking into account all the above, I wrote these comments.
       
  • Flow boiling heat transfer in mini channel with serrated fins:
           Experimental investigation and development of new correlation
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Tao Wen, Hongbo Zhan, Dalin Zhang Extensive studies have been conducted on flow boiling heat transfer in mini or micro channels with square and circular configurations. Few investigations, however, have focused on a channel configuration featuring serrated fins. Therefore, the present study experimentally investigated the flow boiling heat transfer characteristics of refrigerant R134a in two mini channels with serrated fins. The equivalent diameters are 1.28 mm with 11 channels and 1.59 mm with 9 channels. Quantitative experiments were conducted under a mass flux of 60–308 kg/(m2.s), heat flux of 6–48 kW/m2, saturation pressure of 0.27–0.45 MPa and vapour quality of 0–1. Flow patterns during flow boiling in the channel were also captured and analysed. Results indicated that in the low vapour quality region, the local heat transfer coefficient increases with both heat flux and saturation pressure. However, the influence of mass flux is related to heat flux. The flow pattern in this region starts with dispersed bubbly flow and develops to vigorous bubbly flow. Slug flow and annular flow are then observed along the flow direction of the refrigerant. In contrast, in the high vapour quality region, the influence of heat flux and saturation pressure seem to vanish and higher refrigerant mass flux corresponds to a greater heat transfer coefficient. The annular flow continues in this region with intermittent dry-out, which leads to a sharp decrease in the heat transfer coefficient. As the existing empirical correlation for calculating flow boiling heat transfer coefficient fails to give a reasonable prediction for the present experimental data, a new correlation was proposed with a mean absolute relation deviation of 15.0% for all 1429 data points. The present experimental data and new proposed correlation can provide meaningful guidance for the design of a mini channel two phase heat exchanger with serrated fins.
       
  • Effect of evaporator tilt on a loop heat pipe with non-condensable gas
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Huanfa Wang, Guiping Lin, Xiaobin Shen, Lizhan Bai, Dongsheng Wen The coupling effect of non-condensable gas (NCG) and evaporator tilts on the steady state operation of a loop heat pipe (LHP) was investigated both experimentally and theoretically in this work. Nitrogen was injected quantitatively into an ammonia-stainless steel LHP to simulate NCG, and the steady state characteristics of the LHP were studied under three typical evaporator tilts. According to the experimental results, the main conclusions below can be drawn. (1) The temperature is the highest under adverse tilt and the lowest under favorable tilt no matter whether there is NCG in LHP. (2) The existence of NCG could cause the increase of temperature under all three typical evaporator tilts, but the temperature increment caused by NCG seems to be relatively small under adverse tilt. (3) The increments of the temperature caused by NCG display different patterns under different tilts. Theoretical analysis was conducted to explain the results: the temperature under the coupling effect of NCG and evaporator tilt was determined by the energy balance between the heat leak from evaporator to compensation chamber and the cooling capacity of returning subcooled liquid. With the increase of heat load, the augmentation of heat leak caused by NCG and the enhancement of subcooled liquid cooling effect were incongruent. The coupling effect of NCG and evaporator tilts should be considered in the terrestrial application of LHP.
       
  • Mass transfer characteristics of CO2 absorption into
           1-butyl-3-methylimidazolium tetrafluoroborate aqueous solution in
           microchannel
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Chunyan Chu, Fanbin Zhang, Chunying Zhu, Taotao Fu, Youguang Ma The mass transfer characteristics of CO2 absorption into aqueous solution of ionic liquid in microchannel was investigated experimentally by a high speed camera. The influences of the ratio of gas and liquid flow rates (QG/QL) and the concentration of ionic liquid on the liquid side volumetric mass transfer coefficient (kLa), liquid side mass transfer coefficient (kL) and length of mass transfer zone (LM) were studied systematically. The results show that both kLa and kL increase but LM decreases with the increasing QG/QL and the concentration of ionic liquid. Taking the enhancement of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) on the mass transfer into account, a dimensionless correlation for predicting kLa was proposed. This work is conducive to the design, optimization and the application of the microchannel reactor for CO2 capture and removal.Graphical abstractGraphical abstract for this article
       
  • Spatio-temporal identification of heat flux density using reduced models.
           Application to a brake pad
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): S. Carmona, Y. Rouizi, O. Quéméner The identification of the spatio-temporal variations of a heat flux density field is addressed in this paper. The developed technique combines the use of reduced models (BERM method) with an iterative method of conjugate gradient descent, for which the gradient is estimated by the adjoint method. The application relates to the identification of the heat flux received by a brake pad in a braking situation, for which the mechanical deformation and the phenomena of wear cause the appearance of hot spots that one seeks to locate. The use of two different Branch bases, one for the temperature field and the other for the heat flux, enable to identify rapidly the time-space variation of the heat flux, without any hypothesis on the spatial form on it.
       
  • Local end-wall heat transfer enhancement by jet impingement on a short
           pin-fin
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): S. Schekman, M.D. Atkins, T. Kim A short pin-fin array has been used to improve the internal cooling characteristics at the trailing edge of some gas turbine blade designs. In such a cooling scheme, the pin-fin array that is sandwiched by the turbine blade’s inner surfaces, experiences a uniform-like coolant stream. The local elevation of internal heat transfer especially on the end-walls (i.e., inner blade surfaces) at the trailing edge is achieved predominantly by horseshoe vortex-type secondary flows whose fluidic behavior has been well established. A modification to this cooling scheme has been made by introducing a blockage upstream, causing multiple jets to impinge on the pin-fins – the blockage jets. Previous studies on the internal cooling scheme employing the blockage jets have assumed that the end-wall flow topology is similar to that formed by the horseshoe vortex-type secondary flows due to similar local heat transfer distributions. However, there is no detailed and sufficient acknowledgement made of the lack of an approaching boundary layer. Therefore, the present study experimentally investigates local heat transfer around a single short pin-fin subjected to a fully turbulent jet impingement simulating the blockage jet impingement and demonstrates that the end-wall flow topology loosely resembles that formed by a horseshoe vortex system and is strictly different, depending on the distance between the jet exit and the pin-fin, relative to the length of the jet’s potential core.
       
  • Passive production of synthesis gas from liquid methanol using a packed
           bed of porous material particles
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Kunito Okuyama, Kanoko Ichimi, Masato Takazawa, Asami Natori, Mikako Tanaka The passive production of synthesis gas from liquid methanol using a packed bed of porous material particles supporting a catalyst is investigated. Heating of the upper portion of a vertical tube packed with the porous particles where the bottom is immersed in liquid methanol is expected to cause steady upward fluid flow due to capillary action enhanced by evaporation. The emergence of a dry region and a resulting increase in temperature can produce synthesis gas due to catalytic reaction, which then flows out of the top end of the tube. In the proposed process, the capillary force, which is dependent on the local liquid content in the porous bed, is balanced locally with the gravitational force and the viscous forces acting on the liquid and vapor. The distributions of the liquid content, flow rates, pressures, and temperatures of liquid and vapor along the tube axis are calculated using a one-dimensional model based on the mass, force, and energy balances for each phase. The experimental results indicate the validity of the process, that is, the induction of steady fluid flow, the emergence of a dry region, temperature increase to the reaction level, and the products of the reacted gases. The behavior of liquid-vapor flow induced by phase-change in a packed bed and the factors that characterize the process and affect the performance are discussed.
       
  • Cascaded lattice Boltzmann method based on central moments for
           axisymmetric thermal flows including swirling effects
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Farzaneh Hajabdollahi, Kannan N. Premnath, Samuel W.J. Welch A cascaded lattice Boltzmann (LB) approach based on central moments and multiple relaxation times to simulate thermal convective flows, which are driven by buoyancy forces and/or swirling effects, in the cylindrical coordinate system with axial symmetry is presented. In this regard, the dynamics of the axial and radial momentum components along with the pressure are represented by means of the 2D Navier-Stokes equations with geometric mass and momentum source terms in the pseudo Cartesian form, while the evolutions of the azimuthal momentum and the temperature field are each modeled by an advection-diffusion type equation with appropriate local source terms. Based on these, cascaded LB schemes involving three distribution functions are formulated to solve for the fluid motion in the meridian plane using a D2Q9 lattice, and to solve for the azimuthal momentum and the temperature field each using a D2Q5 lattice. The geometric mass and momentum source terms for the flow fields and the energy source term for the temperature field are included using a new symmetric operator splitting technique, via pre-collision and post-collision source steps around the cascaded collision step for each distribution function. These result in a particularly simple and compact formulation to directly represent the effect of various geometric source terms consistently in terms of changes in the appropriate zeroth and first order moments. Simulations of several complex buoyancy-driven thermal flows and including rotational effects in cylindrical geometries using the new axisymmetric cascaded LB schemes show good agreement with prior benchmark results for the structures of the velocity and thermal fields as well as the heat transfer rates given in terms of the Nusselt numbers. Furthermore, the method is shown to be second order accurate and significant improvements in numerical stability with the use of the cascaded LB formulation when compared to other collision models for axisymmetric flow simulations are demonstrated.
       
  • Simulation on falling film absorption based on lattice Boltzmann method at
           moderate Reynolds number
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Yuqi Shi, Guangming Chen, Qin Wang, Qi Chen The investigations on heat and mass transfer in the form of falling film flow were mainly focused on the simulation of heat and mass coupling adopting the continuity hypothesis of Navier-Stokes equations. Most of the previous works were done with laminar flow assumptions, or just deal with a very short smooth laminar section beyond the falling film entrance. In this paper, a study investigating the effects of wavy flow on stream absorption by falling liquid film is presented in the perspective of sorption refrigeration process. A multi-phase model lattice Boltzmann method is adopted to simulate the wavy falling liquid film flow, and the absorption process takes place in this flow field region. Absorption simulation was carried out using the laminar flow assumption with the semi-parabolic velocity distribution and the fluctuation results in the LBM simulation. When the overall simulation section is 1 m in length, with initial velocity 0.1 m/s for lithium bromide solution falling film flow, results show that the wave flow has apparent enhancement on heat and mass transfer. Local dimensionless numbers for mass (Sh) and heat (Nu) transfer with waves increase 4 times and 2 times, respectively, compared with the laminar flow.
       
  • Optimized inlet geometry of a laidback fan-shaped film cooling hole –
           Experimental study of film cooling performance
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Marc Fraas, Tobias Glasenapp, Achmed Schulz, Hans-Jörg Bauer The orientation of an internal coolant channel with respect to the external hot gas flow has a major impact on film cooling performance. Previous studies reported a considerable decrease of cooling performance with perpendicular coolant crossflow for a state-of-the-art laidback fan-shaped film cooling hole. The objective of this experimental study is to investigate the extent to which cooling performance in such a setup can be improved by using an optimized cooling hole inlet geometry. For this purpose, three geometries with different cooling hole inlets are investigated. Results are compared to a baseline geometry with a sharp-edged cylindrical inlet. A test rig is used which enables compliance with all relevant non-dimensional parameters. High-resolution infrared measurements are conducted and heat transfer as well as cooling effectiveness are evaluated for up to 50 cooling hole diameters downstream of the cooling hole exit.Results show that the cooling hole inlet geometry tremendously affects cooling performance. Diffuser aerodynamics are altered for all investigated geometries with a modified inlet. This leads to a more symmetrical pattern of the film cooling jet for two of the investigated geometries. As a consequence, film cooling effectiveness is increased compared to the baseline case. The disadvantages of a perpendicular coolant flow in terms of effectiveness are entirely eliminated. Additionally, heat transfer coefficients are lowered. An overall evaluation reveals that the heat flux into the wall is significantly reduced for the proposed optimized cooling hole geometries.
       
