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  • Thermal routing via near-field radiative heat transfer
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
    Jinlin Song; Lu Lu; Bowen Li; Bo Zhang; Run Hu; Xinping Zhou; Qiang Cheng

    The diffusive nature of heat flow lays a formidable obstacle for directional heat manipulation, not akin to the wave-governed electromagnetics that can be well controlled in intensity and direction. By modulating the near-field radiative heat transfer among graphene/SiC core-shell (GSCS) nanoparticles, we propose the concept of thermal routing to address the directional heat manipulation in a particular many-body setup. The graphene shell introduces a minor polarizability peak and remarkably modifies the localized surface resonance of the particle, which plays a significant role in the radiative heat transfer within the many-body system consisting of GSCS nanoparticles. Consequently, Fermi levels of graphene shells matching allows directional radiative heat flow, thus enabling thermal routing manifested by variant designated temperature distributions. The proposed thermal routing could be used to dynamically tune heat flow in integrated nano-objects for thermal manipulation, and also opens avenues for exploiting novel thermal functionalities via radiative heat transfer at the nanoscale.

    更新日期:2020-01-17
  • Optimization of laminar convective heat transfer of oil-in-water nanoemulsion fluids in a toroidal duct
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
    Fang Liu; Huahao Sun; Dongxiang Zhang; Qiang Chen; Jun Zhao; Liqiu Wang

    This study presents numerical simulations, back propagation artificial neural networks and genetic algorithms for optimizing laminar convective heat transfer of oil-in-water nanoemulsion fluids having non-Fourier heat conduction characteristics. Firstly, a numerical study has been conducted on laminar flow and forced convective heat transfer of oil-in-water nanoemulsion fluids in toroidal ducts using Eulerian-Lagrangian two-phase approach. New correlations of drag coefficient, effective thermal conductivity and effective viscosity were adopted to improve the accuracy of simulation. Numerical results show that convective heat transfer can be enhanced by oil nanodroplets with thermal conductivity lower than that of the base fluid. Then regression models and artificial neural network models were developed based on simulation results for predicting convective heat transfer performances of nanoemulsions, considering effects of cross-sectional aspect ratio, Reynolds number, oil nanodroplet diameter and concentration. Artificial neural network models can predict mean Nusselt number and pressure drop better than the regression model. Finally, genetic algorithms was used to optimize convective heat transfer of nanoemulsions considering droplet migration. It can be found that low cross-sectional aspect ratio of width to height is beneficial for thermal performance factor. For single-objective optimization, mean Nusselt number reaches the maximum 32.3 at aspect ratio of 0.9677 and thermal performance factor reaches the maximum 1.305 at aspect ratio of 0.3935 under certain conditions. Pareto optimal set was obtained for two-objective optimization. This study would be useful for the optimal design of convective heat transfer of emulsions in toroidal ducts.

    更新日期:2020-01-17
  • Numerical study of melting performance enhancement for PCM in an annular enclosure with internal-external fins and metal foams
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
    Chunrong Zhao; Michael Opolot; Ming Liu; Frank Bruno; Simone Mancin; Kamel Hooman

    Application of different heat transfer augmentation techniques, including the use of fins or foams, were investigated to enhance the melting rate of a solid phase change material within an annulus where the inner and outer pipes were subjected to constant wall temperature. The carbon fibre fins as well as three commonly-used foams (made of three different materials: nickel, aluminium and copper) were simulated. Firstly, keeping the total fin volume constant, the fin number density effect on the melting rate was investigated. After an optimal fin number density was obtained, three possible strategies (unequal length, uneven intervals and tree-shaped fins) were explored aimed at a more comprehensive understanding of the induced heat transfer enhancement. It was observed that with a fixed fin thickness and volume, the melting time is not a monotonic function of the fin number density and can be optimized. Comparing pure PCM melting, the use of optimized fin number reduced over 60% of melting time, while additional 8% and 4% further time reduction could be achieved by appropriately increasing lengths and decreasing intervals of bottom fins, respectively. The use of tree-like fins resulted in a longer melting time, comparing to that of longitudinal straight fins, which indicates it is not always a good option. Finally, the results, primarily the melting rates, were compared with those obtained through the use of metal foams with different metals. It was observed that the melting time of optimized strategy-1 is rather less than those of Cu and Al foams, and approximately 2200s shorter than that of Ni foams. These results indicate that the fins, if designed properly, can be as efficient as foams.

    更新日期:2020-01-17
  • A visualized study of enhanced steam condensation heat transfer on a honeycomb-like microporous superhydrophobic surface in the presence of a non-condensable gas
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
    Tian-Yu Zhang; Lin-Wei Mou; Jia-Yi Zhang; Li-Wu Fan; Jia-Qi Li

    Steam condensation is a ubiquitous phenomenon of phase change that can be encountered in various industrial applications. In practice, the presence of non-condensable gases (NCG) is often inevitable, which can severely deteriorate condensation heat transfer by accumulating in the vicinity of the condensing surface as an additional thermal resistance. In this work, steam condensation heat transfer on a honeycomb-like microporous superhydrophobic surface, which has already been shown to lead to stable coalescence-induced droplet jumping with high heat flux, was studied with NCG concentrations up to ~28%. The superhydrophobic surface, having a nominal pore diameter of ~20 μm, was prepared by a rapid, cost-effective and highly scalable electrodeposition method over the outer surface of thin copper tubes. Condensation experiments were conducted in a visualized vacuum chamber maintaining at a constant pressure of 9.5 kPa. Significant enhancements of condensation heat transfer at the various NCG concentrations were exhibited on such superhydrophobic surface over a wide range of subcooling up to ~35 K, due to the successful realization of droplet jumping in spite of the presence of NCG. The adsorption of NCG into the micropores was elucidated to be a partial reason for prohibition of condensate flooding at relatively high degrees of subcooling.