  • Parameterising continuum models of heat transfer in heterogeneous living
           skin using experimental data
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Sean McInerney, Elliot J. Carr, Matthew J. Simpson In this work we consider a recent experimental data set describing heat conduction in living porcine tissues. Understanding this novel data set is important because porcine skin is similar to human skin. Improving our understanding of heat conduction in living skin is relevant to understanding burn injuries, which are common, painful and can require prolonged and expensive treatment. A key feature of skin is that it is layered, with different thermal properties in different layers. Since the experimental data set involves heat conduction in thin living tissues of anesthetised animals, an important experimental constraint is that the temperature within the living tissue is measured at one spatial location within the layered structure. Our aim is to determine whether this data is sufficient to reliably infer the heat conduction parameters in layered skin, and we use a simplified two-layer mathematical model of heat conduction to mimic the generation of experimental data. Using synthetic data generated at one location in the two-layer mathematical model, we explore whether it is possible to infer values of the thermal diffusivity in both layers. After this initial exploration, we then examine how our ability to infer the thermal diffusivities changes when we vary the location at which the experimental data is recorded, as well as considering the situation where we are able to monitor the temperature at two locations within the layered structure. Overall, we find that our ability to parameterise a model of heterogeneous heat conduction with limited experimental data is very sensitive to the location where data is collected. Our modelling results provide guidance about optimal experimental design that could be used to guide future experimental studies.
       
  • The effect of fin oscillation in heat transfer enhancement in separated
           flow over a backward facing step
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Saurav Kumar, S. Vengadesan Two-dimensional laminar fluid flow and heat transfer characteristics have been investigated numerically for a oscillating fin mounted on the top wall of backward facing step with constant bottom wall temperature. OpenFOAM is used to solve the governing equation of mass, momentum and energy conservation with the appropriate boundary conditions. Air is used as a working fluid with constant thermo-physical property (Pr = 0.71). It is found that the oscillating fin is the most effective method with highest average Nusselt number and lowest pressure drop, to enhance the mixing and heat transfer when it is compared to the different types of stationary fin arrangement. Further, the effect of frequency (which is directly proportional to the amplitude of velocity) and oscillation have been investigated and found that the average Nusselt number increases with the increase in velocity amplitude. It is also observed that the change in average Nusselt number is negligible with the increase in the amplitude of oscillation for a constant velocity amplitude. A correlation is also presented to express the effectiveness of the fin (ηf) in terms of ratio (Kv) of velocity amplitude (Vo) to the flow velocity (Uf) and is observed to follow the power law with constant exponent as ηf=cKv0.3.
       
  • Flow patterns of vertically upward and downward air-water two-phase flow
           in a narrow rectangular channel
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Vikrant Siddharudh Chalgeri, Ji Hwan Jeong Considering the importance of two-phase flows in narrow rectangular channels and their use in various applications, the hydrodynamics of a co-current air-water two-phase flow in a vertical narrow rectangular channel has been studied. Experiments have been carried out and flow regime maps for vertical upward and vertical downward flows have been plotted based on measured data sets. Flow regimes were identified and classified based on visual observation and void fraction data. Flow visualization was performed using a high speed camera, while a void fraction analysis was done using the electrical impedance method and a digital image analysis. Four different flow patterns were identified for the vertical upward flow and seven flow patterns were identified for the vertical downward flow. The flow regime map for the vertical upward flow was compared with previous studies and also with the flow regime map obtained for the vertical downward flow in this study.
       
  • An analysis of the droplet support fiber effect on the evaporation process
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Christian Chauveau, Madjid Birouk, Fabien Halter, Iskender Gökalp This paper presents an analysis of the effect of the droplet support fiber on the droplet evaporation process. This effect is evaluated for a droplet evaporating in a hot environment at atmospheric pressure using the experimental results of the present study and those in the literature. Selected published results are acquired using similar test conditions and experimental setups as the present data. The only main difference between these studies is the droplet support fiber diameter which varies between 14 µm and 225 µm. The ambient temperature explored in these studies ranges from room temperature up to 973 K. n-Heptane is selected because it is the most common fuel used in these studies. The main findings are that the cross-fiber technique, which uses 14 µm fiber diameters, induces no noticeable heat transfer into the droplet and consequently does not interfere with the evaporation process. In contrast, the classical fiber technique, which uses relatively larger fibers, greatly enhances the droplet evaporation rate as a consequence of increased conduction heat transfer through the fiber. A correlation is proposed to quantify the level of this increase as a function of ambient temperature and the fiber cross-sectional area, df2.
       
  • Numerical investigation on heat transfer of the supercritical fluid upward
           in vertical tube with constant wall temperature
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Zheng Yang, Xu Cheng, Xinghua Zheng, Haisheng Chen The supercritical fluid has been extensively applied in many industry applications and heat transfer characteristics of the supercritical fluid play an important role in system safety and economic design. In this paper, heat transfer characteristics and mechanism of the supercritical fluid upward in vertical tube with constant wall temperature are numerically investigated. Heat transfer fluctuation phenomenon is found at the trans-critical section where fluid experiences the pseudo-critical point. Heat transfer fluctuation takes place only when the wall temperature is higher than the pseudo-critical temperature and the bulk temperature is lower than the pseudo-critical temperature. The traditional prediction correlation can’t predict heat transfer fluctuation at the trans-critical section correctly. Heatflux fluctuation is caused by the buoyancy effect. The buoyancy effect induces the periodic flow variation and the periodic convective heat transfer variation on the radial direction, which determine heatflux fluctuation on the wall. The fluctuation amplitude of heatflux on the wall decreases along the axial direction due to the weakened buoyancy effect. Influence of operating conditions on heat transfer of the supercritical fluid is investigated. R134a is chosen as the working fluid. Operating condition includes mass flow ranging from 500 to 800 kg/(m2 s), inlet temperature ranging from 313.15 to 343.15 K, wall temperature ranging from 403.15 to 433.15 K and operating pressure ranging from 4.35 to 5.04 MPa. It is observed that heat transfer coefficient rises with mass flow, wall temperature and operating pressure increasing, but it doesn’t vary obviously with inlet temperature. Fluctuation amplitude of heat transfer coefficient decreases with mass flow, wall temperature, inlet temperature and operating pressure increasing.
       
  • A new algorithm for solving an inverse transient heat conduction problem
           by dividing a complex domain into parts
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Piotr Duda, Mariusz Konieczny The purpose of this work is to create a new algorithm for solving an inverse transient heat conduction problem in any extended complex domain. If the problem cannot be solved in the entire region under analysis, the domain is divided into parts and free boundary conditions are introduced between them. Then the solution is carried out in subsequent parts of the field. Depending on the shape and dimensions of the analysed part, an appropriate location of the temperature sensors, the amount and size of the control volumes, the time step and a convenient way to filter the temperature distribution over time and space can be proposed. Such actions make it possible to achieve better stabilization of the inverse method and obtain the solution in the whole area. The proposed procedure in subsequent parts of the domain belongs to the group of space marching methods. The analysis starts on the surface where temperature sensors are located and marches through space sequentially to the surface with an unknown boundary condition.The proposed algorithm can be used to optimize the power unit start-up and shutdown operation. It may also enable a reduction in the heat loss arising during the process and extend the power unit life. The presented procedure can be applied in monitoring systems working both in conventional and nuclear power plants.
       
  • An analytical technique for the optimal designs of tube-in-tank thermal
           energy storage systems using PCM
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Yuhang Fang, Jianlei Niu, Shiming Deng Latent heat thermal energy storage (LHTES) using phase change material (PCM) has many application potentials, in view of the fact that it has higher thermal energy storage capacity than the sensible heat thermal energy storage such as stratified water storage (SWS). However, the stored thermal energy in an LHTES system is not all effective in discharging due to the additional heat transfer resistance between PCM and heat transfer fluid (HTF). An LHTES system could have a higher effective storage capacity than an SWS system only if it is well designed. The optimal design of an LHTES system could be realized only after the effective energy storage ratio, Est, is analyzed in the design stage. In comparison to the laborious computational analysis method, in this work, we developed an analytical technique from the effectiveness-NTU theory to calculate the required heat transfer length and predict Est of the basic unit in any tube-in-tank LHTES system. The technique was first compared with the numerical simulation method we reported earlier, and then used to find the optimal design under various constraints. It was shown that heat transfer enhancement in PCM could effectively improve the effective storage capacity of an optimal design. However, the maximum Est was limited by the thermal resistance in HTF when the enhancement in PCM was over a certain threshold. It was demonstrated that the use of HTF in a low-Re turbulent region could enhance heat transfer in HTF and achieve an Est as high as that in a laminar region while obtaining a higher discharging rate if heat transfer in PCM was well enhanced. This analysis provided quantitative guidelines on designing optimal tube-in-tank LHTES systems.
       
  • Ice formation modes during flow freezing in a small cylindrical channel
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Aakriti Jain, Ankur Miglani, Yonghua Huang, Justin A. Weibel, Suresh V. Garimella Freezing of water flowing through a small channel can be used as a nonintrusive flow control mechanism for microfluidic devices. However, such ice valves have longer response times compared to conventional microvalves. To control and reduce the response time, it is crucial to understand the factors that affect the flow freezing process inside the channel. This study investigates freezing in pressure-driven water flow through a glass channel of 500 μm inner diameter using measurements of external channel wall temperature and flow rate synchronized with high-speed visualization. The effect of flow rate on the freezing process is investigated in terms of the external wall temperature, the growth duration of different ice modes, and the channel closing time. Freezing initiates as a thin layer of ice dendrites that grows along the inner wall and partially blocks the channel, followed by the formation and inward growth of a solid annular ice layer that leads to complete flow blockage and ultimate channel closure. A simplified analytical model is developed to determine the factors that govern the annular ice growth, and hence the channel closing time. For a given channel, the model predicts that the annular ice growth is driven purely by conduction due to the temperature difference between the outer channel wall and the equilibrium ice-water interface. The flow rate affects the initial temperature difference, and thereby has an indirect effect on the annular ice growth. Higher flow rates require a lower wall temperature to initiate ice nucleation and result in faster annular ice growth (and shorter closing times) than at lower flow rates. This study provides new insights into the freezing process in small channels and identifies the key factors governing the channel closing time at these small length scales commonly encountered in microfluidic ice valve applications.
       
  • Sensitivity analysis and application of machine learning methods to
           predict the heat transfer performance of CNT/water nanofluid flows through
           coils
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Alireza Baghban, Mostafa Kahani, Mohammad Alhuyi Nazari, Mohammad Hossein Ahmadi, Wei-Mon Yan Nowadays, nanofluids are broadly utilized for various engineering and industrial systems including heat exchangers, power plants, air-conditioning, etc. The helically coiled tube heat exchangers are of the most interesting and efficient kinds of heat exchangers. The current study has focused on proposing model to predict Nusselt number by considering Prandtl number, volumetric concentration, and helical number of helically coiled heat exchanger as input variables. The investigated heat exchanger utilizes water carbon nanofluid. To propose an accurate model, a multilayer perceptron artificial neural network (MLP-ANN), adaptive neuro-fuzzy inference system (ANFIS), and least squares support vector machine (LSSVM) models are used. 72 experimental data are utilized as input data. Results indicate that LSSVM approach has the best performance and the proposed model by this approach has R-squared value equals to 1.
       