    更新日期:2020-01-17
  • A curved lattice Boltzmann boundary scheme for thermal convective flows with Neumann boundary condition
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
    Shi Tao; Ao Xu; Qing He; Baiman Chen; Frank G.F. Qin

    We propose a curved lattice Boltzmann boundary scheme for thermal convective flows with Neumann boundary condition. The distribution function at the fluid-solid intersection node is obtained to accomplish the interpolation of unknown temperature distribution function at the boundary point. Specifically, the distribution function is first extrapolated from the fluid point along the lattice link; and then, the one in the opposite direction is evaluated by the anti-bounce back rule with wall temperature, which can be further determined by the specified Neumann boundary condition at the fluid-solid interface. The advantage of our scheme is that the involved inter/extrapolations are completely link-based, resulting in a quite efficient implementation procedure. Furthermore, our scheme has second-order spatial accuracy, and we verified in four numerical examples where analytical solutions are available: the heat transfer in a channel with a sinusoidal temperature gradient, the thermal diffusion in an annulus, and the conjugate heat transfer for these two cases. To further validate our scheme for thermal convective flow problems with complex geometries, we simulate the natural convection in an annulus, the thermal flow past a cylinder, and the mixed convection in a lid-driven cavity with a circular enclosure. The simulation results are consistent with existing benchmark data obtained by other methods.

    更新日期:2020-01-17
  • A numerical investigation of radiation feedback in different regimes of opposed flow flame spread
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
    Subrata Bhattacharjee; Kenneth Dong

    Radiation has been found to play an important role in opposed-flow flame spread, especially in the low-velocity microgravity environment. To explore the various aspects of flame radiation, an existing comprehensive 2D computational model including gas and surface radiation as well as radiation feedback to the solid is utilized. The comprehensive radiation model is simplified into a number of sub-models: no radiation, gas losses, surface loss, uncoupled (gas and surface losses without feedback). The sub-models are evaluated over the kinetic, thermal, and radiative regimes for a thin PMMA fuel. The resulting spread rates, flame and vaporization temperatures, and flame structures are compared to the comprehensive fully coupled model. The computational results reveal that gas-to-surface feedback moderately enhances spread rate and may affect the critical burnout velocity but has little effect on flame and vaporization temperatures.

    更新日期:2020-01-17
  • Controlled bubble departure diameter on biphilic surfaces for enhanced pool boiling heat transfer performance
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
    Do Yeong Lim; In Cheol Bang

    To elucidate the boiling heat transfer on a biphilic surface, the bubble departure diameter and the bubble location were controlled through the variation of the size and pitch of hydrophobic patterns on the biphilic surface. We postulated that if the average bubble departure diameter can be reduced, both the critical heat flux (CHF) and heat transfer coefficient (HTC) can be enhanced owing to the reduced dry spot area and increased active bubble cycle. The bubble dynamics and boiling performance were evaluated by adjusting the hydrophobic pattern size and the pitch of the biphilic surface using a porous superhydrophobic material with high adhesion to vapor, 14.5% of CHF and 34.1% of HTC in S2P4N64 biphilic surface were enhanced over the bare surface. The bubble departure diameter decreased as the pattern size and pitch decreased, and the CHF was enhanced in inverse proportion to bubble departure diameter. This study indicates that the bubble departure diameter on biphilic surfaces can be controlled according to the intentions of the designer.

    更新日期:2020-01-17
  • The pool boiling heat transfer and critical vapor column coalescence mechanism of block-divided microstructured surfaces
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
    Zeyang Lei; Bin Liu; Pengzhuo Xu; Yonghai Zhang; Jinjia Wei

    In this paper, the pool boiling heat transfer performance of cylindrical microstructured surfaces that were fabricated using the dry etching technique was studied. The working fluid was FC-72, and the experimental conditions included four different liquid subcooling temperatures (0, 15, 25, and 35 K). The heated microstructured surfaces consist of smooth parts and circular micropillar blocks, which are classified as single-block type (MP-1), four-block type (MP-2), 16-block type (MP-3, MP-4, MP-5) or composite-block type (MP-6). The material that was used as the substrate was P doped silicon chip. The experimental results showed that the heat transfer coefficient (HTC) and the critical heat flux (CHF) of all of the microstructured surfaces are greatly enhanced compared with the smooth surface because the block divisions and blank area could effectively prevent vapor columns from coalescing. Among the microstructured surface types, surface MP-3 has the largest CHF with different subcooling, while its actual heat transfer area of microstructured surface is relatively small. Furthermore, the mechanism and behavior of vapor column coalescence under critical heat flux conditions were analyzed. The prediction of CHF by using the critical vapor column radius (rgc) was compared and analyzed with the experimental data. Finally, the critical metastability phenomenon was demonstrated, and its occurrence mechanism was explored and explained. The experimental results show that restricting the coalescence of the vapor column is an effective method to augment CHF, and a high CHF can be obtained even when the surface area enhancement ratio is relatively low.