  • Validation of numerical models for cryogenic-liquid pool spreading and
           vaporization on solid ground
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Le-Duy Nguyen, Myungbae Kim, Byungil Choi, Kyungyul Chung Accidental spills of cryogenic liquids create vaporizing pools spreading over the ground that can result in pool fires, explosions, or hazardous vapor clouds. Various integral models have been developed for simulating the spread and vaporization of cryogenic liquid pools. The spreading law of a constant Froude number (CFN1), which was originally derived for floating pools on water, has been assumed to be accurate for pools spreading on land in some models. This assumption is controversial and has not been validated. In addition, although the gas accumulation over spreading pools (GASP2) model has been well developed, further validation is required. An attempt was made to fill these gaps. This study aimed to propose and validate numerical models, i.e., a model incorporating the spreading law of a constant Froude number (CFN model) and simplified GASP models for indoor spills. The results were compared to the experimental data of cryogenic liquid pools spreading on solid ground. A good agreement between the predictions obtained from the simplified GASP models and the measured data was shown. Conversely, the CFN model yielded unrealistic results. Then, a modified CFN model was proposed and validated. The validations suggested that the modified CFN and simplified GASP models successfully simulated the behavior of cryogenic liquid pools spreading on solid ground.
       
  • Phonon backscatter, trapping, and misalignment effects on microscale
           thermal conductance below the Casimir limit
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Francis G. VanGessel, Peter W. Chung At nanometer to micron length scales, there exists a strong competition between intrinsic and extrinsic scattering mechanisms that can curtail the free flight of phonons and ultimately affect the thermal transport. Despite significant progress in showing the ability to reach behaviors significantly below the Casimir limit, little appears to be understood about the competition between these scattering sources. In this investigation, we propose a simple one-parameter geometry that simultaneously modulates backscattering and trapping effects to enable directed study of these different means of controlling phonons. The geometry is a simple sequence of chambers offset from one another by a defined distance. We use the geometry to study the effects of phonon backscatter, trapping, and corner-turning on the thermal conductance in Si nanowires (NWs). We employ a full Brillouin zone Boltzmann Transport Equation (BTE) method to determine spatially-varying phonon densities in the geometry. Significantly greater impact is seen due to backscatter than any other means of arresting phonon flow. By creating a geometry that maximizes backscatter, a roughly 8-fold reduction in thermal conductance below the Casimir limit can be achieved at room temperature which is a factor of four smaller than the nearest reported value in the literature. The geometry is also useful for systematic investigation of other means of controlling phonons and affecting thermal transport; particularly, we investigate diffuse versus specular boundary scattering and the induced misalignment between the phonon flow and thermal flux due to the shape of the geometry. These effects combine to offer new insights into fundamental phonon behaviors and possible routes to phonon control.
       
  • An experimental study on the effects of frosting conditions on frost
           distribution and growth on finned tube heat exchangers
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Long Zhang, Yiqiang Jiang, Jiankai Dong, Yang Yao, Shiming Deng Recently, the authors have published a paper which provided the frost distribution and growth along the airflow direction of finned tube heat exchangers (FTHXs), and demonstrated that some frost was accumulated on the edge of windward fins at a given frosting condition. As a follow-up to the work reported in the previous paper, in the current paper, the effects of frosting conditions on frost distribution and growth characteristics of FTHXs with different fin pitches were experimentally investigated. The results showed that the protruded thickness of frost on the edge of windward fins and the ratio of the frost mass on the edge of windward fins to that on the entire FTHX were both increased with the increases in air temperature (Ta) and relative humidity (RHa), but decreased with an increase in initial air face velocity (va). In addition, the effects of RHa on the mass ratio were more significant than those of Ta and va. Furthermore, the averaged frost density on the edge of windward fins was increased with an increase in RHa; and that on the surfaces of fins and tubes was increased with an increase in va, but decreased with an increase in RHa.
       
  • Influence factors of the evaporation rate of a solar steam generation
           system: A numerical study
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Jinxin Zhong, Congliang Huang, Dongxu Wu, Zizhen Lin Many efforts have been dedicated to improve the solar steam generation by using a bi-layer structure. In this paper, a two-dimensional mathematical model describing the water evaporation in a bi-layer structure is firstly established and then the finite element method is used to simulate the effects of different influence factors on the evaporation rate. Results turn out that: besides the high solar energy absorptivity of the first-layer, an optimum porosity of the second-layer porous material should be applied and the optimum porosity is about 0.45 in this work. This optimum porosity is determined by the balance between the positive effect of the lowering effective thermal conductivity of the second layer and the negative effect of the reduced vapor diffusivity in the second layer when the porosity is decreased. The influence of the thermal conductivity of the second-layer porous material is negligible because the effective thermal conductivity of the second layer is determined by the porosity while a larger porosity means more water in the second layer. The ambient air velocity could greatly enhance the evaporation rate, and the evaporation rate will decrease linearly with the increase of the air relative humidity. This study is expected to supply some information for developing a more effective bi-layer solar steam generation system.
       
  • Experimental investigation of condensation heat transfer and pressure drop
           of R-134a flowing inside dimpled tubes with different dimpled depths
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Kanit Aroonrat, Somchai Wongwises An experimental investigation is conducted to determine the effect of dimpled depth on the condensation heat transfer coefficient and pressure drop of R-134a flowing inside dimpled tubes. The test condenser is a double tube heat exchanger where the refrigerant flows inside and water flows in the annulus. The inner tube is a 1500 mm long and 8.1 mm inside diameter. The experiments are carried out for one smooth tube and three dimpled tubes having dimpled depth of 0.5, 0.75, and 1.0 mm. For each test tube, several test runs are performed over mass flux range of 300–500 kg/m2s, heat flux range of 10–20 kW/m2, and condensing temperature range of 40–50 °C. The experimental results reveal that the dimpled tube presents the significant heat transfer enhancement and pressure drop penalty. The tube with the highest dimpled depth yields the highest heat transfer enhancement and pressure drop penalty up to 83% and 892% higher than those of the smooth tube, respectively. Additionally, the overall performance of dimpled tube is evaluated in term of efficiency index. The new correlations including the effect of dimpled depth, dimpled pitch, and helical pitch on the Nusselt number and friction factor of R-134a in dimpled tube are developed.
       
  • Experimental research on condensation of R134a and R404A refrigerants in
           tubular mini-channels during impulsive instabilities. Part II
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Waldemar Kuczynski The following paper presents the results of experimental research on the condensation of R134a and R404A refrigerants in tubular mini-channels during impulsive hydrodynamic instabilities. The first part includes an analysis of the influence of impulsive instabilities on the development of the condensation phase-change of R134a and 404A refrigerants in horizontal tubular mini-channels. The second part will present results of research on the same type of instabilities during the decay of the condensation phase-change process of R134a and 404A refrigerants. This research was conducted using the same set of investigated mini-channels with internal diameters of D = 0.63–3.30 mm. Special attention was paid to the possible occurrence of characteristic instabilities during condensation in mini-channels, so-called capillary blocking.
       
  • Effects of magnetic field on the pool boiling heat transfer of water-based
           α-Fe2O3 and γ-Fe2O3 nanofluids
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Shi-Yan Li, Wen-Tao Ji, Chuang-Yao Zhao, Hu Zhang, Wen-Quan Tao Pool boiling experiments of water-based α-Fe2O3 and γ-Fe2O3 nanofluids with different concentrations (0.005–0.100 g/L) were conducted at atmospheric pressure. Two kinds of magnetic field induced by two neodymium magnets were also applied to investigate the effects of magnetic field on the pool boiling of nanofluids. It demonstrated that the magnetic field could change the local concentration of nanofluids and produce an extra pressure on the bubble boundary. The extent of the effects was not only dependent on the intensity and distribution of magnetic field, but also the magnetism and concentration of nanoparticles. For the 0.050 g/L γ-Fe2O3 nanofluid in the presence of magnetic field induced by two mutually exclusive magnets, an enhancement in boiling heat transfer coefficient up to 28% was obtained. The results of the experiments indicated the feasibility to control the pool boiling performance of magnetic nanofluids by external magnetic field.
       
  • Experimental research on condensation of R134a and R404A refrigerants in
           mini-channels during impulsive instabilities. Part I
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Waldemar Kuczynski The following paper presents the results of experimental research on the condensation of R134a and R404A refrigerants in horizontal tubular mini-channels during impulsive hydrodynamic instabilities. Due to the complexity of the problem, it will be presented in two parts. The first part covers the results of experimental research on the influence of impulsive instabilities during the development of condensation of R134a and R404A refrigerants in mini-channels. The second part will cover the decay of condensation for similar conditions. The paper also provides a definition and conditions of the initiation and propagation of impulsive instabilities. Special attention was paid to the possible occurrence of characteristic instabilities during condensation in mini-channels, so-called capillary blocking.The experimental investigation was based on the condensation of R134a and R404A refrigerants in horizontal tubular mini-channels with internal diameters of D = 0.64; 0.90; 1.40; 1.44; 1.92; 2.30 and 3.30 mm. Propagation of impulsive instabilities was a result of a sudden change in the refrigerant flow-rate inside mini-channels.
       
  • Air-side heat transfer enhancement in plate-fin channel with an
           airfoil-based self-agitator
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Kuojiang Li, Xianchen Xu, Zheng Li, Hsiu-Hung Chen, YangYang Chen, Sheng Wang, Zhaoqing Ke, Guoliang Huang, Chung-lung Chen, Chien-Hua Chen Airfoil-based self-agitators (AFAs) were installed in multiple plate-fin channels integrated with cantilever beams. The heat transfer enhancement and pressure drop characteristics of this AFA design were experimentally investigated and compared with the clean channel case. We found that the AFA vibrates periodically and generates vortices, which enhance flow mixing and thus heat transfer performance. A rectangular shaped airfoil-based self-agitator (RAFA) and a delta shaped airfoil-based self-agitator (DAFA) with variable chord lengths were designed to investigate shape and size effects on thermal performance. Measurements were also carried out for DAFAs with different layouts, such as multiple rows of DAFAs installed inside a single channel. For the chosen heat sink and assigned working conditions, the best heat transfer performance was obtained with four rows of DAFAs, which caused an 80% increase in overall Nusselt number over the clean channel at the same Reynolds number and a 50% rejected heat increase at the same pumping power due to the strong longitudinal vortices generated by the presence of the AFAs.
       
  • Gravity effects on subcooled flow boiling heat transfer
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Michel T. Lebon, Caleb F. Hammer, Jungho Kim Subcooled flow boiling measurements using HFE-7000 were obtained in a vertical 6 mm ID sapphire tube during upward and downward flow at various gravity levels including hypergravity and microgravity. Temperature sensitive paint (TSP) applied to the inside of the tube was used to measure time and space resolved temperature and heat transfer distributions at the wall–fluid interface, and this data along with flow visualization were used to characterize the heat transfer for different flow patterns. Time-averaged heat transfer coefficients were compared at nine gravity levels, four mass fluxes, six heat fluxes, and two subcoolings. The average heat transfer coefficient typically increased with heat flux, mass flux, and absolute gravity level. In microgravity, the lack of mixing at low heat fluxes due to the absence of natural convection and bubble slip velocity resulted in a decrease in heat transfer coefficient compared to downward and upward conditions. The heat transfer was strongly dependent on the flow regime, causing certain data points at high mass flux or low gravity to deviate from the typical trends due to deactivation of nucleation sites. The heat transfer coefficient became less dependent on gravity as the mass flux and heat flux increased. Flow regimes were very sensitive to the competition between buoyancy and inertial forces, which in turn affected the heat transfer. Mechanisms by which heat is transferred under various conditions are discussed.
       
  • Effects of temperature-dependent properties on natural convection of
           power-law nanofluids in rectangular cavities with sinusoidal temperature
           distribution
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Lei Wang, Changsheng Huang, Xuguang Yang, Zhenhua Chai, Baochang Shi In this paper, the effects of temperature-dependent properties on natural convection of nanofluids in rectangular cavities with sinusoidal temperature distribution are investigated in detail with lattice Boltzmann method. To improve the computational efficiency, all simulations are performed on the Graphics Processing Unit (GPU) using NVIDIA’s CUDA. The fluid in the enclosure is a water-based nanofluid containing Al2O3 nanoparticles. The effects of power-law index (0.5⩽n⩽1.5), thermal Rayleigh number (104⩽Raf⩽106), diameter of nanoparticle (25nm⩽ds⩽100nm), nanoparticle volume fraction (0.0⩽ϕ⩽0.04), temperature of the cooled sidewall (315K⩽Tc⩽335K), temperature difference between the sidewalls (10K⩽ΔT⩽50K), amplitude ratio (0.0⩽A⩽1.0), wave number (0.0⩽ω⩽6.0), phase deviation (0.0⩽θ⩽π) and aspect ratio (0.250⩽AR⩽4.00) on heat and fluid flows are investigated. The results reveal that there is an optimal volume fraction ϕopt at which the maximum heat transfer enhancement is obtained, and the value of ϕopt is found to increase slightly with decreasing the nanoparticle diameter, and to increase remarkably with increasing the temperature of Tc or ΔT. In addition, the average Nusselt number is generally decreased with increasing power-law index, while increased with increasing A and ω. Further, we found that the average Nusselt number behaves nonlinearly with the phase deviation parameter. Moreover, the present results also indicate that there is an optimal value of aspect ratio at which the impact of AR on heat transfer is the most pronounced.
       
  • A new modelling method for superalloy heating in resistance furnace using
           FLUENT
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Zhenglong Fu, Xinhong Yu, Huaili Shang, Zhenzhen Wang, Zhiyuan Zhang The simulation of heating process of superalloys is of great significance to predict the temperature distribution and equilibration time of workpiece. In this paper, a new method was proposed to simulate the heating process of superalloy billet in resistance furnace for all strategies of thermal schemes using commercial CFD software FLUENT. In the model, numerical analysis of natural convection and surface thermal radiation in a chamber electric furnace having heat-conducting solid walls of finite thickness with a heat source located in the side and top walls of the furnace in conditions of convective heat exchange with environment has been carried out, and such conjugate heat transfer process was solved by FLUENT solver. Furthermore, a PID methods was proposed to control the energy source of the resistance wires based on FLUENT UDF, in order to regulate the furnace temperature according thermal scheme. This model was validated through temperature measurement experiment in a small chamber resistance furnace. Compared with the measured data, the model was adequate for predicting the temperature profile and equilibration time of superalloy.
       
  • Optical properties and transmittances of ZnO-containing nanofluids in
           spectral splitting photovoltaic/thermal systems
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Liang Huaxu, Wang Fuqiang, Li Dong, Zhu Jie, Tan Jianyu As ZnO nanoparticles had the advantages of high thermal conductivity and low cost, the possibility of using ZnO nanoparticles in spectral splitting photovoltaic/thermal (PV/T) systems was initially studied from the perspective of optical properties. Water–ZnO and glycol–ZnO nanofluids were prepared via a two-step method and used for model validation and stability testing. The scheme employed to investigate the optical properties and radiative transfer of the nanofluids was developed using Mie scattering theory combined with the Monte Carlo ray tracing (MCRT) method. The overall effective spectral transmittance coefficients of PV cells were utilized for comprehensive evaluation of the spectral transmittances of the nanofluids in spectral splitting PV/T systems. The overall effective spectral transmittance of a PV cell water-ZnO nanofluids was 21.54% higher than that those of cells containing water–polypyrrole and water–Cu9S5 nanofluids, respectively. The effects of the nanoparticle diameter, mass concentration and the optical length of the nanofluid on the spectral transmittance of glycol–ZnO nanofluid were also investigated.Graphical abstractSpectral transmittance comparison of among water-ZnO nanofluid, water-Cu9S5 nanofluid, and water- polypyrrole nanofluid.Graphical abstract for this article
       
  • Investigation on optimization of the thermal performance for compressible
           laminar natural convection flow in open-ended vertical channel
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Deboprasad Talukdar, Chung-Gang Li, Makoto Tsubokura The present paper focuses on the optimization of the thermal performance for compressible laminar natural convection flow induced under high-temperature difference in an open-ended vertical channel by optimizing the channel inter-plate spacing using numerical simulation. The present investigation is conducted for a wide range of Rayleigh number (Ra) 104 to 107 in channel heated asymmetrically by uniform surface temperature with air (Pr0.72) as working fluid. Several values of channel gap between plates, new modified preconditioned all-speed Roe scheme along with dual time stepping technique and modified Local One-dimensional Inviscid (LODI) relations as channel inlet and outlet boundary conditions suitable for compressible laminar natural convection is employed for the current simulation. Heat transfer rate in terms of average Nusselt number is obtained for all Rayleigh number and channel aspect ratio is obtained. Variation of thermal and velocity profiles, the variation of average Nusselt number and mass flow rate into the channel for the combination of each Rayleigh number and channel aspect ratio is reported. From the results obtained, a correlation for optimum aspect ratio with Rayleigh number which maximizes the heat transfer within the channel is presented.
       
  • Thermohydraulic performance of microchannel heat sinks with triangular
           ribs on sidewalls – Part 2: Average fluid flow and heat transfer
           characteristics
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Lei Chai, Liang Wang, Xin Bai Triangular ribs mounted in the microchannel heat sink generally result in higher heat transfer coefficient, but are usually accompanied by higher pressure drop per unit length. In order to obtain some insight into the effect of geometry parameters of triangular ribs on laminar flow and heat transfer characteristics, three-dimensional conjugated heat transfer models taking account of the entrance effect, viscous heating and temperature-dependent thermophysical properties are conducted, and four non-dimensional variables related to the width, height, converging-diverging ratio and spacing of the triangular rib for both aligned and offset arrangements are designed. Effects of the geometry and arrangement of triangular ribs on thermohydraulic performance are examined by the variations of average friction factor and Nusselt number for Reynolds number (Re) ranging from 187 to 715. The studied microchannels have the same width (Wc) of 0.1 mm and same depth (Hc) of 0.2 mm in the constant cross-section region. The geometric parameters of aligned or offset triangular ribs are ranged in 0.025–0.4 mm for width (Wr), 0.005–0.025 mm for height (Hr), 0.2–5 mm for spacing (Sr) and 0–1 for the width ratio of converging region to a single rib (Wcon/Wr). Based on the total 660 computational cases of the microchannel heat sinks with triangular ribs, the correlations of average friction factor and Nusselt number are proposed, respectively for aligned and offset arrangements. For the studied Reynolds number range and geometry parameters of flow passage, the microchannel heat sinks with aligned triangular ribs present 1.03–2.01 times higher of average Nusselt number and 1.06–9.09 times larger of average friction factor, and those with offset triangular ribs show 1.01–2.16 times higher of average Nusselt number and 1.04–7.43 times larger of average friction factor, compared with the reference straight microchannel heat sink. Proposed heat transfer and friction factor correlations show good agreements with the computational results for the microchannel heat sinks within the parameter ranges of 187 ≤ Re ≤ 715, 0.25 ≤ Wr/Wc ≤ 4, 0.05 ≤ Hr/Wc ≤ 0.25, 0 ≤ Wcon/Wr ≤ 1, and 2 ≤ Sr/Wc ≤ 50.
       
  • Experimental evaluation of transient heat and mass transfer during
           regeneration in multilayer fixed-bed binder-free desiccant dehumidifier
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Jubair A. Shamim, Soumyadeep Paul, Kenji Kitaoka, Wei-Lun Hsu, Hirofumi Daiguji In this study, regeneration experiments were performed in a previously developed multilayer fixed-bed, binder-free desiccant dehumidifier (MFBDD) in order to investigate the transient heat and mass transfer characteristics during the desorption of condensed water from desiccant material inside the device. A microsphere silica gel (M.S.GEL manufactured by AGC Si-Tech. Co., Ltd., Japan) having a pore diameter of 2.7 nm was used as the desiccant, which was feasible for regeneration at a temperature slightly above 50 °C. To prevent heat loss during regeneration, the test section was placed inside a constant-temperature oven. Experiments were performed under several regeneration conditions to investigate the influence of temperature, humidity, and flow velocity of the regeneration air on the heat and mass transfer characteristics of the device. The influence of heat loss from the test section to the surroundings during regeneration was also determined by precisely controlling the oven temperature. The results revealed that the regeneration capacity of the device improved with an increase in the regeneration air temperature. However, the maximum temperature of regeneration air should be optimized for energy-efficient operation of the device according to the regeneration conditions.
       
  • Carbon/carbon high thickness shell for advanced space vehicles
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): M. Albano, O.M. Alifanov, S.A. Budnik, A.V. Morzhukhina, A.V. Nenarokomov, D.M. Titov, A. Gabrielli, S. Ianelli, M. Marchetti The aim of this paper is to study a shell structure for space applications. The aim of the structure is to be reusable and thick. This first study will focus on thermal environment. Starting from a defined geometry, a prototype will be manufactured. Thermo-structural behavior of the structure will be analyzed by numerical analysis and tests. Thermal properties, such as thermal conductivity and heat capacity, will be studied by the use of the inverse method. A robust numerical approach, such as inverse method, is one of the best for this problem as many parameters concur for the determination of properties. Such approach permits to perform the parametric and structural identification of the model. These procedures are presented including both experimental investigation and methodical-numerical aspects. Special test equipment and the regularizing algorithm for solving the ill-posed inverse heat conduction problem are described. In the frame of thermal properties determination, a verification and prediction of thermocouple error will be performed. Developed in the frame of this work the experimental and theoretical methodology for complex data acquisition of unsteady thermal state of the prototype of shell structure is proposed.
       
  • A decoupling penalty finite element method for the stationary
           incompressible MagnetoHydroDynamics equation
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Jien Deng, Zhiyong Si In this paper, we give a penalty finite element method for the steady MHD equations. In this method, we decouple the MHD into two equations, one for the velocity and magnetic (u,B), the other for the pressure p. We prove the existence of the penalty method and the optimal error estimate. Then, we give the penalty finite element method for the MHD equations. The stability analysis shows our method is stable, and the error estimate shows our method has an optimal convergence order. Finally, we give some numerical results of exact solution equation and Hartmann flow. The numerical results show that our penalty finite element method is effect.
       