    更新日期:2020-01-17
  • Scale-integrated simulation of coupled radiation and convection in metal foam layer under high-flux irradiation
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
    Xin-lin Xia; Zhen-huan Li; Chao Fan; Xiao-lei Li; Chuang Sun

    Coupled radiation-convection heat transfer inside a unit metal foam layer with high-flux irradiation is studied using improved scale-integrated simulation. It integrates the discrete-scale CFD simulation with that of continuum-scale via the multi-domain concept with thermal radiation effect considered. Conservations of mass flux and energy are satisfied on these specified subdomain interfaces, and a special defined transition zone with geometry-dependent functional quantities is introduced within the continuum-scale subdomain. This zone is adjacent to the discrete-scale subdomain which ensures a reasonable transition. Absorbed radiative fluxes and radiative heat transfer within the whole domain are calculated with Monte Carlo method and treated as heat sources. The problem under consideration has been investigated via the discrete-scale simulation, the continuum-scale simulation, and the scale-integrated simulation. The accurateness of scale-integrated simulation has been fully validated for predicting both flow field and heat transfer characteristics in comparison with the outcomes of discrete-scale simulation and other investigations. Deviations between the outcomes of continuum-scale simulation and discrete-scale simulation are found to be mainly caused by inconsistent local absorbed radiative heat fluxes distribution and impinging effect around the entry region. Up to 70% and 60% reduction of computation time and memory footprints are achieved when scale-integrated strategy is employed for the CFD simulation compared with the discrete-scale simulation. Meanwhile, the detailed fluctuated characteristics of the local concerned region and overall heat transfer performance can be precisely reflected. It may break up the computation limitations of the discrete-scale simulation in studying the energy transport process in foam based solar receiver applications.

    更新日期:2020-01-17
  • Investigation of wettability on performance of pulsating heat pipe
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
    Jiansheng Wang; Jinyuan Xie; Xueling Liu

    A three-dimensional closed-loop pulsating heat pipe (CLPHP), with different wettability and charged with deionized water is numerically investigated in present work. The thermal performance and bubble dynamics of CLPHP are obtained under the condition of various input heat loads. It's found that the performance of CLPHP is affected by both surface wettability and input heat load. Under lower input heat load, CLPHP with hydrophobic surface (including superhydrophobic surface) has lower thermal resistance than that with hydrophilic surface. Conversely, CLPHP with hydrophilic surface starts up earlier, and has better thermal performance under higher input heat load. Specially, compared with the CLPHP with superhydrophobic surface, the thermal resistance of CLPHP with superhydrophilic reduces by 10.8% under the input heat load of 20 W. Moreover, the reversal of flow direction is observed in CLPHP with hydrophobic surface, while the stable directional circulation is always maintained in CLPHP with hydrophilic surface. The results indicate that the difference between advancing and receding angles (dynamic contact angle hysteresis) leads to various capillary resistance. Furthermore, due to lower flow resistance and the effect of liquid film, CLPHP with hydrophilic surface can effectively raise the dry-out input heat load.

    更新日期:2020-01-17
  • 更新日期:2020-01-17
  • Effect of Görtler-like vortices of various intensity on heat transfer in supersonic compression corner flows
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-15
    P.V. Chuvakhov; V.N. Radchenko

    Experiments on heat transfer over Mach 8, 15° compression corner flow affected by Görtler-like reattachment vortices of controllable intensity are carried out in the shock wind tunnel UT-1 M (TsAGI). Experiments cover two Reynolds numbers Re∞,L=(1.75±0.08) × 105 and Re∞,L=(3.90±0.15) × 105 based on the sharp flat plate length at which the reattachment flow is close to laminar or beginning transitional, respectively. The effect of streamwise vortices of different intensity on spanwise variations of the heat flux and its spanwise-averaged level at the reattachment region is investigated. The intensity of the vortices is varied by accurate controlling the height of a spanwise rake of cylindrical pins (seeding elements) placed on the plate ahead of the separation bubble.

    更新日期:2020-01-15
  • Hot-spot thermal management by phase change materials enhanced by spatially graded metal meshes
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-15
    Lien Chin Wei; Jonathan A. Malen

    Graded mesh inserts that spatially enhance the thermal conductivity of phase change materials (PCM) are optimized to minimize the time averaged thermal resistance between the heat source and the melt-front, to improve heat dissipation rates for electronics. Conventionally, the low thermal conductivities of PCM are enhanced by incorporating spatially-homogeneous porous fillers with high thermal conductivities. We investigate the relative advantages of porous fillers that spatially distribute enhancements to thermal conductivity. An arbitrary polynomial form of the spatial variation is optimized based on a numerical solution to the heat diffusion equation, to enhance heat dissipation rates in one-dimensional spherical and cylindrical coordinates. The most desirable spatial distributions are non-linear, have higher thermal conductivity near to the hot-spot, and a positive second derivative with respect to the radial coordinate (i.e. concave-up). We demonstrate enhancements of heat dissipation rates for constant temperature hot-spots, or reductions in temperature for constant power hot-spots, by factors of 900% and 300% in spherical and cylindrical coordinates, relative to those achieved by uniform fillers of equivalent average volume fractions. Recent advances in additive manufacturing make metal meshes with spatially graded volume fraction realizable.

    更新日期:2020-01-15
  • Numerical treatment of nonlinear Fourier and Maxwell-Cattaneo-Vernotte heat transport equations
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-14
    R. Kovács; P. Rogolino

    The second law of thermodynamics is a useful and universal tool to derive the generalizations of the Fourier’s law. In many cases, only linear relations are considered between the thermodynamic fluxes and forces, i.e., the conduction coefficients are independent of the temperature. In the present paper, we investigate a particular nonlinearity in which the thermal conductivity depends on the temperature linearly. Also, that assumption is extended to the relaxation time, which appears in the hyperbolic generalization of Fourier’s law, namely the Maxwell-Cattaneo-Vernotte (MCV) equation. Although such nonlinearity in the Fourier heat equation is well-known in the literature, its extension onto the MCV equation is rarely applied. Since these nonlinearities have significance from an experimental point of view, an efficient way is needed to solve the system of partial differential equations. In the following, we present a numerical method that is first developed for linear generalized heat equations. The related stability conditions are also discussed.

    更新日期:2020-01-14
  • The effect of interfacial mass transfer of slip-rising gas bubbles on two-phase flow in the vertical wellbore/pipeline
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-14
    Hongwei Yang; Jun Li; Gonghui Liu; Xing Xing; Hailong Jiang; Chao Wang

    During drilling or oil recovery, it is common that the formation trap gas invades the vertical wellbore/pipeline to cause the gas-liquid two-phase flow, which brings challenges and dangers to wellbore/pipeline pressure control. In this paper, coupling the interfacial mass transfer theory of slip-rising bubbles based on bubble hydraulics to the gas-liquid two-phase flow theory, a new transient non-isothermal gas-liquid two-phase flow model in the vertical wellbore/pipeline was developed. In this model, the effects of flow regime and heat transfer on the mass transfer rate were considered. The proposed model was validated using the measured experiment data and field data. Using this model, the effect of interfacial mass transfer of slip-rising bubbles on the evolution of gas-liquid two-phase flow in a special gas kick scenario was analyzed. The simulation results indicated that the mass transfer rate between oil dispersion and invasion gas was relatively slow, which made the gas not instantaneously dissolved in the oil dispersion or not instantly saturated the oil dispersion. Under the same gas invasion rate, the fraction and mass of free gas calculated by this model were always larger than those obtained by Yin's model, resulting in a faster of the bottomhole pressure reduction rate and pit gain increase rate. Additionally, increasing the gas concentration and flow rate could promote the interphase mass transfer rate, while increasing the temperature would inhibit it. This model could characterize the wellbore/pipeline gas-liquid two-phase flow with interphase mass transfer in more detail and accurately.

    更新日期:2020-01-14
  • Experimental investigation on stability, thermal conductivity and rheological properties of rGO/ethylene glycol based nanofluids
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-13
    Syed Nadeem Abbas Shah; Syed Shahabuddin; Mohd Faizul Mohd Sabri; Mohd Faiz Mohd Salleh; Mohamad Azlin Ali; Nasir Hayat; Nor Azwadi Che Sidik; Mahendran Samykano; R. Saidur
    更新日期:2020-01-14
  • Thermal contact conductance modeling of baring outer ring/bearing housing interface
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-11
    Chi Ma; Jialan Liu; Shilong Wang

    Currently, no model could be used to readily predict the TCR of baring outer ring/bearing housing interface, then a thermal contact conductance (TCC) model between cylindrical surfaces with transition fits is constructed. The topography is described by the fractal geometry to characterize the multiscale and self-affinity behaviors and two stochastic variables are introduced into the fractal function to guarantee the random and disordered features. Then the contact states of contact points are analyzed, and a new fractal inner contact model is established. An effective contact factor is introduced to modify the contact parameters. Eventually, the predictive model of TCCs is constructed by summing up the TCCs of all the contacting protrusions with different scales. To demonstrate the validity of the TCC model, the measuring setup of TCCs was developed, and then the tests were conducted. The results show that the average deviations between the measured data and predicted TCCs are 10.25% and 8.73% for SS304 and carbon steel, respectively. When the effective contact factor is not considered, the average deviations between the predicted TCCs and measured data are 25.47% and 20.61% for SS304 and carbon steel, respectively. Then the necessity to introduce the effective contact factor is verified. For SS304, the prediction accuracy of the present model is 15.22%, 56.36%, and 31.55% higher than that of the present model without effective contact factor, M-T model, and Zou model, respectively. For carbon steel, the prediction accuracy of the present model is 11.88%, 63.76%, and 34.87% higher than that of the present model without effective contact factor, M-T model, and Zou model, respectively. Finally, the effects of the surface roughness, the protrusion top radius, the effective contact factor, and the transition fit on TCC are discussed. The results show that TCC decreases with surface roughness. The TCC with different protrusion top radii is greater than that with identical top radius. The TCC increases with the effective contact factor slowly and then the growth rate increases rapidly. Besides, the TCC increases with transition fit sharply at the early stage, and then increases slowly for both SS304 and carbon steel.