  • Efficient uncertainty quantification of stochastic heat transfer problems
           by combination of proper orthogonal decomposition and sparse polynomial
           chaos expansion
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Arash Mohammadi, Mehrdad Raisee To increase the contribution and reliability of computational fluid dynamics efforts in design process of industrial equipments, it is necessary to quantify the effects of uncertainties on the system performance. Due to exponentially increment of the computational cost with number of uncertain variables for uncertainty quantification using classical polynomial chaos expansion methodology, reducing the required number of samples for uncertainty quantification is a real engineering challenge. In this paper, the proper orthogonal decomposition method based on the multifidelity approach is combined with the full and sparse polynomial chaos expansions for efficient uncertainty quantification of complex heat transfer problems with large number of random variables. The conjugate conduction heat transfer in NASA C3X cooled gas turbine blade with geometrical uncertainties and the convective heat transfer in ribbed passage with the stochastic wall heat flux boundary condition are considered as the test cases. Results of uncertainty quantification analysis in both test cases showed that proposed multi-fidelity approaches are able to produce the statistical quantities with much lower computational cost compare to the classical regression-based polynomial chaos method. It is shown that the combination of the proper orthogonal decomposition with the sparse polynomial chaos gives a computational gain at least 2 times greater than combination of the proper orthogonal decomposition with the full polynomial chaos expansion.
       
  • Performance of pool boiling with 3D grid structure manufactured by
           selective laser melting technique
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Chi Zhang, Li Zhang, Hong Xu, Pei Li, Bo Qian 3D thin wall grid structures were manufactured with selective laser melting (SLM) technique for boiling enhancement. To precisely control the structure parameters and investigate their influences on boiling heat transfer characteristics, the scan line spacing method was adopted to manufacture various grid width and wall height structures. The stainless steel was chosen as the building material. Pool boiling experiment results showed that grid structures could significantly influence nucleate boiling behavior and enhance critical heat flux (CHF). The nucleate boiling heat transfer coefficient generally decreased with grid width except for the 0.4 mm grid width samples, the grid channels of which were blocked. The decrease trend was caused by the decreasing effective heating area. The CHF increased with grid width until 1.1 mm, then slightly decreased when the grid width was greater than 1.1 mm. The maximum CHF on the grid structure surface achieved at the transition point was 303 W/cm2, which was three times that of the plain surface. The enhancement was attributed to the grid structure’s “partition effect” that inhibited Helmholtz instability, confined bubble and hot spot expansion in the near surface region. The results provide important guidance for the design of future 3D structured surfaces for boiling enhancement. SLM technique provides a new and effective way for the manufacturing of innovative structured surfaces with controllable parameters and opens a new direction for boiling heat transfer mechanism research.
       
  • Component level modelling of heat transfer during vapour phase soldering
           with finite difference ADI approach
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): István Bozsóki, Attila Géczy, Balázs Illés In this paper, the complex heat transfer process of the vapour phase soldering has been investigated on the level of electronic components. VPS is gaining increased attention lately, and the process needs alternative approaches in modelling, compared to conventional soldering processes in electronics mass manufacturing. Component level modelling was not studied deeply in the literature before, so our focus pointed to heat transfer on large size surface mounted electronic components. Applying the Fourier type heat conduction equation, a detailed 3D thermal model of a polyester capacitor on a printed circuit board was implemented, based on X-ray images of an actual assembly. Our model incorporates inner geometry, material inhomogeneity, composite materials and anisotropic thermal conductivity as important thermal features. Transient heating was calculated with Finite Difference Method combining an alternating direction implicit (ADI) approach, using averaged heat transfer coefficient. Validation measurements were performed in our experimental VPS system. The measured data show good agreement with the calculation results and points to possible application for use in advanced engineering and manufacturing environment.
       
  • Electrostatic-induced coalescing-jumping droplets on nanostructured
           superhydrophobic surfaces
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): B. Traipattanakul, C.Y. Tso, Christopher Y.H. Chao Coalescing-jumping droplets from the condensation of water vapor on a non-wetting surface return to the substrate due to resistance forces. While some can coalesce with neighboring droplets and jump again, some adhere to the surface and become larger, leading to progressive flooding, limiting heat transfer performance. To address these issues, an electric field is utilized. This study investigates the jumping height, the droplet charge, the jumping angle, the gravitational force, the drag force, the inertia force and the electrostatic force of coalescing-jumping droplets in electric fields through experiment and mathematical models. The results show that an electric field can enhance the jumping height due to a significant increase in the electrostatic force. With the applied electric field, the maximum jumping height is over three times higher than those without. Additionally, the study reports the intersection point at the jumping droplet radius of 35 μm separating jumping droplet motion into two regimes; the drag-force-dominated regime where the small-sized droplets can jump and reach the top plate, and the gravitational-force-dominated regime where the larger droplets can jump, but return to the substrate. The other intersection point is between the gravitational force and the inertia force showing a decrease in the influence of the inertia force with a greater applied electric field. Moreover, it is also found that the average charge of the droplets is relatively constant in all pressure conditions and applied electric fields. The results of these findings can further advance knowledge on the enhancement of heat transfer and can be applied to several applications including self-cleaning, smart windows, thermal diodes and condensation heat transfer enhancement.
       
  • A lattice Boltzmann model for multi-component two-phase gas-liquid flow
           with realistic fluid properties
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Hao Deng, Kui Jiao, Yuze Hou, Jae Wan Park, Qing Du Multi-component multi-phase flows are of significant interests in nature and engineering problems of different fields. Modeling the phenomena involved in multi-phase flows is challenging, attributed to the complexity in simulating phase interface dynamics and diffusion processes. Owing to its kinetic nature, lattice Boltzmann (LB) method emerges as an attractive computational approach, in dealing with complicated fluid flow problems and microstructure geometries with effectiveness of parallelized processing. However, some critical drawbacks of basic multi-phase LB models, such as the low density and kinematic viscosity ratios, thermodynamic inconsistency, and dependence of surface tension and density distribution on relaxation times, limit its application in realistic multi-component multi-phase systems. Based on the original pseudopotential model and progresses in single-component multi-phase model, a multi-component LB model was proposed to study the two-phase gas-liquid flow with realistic fluid properties. The importance of improved model is in simultaneously realizing the realistic fluid flow characteristics for multi-component two-phase system, including high density and viscosity ratios, good thermodynamic consistency, independently tunable surface tension and appropriate two-phase boundaries. The proposed LB model is validated with Laplace law and visualization experiment results, and the effects of surface tension, gas flow velocity and wall wettability on dynamic behaviors of fluid flow are investigated.
       
  • Optimization of influence factors for water cooling of high temperature
           plate by accelerated control cooling process
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Hwan Suk Lim, Yong Tae Kang The accelerated control cooling is considered to be one of the most practical technologies in the high tensile strength steel manufacturing industry. In order to achieve a high precision required for the cooling process, the system modeling should be done and optimized by considering the heat transfer mechanism as much as possible. For the system optimization, the parametric analysis for the influence factors such as feed water temperature, plate speed, plate width and specific heat should be carried out. In this study, we focus on optimizing the influence factors during water cooling of high temeperature plate by the accelerated control cooling process. The scale analysis with Reynolds and Prandtl numbers is made to optimize the effect of feed water temperature, and then the water flow density is determined during the water cooling process. The cooling efficiency is calculated in order to optimize the plate speed and plate width. Finally, start cooling temperature(SCT) and finish cooling temperature(FCT) are optimized by comparing the specific heat of standard references about low carbon steel such as NIST-JANAF, Eurocode, ISIJ. It is concluded that the accuracy of the predicted finish cooling temperature and the stability of the cooling process are significantly improved after the optimization of influence factors.
       
  • Analytical solutions and numerical simulations of radiative property in
           the two-layer concentrically spherical large particle
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Keyong Zhu, Shaoling Li, Yong Huang This paper quantified systematically light transfer through the two-layer concentrically spherical large particle with specular or diffuse interfaces. Analytical solutions predicted the absorptance, scattering albedo and Monte Carlo ray-tracing method was used to predict the absorptance and scattering phase function. The effects of (i) the size parameter, (ii) refractive indices, (iii) absorption indices, and (iv) the diameter ratio of the outer and inner spheres on the absorptance and scattering phase function of the two-layer concentrically spherical particle were investigated. The size parameter and absorption indices increased the absorptance for either specular or diffuse interfaces due to the stronger absorption in the two-layer concentrically spherical particle. Moreover, the refractive index of the outer sphere increased the forward scattering for specular interfaces, and scattering phase function was almost independent of the refractive indices and diameter ratio of outer and inner spheres for diffuse interfaces.
       
  • Ultra-high heat flux dissipation with Piranha Pin Fins
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Corey Woodcock, Chisela Ng'oma, Michael Sweet, Yingying Wang, Yoav Peles, Joel Plawsky The Microfluidic, Extreme heat flux, CMOS compatible, Heat-eXchanger (MECH-X) is an embeddable silicon-based reactor-style heat sink which has been experimentally studied by the authors. The 800 µm thick MEMS heat sink discretizes the working fluid into stacked primary and secondary chambers to enhance phase change heat transfer. Piranha Pin-Fin (PPF) microstructures—reported previously by the authors—have been employed in the primary reaction chamber. The PPF structures vent higher-enthalpy fluid into a secondary, or booster, chamber for additional heat transfer. The MECH-X system has been shown to dissipate heat loads exceeding 10,000,000 W/m2 with dielectric fluid HFE7000 while maintaining surface temperatures below 95 °C.The present work reports on flow boiling experiments performed to characterize system-level performance of the MECH-X heat sink at mass fluxes of 680, 1440, and 3350 kg/s/m2. HFE7000 was used as a coolant at ambient lab temperature (∼23 °C) and a system pressure of 377 kPa. A 3.95 mm2 heating element, which simulated a heat generating component, was maintained below 95 °C with heats loads exceeding 1 kW/cm2. Experiments were terminated at this heat flux due to saturating a 50 VDC laboratory power supply. Results are also presented at a system pressure of 239 kPa, and results are compared to first generation PPF heat sinks.
       
  • Two-phase frictional pressure drop in a thin mixed-wettability
           microchannel
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): James M. Lewis, Yun Wang This study focuses on the experimental investigation of the two-phase pressure drop in a thin mixed-wettability microchannel. Air-water flows in a thin microchannel of dimensions 3.23 mm wide by 0.304 mm high. The test conditions primarily produce rivulet flow. The two-phase pressure drop increases when the base contact angle changes from 76° to 99°, with the other walls remaining the same. Combining the result with existing literature demonstrates that consistent behavior in the change of the two-phase pressure when comparing different wettabilities arises with careful consideration of the experimental parameters to classify experiments of adiabatic two-phase flow in a single microchannel into three categories: homogeneous, hydrophobic mixed-wettability, and superhydrophobic mixed-wettability microchannels. The two-phase pressure measurements also allow for the assessment of homogeneous, separated, and relative permeability models. Limiting the analysis to the rivulet flow regime allows for the determination of a new relative permeability exponent of 1.747 in the two-fluid model, which produces a mean absolute percent error of 14.9%. However, the models do not fully collapse the data, indicating differing air-water interactions. The work discusses possible causes of this behavior from experimental limitations to instabilities of the rivulet flow.
       