    更新日期:2020-01-13
  • An elliptic numerical analysis of water vapour absorption into a falling film in vertical parallel plate channels
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-09
    Robabeh Abbasi Havestini; Scott J. Ormiston

    An implicitly coupled elliptic numerical model is applied to study the two-phase falling film absorption inside a parallel plate vertical channel. A complete set of two-phase two-dimensional governing equations are solved for co-current laminar flows of LiBr solution and water vapour. A precise liquid-gas interface is determined dynamically during solution over a non-orthogonal structured moving mesh. Fundamental interface boundary conditions are implemented to model the heat and mass interchange between the two phases. The capability of this new model is demonstrated through detailed comparisons with two previous parabolic and elliptic models. The impacts of the interface heat of absorption and mass fraction condition and the liquid film diffusion coefficient are investigated. New results are presented to examine the channel inlet pressure effect on the liquid film thickness development over the cold wall and the heat and mass transfer at the interface.

    更新日期:2020-01-11
  • High-frequency alternating nucleate boiling of water enabled by microslot arrays in microchannels
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-09
    Guanghan Huang; Wenming Li; Jiaxuan Ma; Congcong Ren; Chen Li

    Flow boiling in parallel and isolated microchannels has been extensively studied. In this study, five parallel microchannels (W = 200 µm, H = 250 µm, L = 10 mm) are interconnected by 28 micro-slots (20 µm wide and 250 µm deep) starting from the outlet. These micro-slots serve as nucleation sites to greatly enhance nucleate boiling. More importantly, the alternating and enhanced nucleate boiling in neighboring microchannels can generate additional pressure drop during the bubble growth-departure cycle and hence enable highly desirable periodic rewetting inside channels, particularly near outlet regions. This new microchannel configuration can substantially enhance nucleate boiling during flow boiling processes. Coupling with the enhanced nucleate boiling and the induced thin film evaporation, heat transfer coefficient (HTC) in present microchannel configuration can be enhanced up to ~107.6% at mass flux 250 kg/m2∙s with a ~17% higher critical heat flux (CHF) compared to the plain-wall microchannels with inlet restrictors (IRs). In addition, we achieve a CHF value of 810 W/cm2 at a moderate mass flux of 430 kg/m2∙s. All these enhancements are realized without compromising two-phase pressure drop compared to plain wall microchannels with inlet restrictors (IRs). Two-phase flow instabilities in terms of temperature and pressure drop fluctuations are also significantly suppressed.

    更新日期:2020-01-11
  • Detached eddy simulation of the flow field and heat transfer in cryogenic nitrogen jet
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-09
    Xiaoguang Wu; Zhongwei Huang; Xianwei Dai; John McLennan; Shikun Zhang; Ran Li

    Cryogenic nitrogen jetting is a promising drilling rate improvement method, in which heat transfer plays an important role in inducing thermal stresses and facilitating rock breakage. In the present study, we aim to study flow field and heat transfer of a cryogenic nitrogen jet in two potential phase states (i.e. liquid and supercritical) under downhole conditions and determine the effect of some critical engineering parameters, including inlet pressure, ambient pressure and standoff distance, which are of concern for field applications of this method. Three different detached eddy simulation (DES) approaches were compared and validated to assess their performances in jet flow issues. These comparisons indicate IDDES showed better performance in predicting the flow field and heat transfer of jet flow, and thus was adopted for the present simulations. According to the simulation results, vorticity, dominant frequency fd of vortex instability and pressure oscillations grow with increasing inlet pressure for both free and impinging jets. Compared to the liquid nitrogen (LN2) jet, the supercritical nitrogen (SCN2) jet has higher vorticity magnitude and fd of temperature fluctuations, causing its vortex rings to breakdown in advance. The dominant frequency of temperature oscillations at the stagnation point falls at the same level as that of vortex instability in the shear layer, revealing the prevailing role of large-scale vortices in heat transfer. Under the same jet pressure condition, the heat transfer rate for SCN2 jet is constantly higher than that of LN2 jet. Increasing inlet pressure helps increase fd of temperature fluctuations and heat transfer rate for both LN2 and SCN2 jets. Under the same pressure difference (between inlet and outlet), lower ambient pressure is more conducive for SCN2 jets to enhance the vortex scale and heat transfer rate. In contrast, the ambient pressure has no significant influence on the LN2 jet. In the range of h/d ≤ 6, higher standoff distance delays the transition of vortex structures in the wall jet zone and contributes to the enhancement of heat transfer efficiency.