  • Heat flux reconstruction by inversion of experimental infrared temperature
           measurements – Application to the impact of a droplet in the film
           boiling regime
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): W. Chaze, O. Caballina, G. Castanet, J.-F. Pierson, F. Lemoine, D. Maillet An Inverse Heat Conduction Problem (IHCP) is considered in order to estimate the transient heat flux extracted from a hot solid surface by an impinging droplet. The resolution of the IHCP is made with the so-called quadrupole method, which provides an analytical expression of the temperature and the heat flux at the front surface of the solid wall, where the drop impact takes place. In the experiments, the thermal response of the front surface is recorded using IR thermography. For that, sapphire is chosen as the material of the solid wall, and the front surface is coated with a thin TiAlN ceramic layer (thickness of 300 nm). The latter is highly emissive and opaque in the IR while sapphire is transparent at the same wavelengths. This feature allows the surface impacted by the droplet to be viewed from the bottom by the IR camera. This approach has been implemented to gain some insights into the heat transfer from the solid surface as well as the formation and growth of the vapor film, which appears under the droplet in the regime of film boiling, when the solid temperature is much higher than the boiling temperature of the liquid. Due to the small thickness of the vapor film, heat conduction is predominant in the vapor layer. Hence, the thickness of the vapor film can be deduced from the value of the reconstructed local heat flux, assuming a linear profile of temperature between the liquid interface of the droplet at the saturation temperature and the solid surface measured by IR thermometry.Graphical abstractGraphical abstract for this article
       
  • Numerical analysis of droplet impact and heat transfer on an inclined wet
           surface
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Dashu Li, Xili Duan A numerical model based on the coupled level set and volume of fraction (CLSVOF) method is developed to investigate the dynamics and heat transfer of a droplet impacting on an inclined wet surface. Numerical results show that the droplet shows spreading, edge jets and splashing upon impact with high velocities. The front spreading factor and liquid velocity are larger than the back-spreading ones. As the impact velocity increases, both the front and back spreading factors and velocities increase. Significant air entrapment is observed when the droplet approaches the liquid film on the solid surface. The pressure difference between the trapped air and the liquids leads to the formation of an air film underneath the droplet. The entrapped air also shows a dynamic process. It becomes a small bubble at the initial stage of droplet impact and reduces heat transfer from the liquid droplet to the surface. This effect diminishes when the trapped air escapes the liquids. The average wall heat flux is found to be closely correlated to the impact velocity, but that correlation weakens as the impact velocity increases. Results from this study provide better understandings of the fluid dynamics and heat transfer during droplet oblique impact on inclined wet surfaces.
       
  • Experimental investigations on pressure oscillation induced by steam-air
           mixture gas sonic jets in subcooled water
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Weichao Li, Zhaoming Meng, Jianjun Wang, Jiaqing Liu, Zhongning Sun Present paper aims to experimentally investigate pressure oscillation induced by steam-air mixture gas sonic jets in subcooled water. Dynamic pressure signals and jet images are recorded and analyzed. Experimental results show that: the pressure oscillation dominant frequency decreases with the rise of water temperature, inlet pressure and air mass fraction. Air mass fraction has a complex effect on pressure oscillation intensity. When water temperature is less than 55 °C, as the air mass fraction increases, the pressure oscillation intensity increases first, and then decreases slightly, and then increases quickly. When water temperature is more than 55 °C, as the air mass fraction increases, the pressure oscillation intensity decreases first, and then increases quickly. The interfacial fluctuation height and pressure oscillation intensity dependency to the air mass fraction is the same near the nozzle exit. In addition, the validity of previous analysis model for steam sonic jet pressure oscillation dominant frequency is evaluated. A modified function considering the effect of air mass fraction is developed. The predicted results of steam-air mixture gas sonic jet pressure oscillation dominant frequency agree well with the experimental results. More than 98% of the data points are inside the error band of ±20%.
       
  • X-ray imaging analysis on behaviors of boiling bubbles in nanofluids
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Hanwook Park, Sang Joon Lee, Sung Yong Jung Nanofluid, a liquid suspension containing nanoparticles, has been widely used to enhance heat transfer. However, the heat transfer enhancement mechanism of nanofluids has not been clearly revealed yet. Therefore, understanding the boiling heat transfer of nanofluids is a challenging research issue in the field of heat transfer. When nanoparticles are added into a base fluid, the thermo-physical properties of the fluid and surface characteristics are modified. Those modifications induce changes in the behavior of boiling bubbles. In addition to the size and number of bubbles, the generating rate of boiling bubbles was newly defined to estimate the heat transfer coefficient directly from bubble behaviors according to nanofluid concentration. As the nanofluid concentration increases, both the generating rate of boiling bubbles and the heat transfer coefficient decrease. Wettability and hydrodynamic size were also employed to reason those degradations. Wettability increase leads to the reduction of activated nucleation sites, which reduces the bubble generating rate and heat transfer coefficient with an increase in nanofluid concentration. In this study, the feasibility and usefulness of synchrotron X-ray imaging and a newly defined boiling generating rate for examining boiling heat transfer were verified by observing boiling-bubble behaviors. Moreover, it was also shown that wettability plays an important role in changes of the bubble behaviors and the heat transfer coefficient as surface roughness modification.
       
  • Non-Oberbeck-Boussinesq effects due to large temperature differences in a
           differentially heated square cavity filled with air
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Qi Wang, Shu-Ning Xia, Rui Yan, De-Jun Sun, Zhen-Hua Wan We numerically investigate non-Oberbeck-Boussinesq (NOB) effects due to large temperature differences in a two-dimensional differentially heated square cavity using low-Mach-number equations. The working fluid is air and the Prandtl number Pr is 0.71 for the reference state. The considered Rayleigh numbers Ra range from 105 to 109. Various temperature differences ΔT̂ between the hot and cold plates are considered and the maximum value is up to 360K. The critical Rayleigh number for the onset of unsteadiness decrease with increasing temperature differences. The NOB effects on the temperature and velocity fields are investigated. It is found that both the thermal and velocity boundary layers become thicker near the hot plate while they get thinner near the cold plates under NOB conditions. The central temperature is increased compared to Oberbeck-Boussinesq (OB) cases considering NOB effects. The normalized center temperature θc roughly increases linearly with increasing temperature differential ∊. The horizontal velocity near the top plate is normally enhanced by NOB effects while it is normally decreased near the bottom plate under NOB conditions. In spite of these marked qualitative differences in the NOB flow relative to OB flow, the overall integral quantities like the Nusselt number Nu and Reynolds number Re are insensitive to NOB effects and retain their Ra-scaling exponents. The Nu has a minor decrease under NOB conditions. The maximum decrease is only about 3% for temperature difference as large as 360K. Within OB approximation, the Nusselt number Nu is found to scale as ∼Ra0.27, and the inverse thermal boundary layer thickness λθ-1 also scale as ∼Ra0.27. These scaling exponents do not change under NOB conditions. The Reynolds number based on the root mean square (r.m.s) velocity Rerms increases slightly for NOB cases. We also find Rerms∼Ra0.37,Rew∼Ra0.50,Rev∼Ra0.45 for OB cases, where Rew/Rev are Reynolds number based on maximum magnitude of vertical/horizontal...
       
  • Numerical modeling and experimental validation of fractional heat transfer
           induced by gas adsorption in heterogeneous coal matrix
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Jianhong Kang, Di Zhang, Fubao Zhou, Haijian Li, Tongqiang Xia Despite one fundamental issue in the adsorption theory of coalbed methane, little is known about the thermodynamic properties of gas adsorption in a porous coal matrix. In this work, considering the heterogeneity of pore structure and the exothermic characteristics of gas adsorption, a fractional heat conduction model with an unsteady volumetric heat source is proposed to study the heat transfer process induced by gas adsorption in a heterogeneous coal matrix. The heat conduction equation with a fractional time derivative is discretized by using an implicit numerical method based on the generalization of a standard finite-difference scheme. First, to validate the fractional heat conduction model, gas adsorption experiments on a microcalorimeter were carried out on 5 g coal samples of 0.3 mm diameter at 25 °C. The experimental heat flux with initial adsorption pressures of 3.23 bar, 5.83 bar and 9.77 bar increases rapidly from zero to peak values of 7.17 mW, 12.05 mW and 16.81 mW in less than 7 min (i.e., fast thermal diffusion stage) and then decreases slowly to zero again in approximately 2 h (i.e., slow thermal diffusion stage). It is revealed that for all tested gas pressures the fractional heat conduction model with a fractional order α=0.86 can reproduce the experimental process of heat flux with better accuracy than the Fourier law-based model (i.e., α=1), suggesting that anomalous thermal diffusion is the governing heat transfer process of gas adsorption in the coal matrix. Second, the spatial distribution and temporal evolution of temperature patterns with different model parameters are numerically simulated. It is found that the time to reach the peak temperature decreases from 760 s at the center of the coal particles to 490 s at the boundary. Finally, the parametric sensitivity of the thermodynamic properties of gas adsorption such as temperature, heat flux and integral adsorption heat is discussed in detail. Particularly, it is shown that as one of the most important thermodynamic parameters, the integral heat is very sensitive to the fractional order α. In the case of 3.23 bar, if α increases from0.75 to 1, while other model parameters remain unchanged, the integral heat could be enhanced from 1.1 J/g to 8.5 J/g.
       
  • Developing laminar natural convection of power law fluids in vertical open
           ended channel
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Enguang Zhou, Yildiz Bayazitoglu Steady, developing laminar natural convection heat transfer for power law fluids between two parallel vertical plates where the fluid is entrained from the bottom and exiting from top is studied. The results for asymmetric and symmetric configurations of the heated plates, which are kept at uniform temperatures with an aspect ratio of 40, are presented. For the numerical computations, the ANSYS Workbench Fluent commercial package is used to solve the governing equations and its numerical output is post-processed. Various range values of Rayleigh number (Ra = 104, 105, 106) Prandtl number (Pr = 10, 100, 1000), non-Newtonian power law indexes (0.6⩽n⩽1.4) of the fluids and the temperature ratios of colder and hotter walls (rT = 0, 0.5, 1.0) are considered. The temperature and velocity profiles, and the average Nusselt number distributions are presented. Comparisons between Newtonian and non-Newtonian fluids are made in terms of the variations of the average Nusselt number as a function of the non-dimensional governing parameters.
       