    更新日期:2020-01-11
  • On flexible rectangular strip height on flat plate heat convection
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-09
    Yang Yang; David S-K. Ting; Steve Ray

    A 0.1 mm thick and 12.7 mm wide (W) rectangular flexible strip is experimentally investigated for its effectiveness in boosting the convective cooling from a heated flat plate in a wind tunnel. Three strip height, 25.4 mm, 38.1 mm and 50.8 mm, were explored at a 10 m/s wind, and a Reynolds number of 8500, based on the strip width. The heat transfer results are expressed in terms of Nusselt number normalized by the corresponding unperturbed reference case (Nu/Nuo). To uncover the physics behind the heat transfer enhancement, the turbulent flow characteristics were detailed via a 3D hotwire probe. The 25.4 mm-high strip generated vortex structures closest to the surface, and the largest near-surface-downwash velocity. These attributes result in a better mixing, and thus, heat removal. Therefore, the 25.4 mm-high strip provides the highest Nu/Nuo, with a peak value of approximately 1.76 at 9 W downstream, 0.26 larger than that of the 50.8 mm-high strip.

    更新日期:2020-01-11
  • Effective moisture diffusivity and drying simulation of walnuts under hot air
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-10
    Chang Chen; Chandrasekar Venkitasamy; Weipeng Zhang; Ragab Khir; Shrinivasa Upadhyaya; Zhongli Pan

    This study was conducted to determine the effective moisture diffusivity of walnuts for the understanding of drying mechanism and improved drying simulation. The drying characteristics of walnut shell and kernel were investigated during the single layer drying of in-shell walnuts at 43, 55, 65 and 75 °C with hot air. The values of average effective moisture diffusivity for walnut shell and kernel ranged from 1.51 × 10−9 to 9.28 × 10−9 m2/s and 1.13 × 10−9 to 2.85 × 10−9 m2/s, respectively. The 3rd order polynomial-exponential relationship well correlated the effective moisture diffusivity with sample moisture content (MC) and temperature (Radj2 > 0.983). A mathematical model with changing moisture diffusivity and heterogeneous components was developed. It simulated the in-shell walnut drying characteristics using finite element approach with good accuracy (Radj2 > 0.985). The outcomes provide important information for the understanding of moisture transfer mechanisms and have practical value for the optimization of operating conditions in the walnut drying industry.

    更新日期:2020-01-11
  • A DEM modeling of biomass fast pyrolysis in a double auger reactor
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-10
    Fenglei Qi; Mark Mba Wright

    Thermochemical conversion of biomass via fast pyrolysis is a proven pathway to product low-carbon crude bio-oils. In this research, an extended discrete element method (DEM) is proposed for simulating biomass fast pyrolysis reacting granular flows in a double auger reactor, in which particle hydrodynamics and interparticle heat transfer processes are involved and coupled with chemical reactions in solid particles. An adaptive time step algorithm is proposed to achieve a stable coupling between the integration of reaction ordinary differential equations and the DEM solver, and the algorithm is proven computationally efficient. A multi-component fast pyrolysis kinetics is adopted and its modeling accuracy is assessed by carrying out simulations of benchmark biomass pyrolysis experiments and comparing the prediction results with experimental data. The predicted product yields of bio-oil, char and non-condensable gas from the simulation of the biomass fast pyrolysis in the auger reactor are in satisfactory agreement with experimental measurements. The decomposition rates of biomass components in the reactor are revealed from the simulation and the pyrolysis number Py is calculated from the decomposition rate of biomass and the heat transfer coefficient. The Py number illustrates that the biomass fast pyrolysis process is limited by the heat transfer process at particle size of 2 mm.

    更新日期:2020-01-11
  • The formation of a cumulative jet during the collapse of a vapor bubble in a subcooled liquid formed as a result of laser heating
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-10
    V.M. Chudnovskii; A.A. Levin; V.I. Yusupov; M.A. Guzev; A.A. Chernov

    This paper presents the results of an experimental study of boiling of substantially subcooled liquid initiated by its local heating through the concentrated laser radiation transmitted to the working volume via a thin optical fiber. We study in detail the evolution of a vapor-gas bubble formed near the surface of an optical fiber tip. As the bubble collapses, a liquid seal is formed, which leads to generation of a hot submerged jet directed from the fiber tip into the liquid. We attempt to explain the cumulative nature of this jet and provide estimates of its velocity that appear to be in good agreement with the experiment.

    更新日期:2020-01-11
  • 更新日期:2020-01-11
  • A generalized model for calculating the thermal conductivity of freezing soils based on soil components and frost heave
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-10
    Jun Bi; Mingyi Zhang; Yuanming Lai; Wansheng Pei; Jianguo Lu; Zhilang You; Dongwei Li

    Thermal conductivity of freezing soils is an important parameter for the geotechnical engineering in cold regions. During a freezing process, unfrozen water freezes into ice. It changes soil components and induces frost heave, which will significantly increase the thermal conductivity of freezing soils. This study presents a generalized model for calculating the thermal conductivity of freezing soils with a consideration of soil components and frost heave. The generalized model for freezing soils was developed by different connections (e.g. series connection and parallel connection) between soil pores and solid grain and between unfrozen water and ice in the pores. This model was a function of unfrozen water content, frost heave, porosity, and initial water content. The proposed model was verified by measured data of eight silty clay samples with different dry densities and initial water contents. Results show that the calculated thermal conductivities agree well with measured data.