  • Water functionalized CuO nanoparticles filled in a partially heated
           trapezoidal cavity with inner heated obstacle: FEM approach
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Rizwan ul Haq, Sidra Aman This frame work is established to investigate the thermal management of free convection enclosed in trapezoidal cavity filled with the water based copper oxide (CuO) nanofluid. As nanoparticles volume fraction play a significant role to handle the thermal conductivity of any working fluid, so we have addressed the complex nature real world model that widely used at the industrial level and many other mechanisms. An identical trapezoidal shape cavity is placed inside the big trapezoidal cavity that have three various constraints at the surface (cold, insulated and heated). Since bottom wall of the outer cavity is partially heated so various heated portion tests are applied to analyze the influence of heat transfer within the entire cavity. Aspect ratio that depends upon the size of the inner cavity is also determine. Complete and compatible mathematical model is constructed in the form of nonlinear coupled partial differential equation. These set of equations are characterized under the law of conservation of mass, momentum and energy equation along with the restricted domain of the cavity. Koo and Kleinstreuer-Li (KKL) model is used for effective thermal conductivity and viscosity of the nanofluid. A Galerkin based Finite Element method (FEM) is implemented to attain the suitable results in term of stream function and isotherms within the restricted domain of the cavity. Results are also obtained for velocity and temperature of the nanofluid at vertically mean position of the cavity. The simulations are performed for nanoparticles volume fraction 0⩽ϕ⩽0.2 heated portion length 0⩽LT⩽1 aspect ratio 0.5⩽AR⩽3.0, Rayleigh number 104⩽Ra⩽105.7, and three heated conditions (cold, adiabatic and hot) for inner trapezium. It is found that flow and thermal field are getting stronger due to increase in Rayleigh number. However, fluid velocity is decreasing with increasing nanoparticles volume fraction ϕ as the fluid is getting dens. Heat transfer rate is decreasing with the increase in ϕ and LT due to dominant convection.Graphical abstractHeat transfer management of nanofluid at the inner and outer surface of the trapezium for various values for Rayleigh number.Graphical abstract for this article
       
  • Experimental research on the effective heating strategies for a phase
           change material based power battery module
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Youfu Lv, Xiaoqing Yang, Guoqing Zhang, Xinxi Li Constructing a complete battery thermal management (BTM) system consisting of both the heating and cooling functionalities is critical to guarantee the cycling life and safety of the power battery pack. In this work, we focus on the neglected issue of replenishing a cooling system with a heating functionality in a standardized power battery module. Two kinds of heating strategies, including forced air convection (FAC) heating and silicone plate (SP) heating are developed and then optimized on an advanced phase change material (PCM)-cooling based battery module. The experimental results show that the performance of the FAC heating strategies can be optimized by constructing a “close-ended” battery pack and increasing the fan number to recycle the waste heat and uniform the air flow field, respectively. The strategy of SP heating at 90 W demonstrates the most effective heating performance. For instance, an acceptable heating time of 632 s and a second lowest temperature difference of 3.55 °C can be obtained, resulting in a highest comprehensive evaluation factor of 0.42, much higher than those of other heating strategies (0.29–0.32). These encouraging results may raise concerns about constructing suitable cooling and heating functionalities simultaneously in a BTM system to realize a target oriented use, particularly those targeting various harsh operating environments.
       
  • The normal spectral emission characteristics of Ni-based alloys during
           oxidation at high temperatures
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Shunan Zhao, Xunfeng Li, Xiulan Huai, Xiaoming Zhou, Keyong Cheng The emissivity change due to oxidation of the Ni-based alloys that are used for turbine blades in severe environment will cause large errors in radiation thermometry. In this paper, the normal spectral emissivity of three Ni-based alloys DZ125, DD6 and K465 is experimentally measured during oxidation at about 810, 914 and 998 °C in air. And the measurement wavelength varies from 1.35 to 2.35 μm. The combined standard uncertainties of the normal spectral emissivity are less than 3%. The oscillations of the emissivity are observed, and the effects of oxidation temperature, heating time and wavelength on the emissivity are investigated. The oscillations of the emissivity are produced with growth of the oxidation film by the interference effect between the direct transmission radiation and the transmission radiation after reflections by the substrate and air/film interface emitted by of the substrate. The oscillation extremums of the emissivity shift towards larger wavelengths as the oxidation process proceeds. The results show that the normal spectral emissivity increases basically with increasing temperature and decreasing wavelength except for the occurrence of the oscillations of the emissivity. The normal spectral emissivity increases rapidly at the initial heating time, and the change of emissivity becomes slow when the oxidation tends to be saturated gradually. Furthermore, the emissivity models versus heating time and wavelength are established, which fit the experimental results very well. The relative errors of the fitting models for emissivity are less than 4%.
       
  • Elliptical double corrugated tubes for enhanced heat transfer
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Kristina Navickaitė, Luca Cattani, Christian R.H. Bahl, Kurt Engelbrecht The thermal performance at constant pumping power conditions was numerically investigated in ellipse and super ellipse-based double corrugated tubes. A significant increase in thermal efficiency in double corrugated tubes is accompanied with a reasonable penalty in flow reduction for the cases modelled. An ellipse and a super ellipse-based double corrugated tubes were modelled at laminar fully hydraulically developed incompressible flow. Each base geometry was analysed holding either hydraulic diameter constant or the cross-sectional area constant. The pressure drop was normalized to the length of each modelled tube in order to maintain the pumping power. Thermal analysis was conducted under constant wall temperature boundary condition. The governing equations for non-isothermal flow were solved using the finite element method, and the results of the simulations were normalized to an equivalent straight tube. Numerical results predict a thermal efficiency enhanced by 400% maintaining 4.2 times lower volumetric flow rate in double corrugated tubes at the same pressure drop. The global performance evaluation criterion increases up to 14% for the double corrugated tubes with an ellipse-base and up to 11% for the tubes with super ellipse-base.
       
  • New model for heat transfer calculation during film condensation inside
           pipes
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Yanan Camaraza-Medina, Abel Hernandez-Guerrero, J. Luis Luviano-Ortiz, Ken Mortensen-Carlson, Oscar Miguel Cruz-Fonticiella, Osvaldo Fidel García-Morales In this paper a new model is presented for heat transfer calculation during film condensation inside pipes. This new model has been verified by comparison with available experimental data of a total of 22 different fluids, including water, various refrigerants and organic substances, which condense inside horizontal, vertical and inclined tubes. The model is valid for a range of internal diameters ranging from 2 mm to 50 mm, reduced pressure values ranging from 0.0008 to 0.91, Pr values for the liquid portion of the condensate from 1 to 18, values of Reynolds number for the liquid portion between 68 and 84827, and for the portion of the steam between 900 and 594373, steam quality from 0.01 to 0.99 and mass flux rates in the ranges of 3–850 kg/(m2 s). The mean deviation found for the data analyzed for vertical and inclined tubes was 13.0%, while for the horizontal tube data the mean deviation was 11.8%. In all cases, the agreement of the proposed model for horizontal, vertical and inclined tubes is good enough to be considered satisfactory for practical design.
       
  • Image-based numerical prediction for effective thermal conductivity of
           heterogeneous materials: A quadtree based scaled boundary finite element
           method
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Yiqian He, Jie Guo, Haitian Yang Integrating advantages of the quadtree technique, the SBFEM, the image-based modelling approach, and inverse analysis, a new numerical technique is presented for the evaluation of Effective Thermal Conductivity (ETC) of heterogeneous materials. The quadtree technique provides a convenient way for mesh generation, and facilitates to image-based analysis. The inconvenience of hanging nodes caused in the quadtree mesh generation can be naturally avoided by SBFEM, consequently the temperature solutions of heterogeneous materials can be determined by the combination of quadtree technique and SBFEM, and are partially regarded as ‘experiments values’ for equivalent homogeneous materials. Utilizing a group of such ‘experiments’, the ETC can be obtained by solving a group of inverse heat transfer problems of parameters identification. Numerical examples are provided to demonstrate the effectiveness of the proposed approach, and the impacts of distributions and shapes of inclusions, and volume fractions are taken into account.
       
  • Forced convection heat transfer from a circular cylinder with a flexible
           fin
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Xu Sun, Zehua Ye, Jiajun Li, Kai Wen, Hui Tian Forced convection heat transfer from a circular cylinder with a flexible fin in laminar flow with Re = 200 and Pr = 0.7 is investigated numerically. The two-dimensional incompressible Navier-Stokes equations and energy equation are coupled with the Euler-Bernoulli beam equation to describe the flow-induced vibration (FIV) of the flexible fin considering the convection heat transfer process. The modified characteristic-based split scheme, Galerkin finite element method, semi-torsional spring analogy method and loosely coupled partitioned approach are employed irrespectively for the flow and convection heat transfer, fin vibration, mesh movement and fluid–structure interaction. The accuracy and stability of the proposed numerical method are validated using three benchmark models including the forced convection heat transfer from a stationary cylinder, forced convection heat transfer from a transversely oscillating cylinder and FIV of a flexible plate behind a square cylinder. Finally, forced convection heat transfer characteristics from a circular cylinder with a flexible fin with fin length l = 0.5D–1.5D (D is the cylinder diameter) and elastic modulus E = 104 - 5 × 105 are analyzed in detail. The numerical results show that, when the vortex shedding frequency approaches the natural frequency of the flexible fin, the FIV frequency is locked on the natural frequency and the fin exhibits large-amplitude vibration. As a result, the ‘dead water’ region behind the cylinder is reduced and the convection heat transfer is improved. In the combinations of parameters considered, a maximum of 11.07% enhancement in heat transfer is obtained by the flexible fin.
       
  • Influence of heating surface characteristics on flow boiling in a copper
           microchannel: Experimental investigation and assessment of correlations
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Prasanna Jayaramu, Sateesh Gedupudi, Sarit K. Das Experiments were carried out to investigate the effect of surface characteristics on flow boiling heat transfer and pressure drop in a microchannel using degasified and deionized water as the working fluid. Test section consists of a 40 mm long, 0.5 mm wide and 0.24 mm deep microchannel machined in copper. Experimental results are reported for three different surface characteristics – fresh machined surface (case-1), the same channel surface when aged after repeated experimentation (case-2) and the surface obtained after cleaning the same aged surface with 0.1 M hydrochloric acid (case-3). Parameters considered include inlet temperature 95 °C, mass flux from 1000 to 2220 kg/m2 s and heat flux from 400 to 1200 kW/m2. Single-phase experiments have been performed to estimate the heat loss from microchannel and also to validate the experimental setup. The results indicate that the boiling heat transfer performance of case-2 is lower than that of case-1 and the performance of case-3 is higher than that of case-1. The main reason behind the reduction of two-phase heat transfer coefficient for case-2 as compared to case-1 is attributed to the increased wettability due to the thermal oxidation of the heating surface caused by the repeated experimentation. The enhanced boiling performance of case-3 is attributed to the increased nucleation site density. However, the change in the two-phase pressure drop is relatively small. The experimental results were compared with the available correlations in the literature to check the predictability of the correlations for the three cases. The degree of agreement (or disagreement) varies depending on the correlation and the surface characteristic. The reasons for the deviations are discussed.
       
  • Heat transfer of laminar pulsating flow in a rectangular channel
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): R. Blythman, T. Persoons, N. Jeffers, D.B. Murray Pulsating flow has been found to both enhance and reduce heat transfer, although the explicit conditions that deliver heat transfer enhancement have yet to be identified. The current work builds on experimental and theoretical hydrodynamic analyses of earlier studies to investigate the effect of flow rate pulsations on the driving temperature difference for the case of constant heat flux, using a novel analytical solution to the energy equation in a rectangular channel. It is found that the oscillating temperature profiles are formed primarily as a result of fluid displacement against the temperature gradient, although diffusion at low frequencies and low Prandtl numbers obscures the mechanism. The temperature gradient at the wall is fixed for the case of constant heat flux, despite enhanced velocity gradients at the wall. The overall time-averaged change in Nusselt number with respect to steady flow is universally negative due to an enhanced axial heat flow towards the channel entrance, in agreement with similar studies in pipes. However, analysis of the time-dependent bulk temperature predicts that heat transfer is enhanced over the second half-cycle, where the flow rate is below it’s mean value. Hence, future work should investigate heat transfer enhancement using truncated sinusoidal flow rates.
       