    更新日期:2020-01-11
  • Modeling of heat transport and exact analytical solutions in thin films with account for constant non-relativistic motion
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-10
    K. Zhukovsky; D. Oskolkov

    One-dimensional heat equations beyond Fourier law with account for non-relativistic motion of an observer with respect to the media are considered. Some analytical solutions to these heat transport equations are obtained. The effect of the motion of the observer in the media is studied. Heat transport in thin films is modelled by the system of inhomogeneous differential equations (DE), which involve Guyer–Krumhansl-type and Telegrapher's type equations. Analytical solution to this system is found for the initial Gaussian distribution in the case of Cauchy conditions and for zero initial heat flux. The comparative analysis of the obtained solutions is performed in wide range of Knudsen numbers, Kn⊂[0.1–1]. The effect of the relative media–observer speed on the perceived heat transport is explored.

    更新日期:2020-01-11
  • Influence of common simplifications on the drying of cement-based materials up to moderate temperatures
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-10
    Hani Cheikh Sleiman; Matthieu Briffaut; Stefano Dal Pont; Alessandro Tengattini; Bruno Huet

    The drying of cement-based materials affects directly their durability, which has a major financial/societal impact. Notably, the variation of saturation of the porous network as well as drying shrinkage are fundamental processes since they drive together cracking and the penetration rate of aggressive chemicals. Many macroscopic models describe the moisture transport within porous media. They can be broadly divided into two main categories: multiphase macro-models which take into account the presence of three fluid phases (liquid water, vapor and dry air), and simplified models considering less phases under the main assumption of constant gas pressure during the drying process. Moreover, the choice of different behavior laws, which describe different evolutions of desorption isotherms, relative permeability, permeability to liquid water in function of temperature, has a major impact on mass loss amount and kinetics. Quantification of these simplifications effects regarding the used model and the choice of behavior laws was done by comparing mass loss response surfaces in a relative humidity and temperature space for multiple configurations. The results show relative error maps at early, mid and late drying stages for every compared case.

    更新日期:2020-01-11
  • Active design for the tube insert of center-connected deflectors based on the principle of exergy destruction minimization
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-10
    J.Y. Lv; Z.C. Liu; W. Liu

    In this study, a circular tube inserted by center-connected deflector was proposed for heat transfer enhancement, and a numerical simulation with Re ranging from 300 to 1500 was conducted to analyze the thermo-hydraulic performance. The results indicated that the insert enhanced heat transfer with an acceptable increase of pressure drop by guiding the fluid from the core to boundary region and generating longitudinal swirl flow with multiple vortexes in the tube. The effects of Re and geometrical parameters including pitch (P), inclined angle (α) and deflector diameter (d) were analyzed. When compared to a smooth tube, the Nusselt number was increased by 2.51–9.46 times with the friction factor increasing to 2.48–10.77 times. The thermal dissipation was reduced by 4.82–10.56 times with power consumption increasing to 3.78–12.50 times. Efficiency evaluation coefficient (EEC) was in range of 0.92–1.56. Furthermore, a design method was proposed by applying the principle of exergy destruction minimization to determine the optimal geometric parameters of the insert, which was significant for the active design of the tube insert. The multi-objective optimization was performed by genetic algorithm along with artificial neural network. Thermal dissipation and power consumption ratios were chosen as optimization objectives. Then a compromised solution on the Pareto front was obtained. The result indicated that the EEC of the optimized structure (d = 3.63 mm, α = 35.85°, and P = 67.89 mm) was 1.32 and that the optimal result based on the principle of exergy destruction minimization had considerable overall performance.

    更新日期:2020-01-11
  • Investigation of current density spatial distribution in PEM fuel cells using a comprehensively validated multi-phase non-isothermal model
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-10
    Guobin Zhang; Jingtian Wu; Yun Wang; Yan Yin; Kui Jiao

    In this study, a three-dimensional (3D) multi-phase non-isothermal model of proton exchange membrane (PEM) fuel cell is present to investigate the current density spatial distributions under different output voltages, temperatures, current densities and relative humidities (RH). Two sets of experimental data are selected for validation, including those from the Los Alamos National Laboratory in the United States and the University of Waterloo in Canada. Reasonable agreements are achieved between the model prediction and experimental measurements, indicative of the validity of this 3D model. In addition, it is found that under a higher RH of 50%, most electric current is produced near the cathode inlet, which is primarily due to the local availability of abundant oxygen and hence small transport polarization. Low current occurs near the outlet of the cathode air flow, as a result of oxygen consumption by the oxygen reduction reaction (ORR). Under a lower RH of 25%, the high current density region shifts to the middle of the fuel cell, which is primarily attributed to hydration of the dry membrane by water production. In our case study, the operating temperature has little impact on the current density distribution.

    更新日期:2020-01-11
  • MD-based design of bilayer graphene-hBN heterostructures: An insight into enhanced thermal transport
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-10
    Fatemeh Momeni; Behzad Mehrafrooz; Abbas Montazeri; Ali Rajabpour

    The effective thermal properties, such as thermal conductivity, are of the most importance to explore the viability of using graphene-hBN van der Waals heterostuctures in nanoelectronic systems. Here, the thermal transport in hBN-graphene heterostructures has been investigated utilizing nonequilibrium molecular dynamics simulations. We observed that following the addition of hBN layer to the graphene, the thermal conductivity showed a rise up to ~ 25%. Moreover, to gain further insight into the role of shape and geometry of the hBN layer on the thermal conductivity of the heterostructure, five different arrangement patterns have also been taken into account. It was revealed that the ratio of hBN to graphene layer plays a more impressive role compared to the geometrical characteristics of the hBN layer.