  • Experimental study of saturated pool boiling heat transfer with FeCrAl-
           and Cr-layered vertical tubes under atmospheric pressure
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Hong Hyun Son, Yun Sik Cho, Sung Joong Kim This study compares the nucleate boiling heat transfer coefficient (NBHTC) and critical heat flux (CHF) of two candidate coatings, FeCrAl and Cr, being considered for accident-tolerant fuel (ATF) cladding applications. To form an intrinsic surface roughness, the tube surfaces were initially grinded with 800 and 60 grit sandpapers, and then, FeCrAl and Cr were physically deposited using the direct current magnetron sputtering technique. The FeCrAl- and Cr-layered surfaces became hydrophilic on the lumped nanostructures and superhydrophilic on the particulate nanostructures, respectively. When subjected to the pool boiling conditions of vertically-oriented tubes, the NBHTC and CHF of the FeCrAl-layered tube increased by 24% and 34%, respectively, with the exception of the similar NBHTC generated by the 60 grit sandpaper. In contrast, the NBHTC of the Cr-layered tube decreased by 15% due to the suppressed nucleation on the particulate nanostructures, while CHF increased by 27%. The CHF enhancement was analyzed based on the liquid spreading behavior of a water droplet from the morphological changes. The capillary flow rate, which is a product of the liquid spreading rate, us, and arithmetic roughness height, Ra, resulted in a more accurate prediction of the CHF than the equilibrium contact angle. Additionally, the potential boiling performance of the FeCrAl and Cr coatings were discussed by comparing the pool boiling results of the vertical tube and horizontal plate orientations.
       
  • Local heat transfer characteristics of natural circulation flow inside an
           8 × 8 partial spent fuel assembly under dry storage
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Doyoung Shin, Jae-Sung Kwon, Taeseok Kim, Sung Joong Kim The dry storage system has received immense attention for its safe and passive cooling mechanism as a method for managing highly radioactive spent fuels that inevitably result while using nuclear power. In order to ensure the integrity of the spent fuel cladding, it is important to accurately predict heat transfer characteristics inside the system. In the study, we investigated local flow field and heat transfer characteristics of natural circulation flow at a sub-channel scale inside a downscaled dry storage system. Natural circulation flow was generated with an 8 × 8 rod bundle heaters at a power level equivalent to the decay heat of the spent fuels. The temperature and flow field were measured with thermocouples and the non-intrusive particle image velocimetry (PIV) technique by assuming axisymmetry, respectively. The results indicated that the flow at the upstream of the spacer grid rapidly accelerated at a short distance prior to entering the spacer grid due to blockage effect of a spacer grid. At the downstream, the accelerated flow is discharged as a form of jet and slowly recovers its original velocity with respect to a relatively longer decelerating region. Heat transfer characteristics inside the sub-channels were elucidated by analyzing both flow field and temperature measurements. Empirical correlations for local Nusselt number were derived by using a combination of local Grashof and local Reynolds number. The correlations indicate a clear relation between local flow field and heat transfer characteristics. The flow acceleration caused by the blockage effect of the spacer grid intensified the forced convective effect that increased the local heat transfer rate.
       
  • Investigation of wave interference effect in Si/Ge superlattices with
           interfering Monte Carlo method
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Jincai Yu, Qi Li, Wenjing Ye The recently proposed Interference Monte Carlo (IMC) method is a mesoscale particle simulation method that is capable of modeling wave interference effect in addition to phonons’ particle behavior. Using the IMC, wave interference effect, which leads to a linear increase in thermal conductivity as the number of periods of superlattices increases, has been confirmed in Si/Heavy Si superlattices. Such a trend was also experimentally observed in AlAs/GaAs superlattices and has been regarded as the evidence of the coherent phonon heat conduction. In this work, wave interference effect in 1D Si/Ge superlattices at 300 K is investigated using the IMC method. First, the IMC method is further improved and validated with Molecular Dynamics simulations. It is then used to compute thermal conductivities of both periodic and aperiodic Si/Ge superlattices with fixed period length but varied number of periods. It is found that the nearly linearly increasing trend is present in both cases. However, this increasing trend is not caused by the wave interference, but is rather caused by the ballistic transport of low-frequency phonons due to their high transmission rates. Hence for Si/Ge superlattices with an average period length of 20 nm, the wave interference effect plays an insignificant role even when the interfacial scatterings are perfectly specular.
       
  • Observation of the mechanism triggering critical heat flux in pool boiling
           of saturated water under atmospheric pressure
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Satbyoul Jung, Hyungdae Kim We observed the dynamics of dry patches underneath massive bubbles during the pool boiling of saturated water under atmospheric pressure, and measured the associated temperature distribution. We synchronized the observations both spatially and temporally using high-speed total reflection and infrared thermometry techniques. The observations presented in this paper provide evidence that the critical heat flux phenomenon is triggered during the rewetting of large dry patches with periphery temperatures that are much lower than minimum film boiling temperature, so-called Leidenfrost point. As the liquid meniscus advanced toward the dry patch, numerous secondary bubbles nucleated and impeded the flow of liquid toward the dry patch. This prevented the liquid from rewetting the dry patch. The key physical mechanism for triggering CHF is initiated when the line density of the secondary bubbles nucleating at the periphery of a shrinking dry patch underneath a departing mushroom bubble exceeds a critical value. These bubbles completely block the liquid inflow into the dry patch and prevent rewetting, eventually causing the dry patch to expand irreversibly. We used our experimental data to determine an empirical value of the critical line nucleation site density.
       
  • Influence of lubricant-mediated droplet coalescence on frosting delay on
           lubricant impregnated surfaces
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Donghyun Seo, Seungtae Oh, Byungyun Moon, Hyunsik Kim, Juhyok Kim, Choongyeop Lee, Youngsuk Nam Condensation frosting causes serious economic and safety problems in many industrial applications. Recently, lubricant-impregnated surfaces (LIS) have been attracting much interest with their excellent anti-frosting ability. The facilitated removal of drops due to the low contact angle hysteresis of LIS has been suggested as the frosting suppression mechanism. Here, we demonstrate a hitherto-unexplored microscale frosting suppression mechanism on LIS by investigating microscopic condensation and freezing dynamics on LIS by varying the viscosities of the lubricants. Based on the ice propagation model, we show that the frosting propagation is suppressed on LIS with a low viscosity oil where the coalescence of droplets is promoted by the presence of oil. On the contrary, the coalescence between droplets is interrupted on LIS with a high viscosity oil, which facilitates the frost propagation. The criteria for the delay of condensation frosting were explained based on the competition between the lubricant drainage time and the drop growth time scale. Finally, we verify that microscopic frosting suppression mechanism of LIS persists up to macroscopic level by demonstrating that LIS is effective in suppressing condensation frosting on heat exchangers.
       
  • Theoretical and experimental studies of heat transfer characteristics of a
           single-phase natural circulation mini-loop with end heat exchangers
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Haojie Cheng, Haiyan Lei, Long Zeng, Chuanshan Dai In the present work, the heat transfer and fluid flow characteristics of a single-phase natural circulation loop (SPNCL) with both the heating and the cooling ends are theoretically and experimentally studied. Distilled water is chosen as the working fluid circulating in a rectangular loop that the top and bottom sides are respectively cooled and heated by 245 mm tube-in-tube heat exchangers. The height and diameter of the mini-loop are 250 mm and 4 mm, respectively. Both analytical and experimental results are obtained by varying the heating fluid temperatures from 30 °C to 60 °C but fixing cooling fluid temperature of 10 °C. Based on the experimental data, a Nu ∼ Re correlation is obtained and applied into the one-dimensional mathematical model. A good agreement between the experimental and theoretical results with a new correlation can be observed. Experimental results show that stable flow can be reached for the cases with different Th. The start-up time of natural circulation from quiescent state shortens with the increase of Th. The Reynolds number and heat transfer rate at steady state are proportional to the heating fluid temperature Th. Based on the proposed mathematical model, an optimal ratio of the heater length to the loop height can be reached when the total length and diameter of the mini-loop keep constants.
       
  • Determination of thermal conductivity of interfacial layer in nanofluids
           by equilibrium molecular dynamics simulation
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Xin Wang, Dengwei Jing In this article, equilibrium molecular dynamics are performed to investigate the thickness and thermal conductivity of interfacial layer around the nanoparticle in dilute nanofluids. A nanofluids system of a 1-nm-diameter copper spherical nanoparticle immersing into argon base liquids and then a flat interface formed by liquid argon on the solid copper surface are studied. Green-Kubo formula is developed to calculate thermal conductivity of interfacial layer. Besides, the effect of solid-liquid interaction is studied. The nano-scale thin interfacial layer with more ordered structure and higher thermal conductivity than that of the base fluids is observed. Then the simulation results are incorporated into the modified Maxwell equation to calculate the effective thermal conductivity of nanofluids. The results indicate that the contribution of interfacial layer to thermal conductivity enhancement of nanofluids can be neglected.
       
  • Topology optimization of the wick geometry in a flat plate heat pipe
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): S.A. Lurie, L.N. Rabinskiy, Y.O. Solyaev In the present study, a topology optimization approach is proposed to determine an optimal geometry of a wick sintered inside a flat plate heat pipe. Total thickness of the heat pipe is assumed as fixed, and thus the task involves redistributing the wick material and selecting the internal shape of the vapor core to provide a minimum power dissipation in the liquid flow and minimum total pressure drop in the entire heat pipe. Constraints are used for the maximum volume of the wick and maximum allowable temperature of the heat pipe wall. With respect to the preliminary assessments, the simulations are realized based on simplified 2D steady state thermal and hydrodynamic models assuming constant temperature and laminar flow in the vapor core and Darcy’s law for the liquid flow through the porous wick. Optimization results are presented for rectangular flat heat pipes with different lengths and thicknesses. Optimal placement of the wick columns and grooves are obtained by using the proposed topology optimization scheme. The results indicate that the use of the wicks of optimal shape increases the operating performance of flat heat pipes and especially increases their heat transfer capability up to twice that of heat pipes with flat wicks of constant thickness.
       
  • Flow deflectors to release the negative defect of natural wind on large
           scale dry cooling tower
    • Abstract: Publication date: January 2019Source: International Journal of Heat and Mass Transfer, Volume 128Author(s): Tao Wu, Zhihua Ge, Lijun Yang, Xiaoze Du In order to reduce the unfavorable impacts of natural wind, the arc curved air flow deflectors were proposed to be settled around the natural draft dry cooling tower. Based on 2 × 600 MW indirect air cooling power generating units, the thermo-fluid models of the natural draft dry cooling tower coupled with condenser of turbine are developed, by which the cooling performances are investigated at natural wind speed ranged from 0 to 20 m/s. The numerical results with experimental validations illustrate the thermo-fluid performance distributions of different cooling sectors around the dry cooling tower. It can be obtained that in the presence of ambient natural wind, the proposed deflectors could extend the positive effects of natural wind, leading to the decrease of outlet temperature of circulating water and back pressure of turbine. Compared to the case without deflectors, the total air mass flow rate could be increases by 50.26%, the outlet temperature of circulating water could be decreased by 10.73 °C and the back pressure of turbine could be decreases by 7.33 kPa when the wind speed is 20 m/s. In the absence of wind, the changes of air mass flow rate, heat rejection, outlet water temperature and back pressure are all no more than 0.5% compared with that without the deflectors, implying almost no negative impacts of the proposed deflectors under various operating conditions. The natural wind direction has little influence on the performance of natural draft dry cooling tower with deflectors.
       
 
 
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