    更新日期:2020-01-11
  • Thermal performance of curved-slope solar collector
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-09
    Xinping Zhou

    Sloped solar collector (SSC) is more efficient than horizontal solar collector due to its greenhouse effect and chimney effect driving the updraft. Large-scale SSC is proposed to be constructed on natural mountain slope to enhance the performance of solar chimney power generation. However, the surfaces of the natural mountain slopes always are not flat or even linearly rising but curving. In this paper, the thermal performance of curved-slope solar collector is studied based on two-segment slopes and compared with that of the linearly-rising-slope SSC. Results show that the optimal slope angle (OSA) of an SSC for reaching the maximum annual total solar radiation (ATSR) intensity is a little lower than the local latitude, and the maximum ATSR intensity is far higher than those on horizontal and vertical solar collectors. Furthermore, from a low point to a high point, the linearly rising slope (LRS) is the best for constructing solar collector compared to all the potential two-segment slopes. Furthermore, among the potential two-segment slopes, the slope of two closer slope angles is better. The conclusions are suitable for multi-segment slopes and curved slopes. This paper lays a solid foundation for location selection and design of SSC in future.

    更新日期:2020-01-11
  • The enhancement of spray cooling at very high initial temperature by using dextrose added water
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-10
    L. Das; A.R. Pati; Anita Panda; B. Munshi; D.K. Sahoo; K. Barik; S.S. Mohapatra; A. Sahoo

    In the current work, by decreasing the sensible heat extraction period and enhancing the internal energy of the evaporating droplet; the high mass flux spray cooling is enhanced with the additional advantages such as attainment of unaltered surface morphology and zero deposition of the additives on the evaporating surface. To achieve the above-mentioned requirements, dextrose is used as an additive in water, which decreases coolant temperature due to heat of dissolution. Furthermore, the exothermic reaction between aqueous glucose and oxygen fulfill the latter requirement. In the current work, the heat transfer analysis clearly depicts enhancement with respect to the heat removal rate obtained in case of cooling by pure water. In addition to the above, the post quenching surface analysis of the heat-treated steel plate assures unaltered surface morphology. The comparison of the current quenching process with the cooling processes reported in the literature clearly asserts its suitability for the fast quenching operation.

    更新日期:2020-01-11
  • Investigation on heat transfer in line chill-down process with various cryogenic fluids
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-08
    Lingxue Jin; Jisung Lee; Sangkwon Jeong

    This paper focuses on the transient process of the pipe cooling by the internal flow of cryogenic fluid, which is a so-called cryogenic line chill-down process. Due to the increasing use of cryogenic fluid in various industries, the heat transfer characteristics during the line chill-down process are followed with great interest. One of the biggest concern is that there are no universal heat transfer correlations for simulating the chill-down process. This research aims to extend the quenching database with liquid oxygen and predict the cryogenic line chill-down process with a one-dimensional homogeneous model. The line chill-down experiments are performed by liquid oxygen with the mass flux range from 15.9 kg/m2-s to 75.9 kg/m2-s. A 7 m long stainless steel 316 horizontal tube is used as the test section. The empirical correlations for heat transfer coefficient of single-phase vapor convection and film boiling are suggested based on the chill-down experimental data of liquid oxygen, liquid argon, and liquid nitrogen. The line chill-down process is simulated by applying the empirical correlations in a one-dimensional homogeneous model. The feasibility of the dynamic simulation model is verified in the mass flux up to 868 kg/m2-s by simulating the chill-down experimental data in the literature. Moreover, the characteristics of the critical heat flux, critical heat flux temperature, and minimum heat flux temperature are also investigated by comparing various experimental data and the empirical correlations. This study provides not only the open experimental data with liquid oxygen, which is rarely found in the literature but also the numerical simulation method, which predicts the line chill-down time within ± 10% error.

    更新日期:2020-01-09
  • Role of nanoscale roughness in the heat transfer characteristics of thin film evaporation
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-09
    Han Hu; Justin A. Weibel; Suresh V. Garimella
    更新日期:2020-01-09
  • A multiphase model for determination of minimum circulation ratio of natural circulation boiler for a wide range of pressure
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-09
    Md Naim Hossain; Koushik Ghosh; Nirmal K. Manna

    In the present work, in order to investigate and solve the issue associated with the circulation ratio (CR) for naturally assisted utility boilers, analysis of the boiler riser downcomer circuit has been performed for the whole range of operating pressure that supports natural circulation. This is done by developing a two phase flow model suitable for thermosyphon circuit analysis. The model is well validated with available numerical and experimental data for thermosyphon loop and practical boiler. In compliance with the industrial need, the tubes of boiler system are chosen based on the ASME boiler code. A set of case study of practical boilers has been conducted to determine the minimum possible safe circulation ratio for each separate case. Finally the computed circulation ratios are plotted against the operating pressure ranging from 5 to 180 bar. The trend of variation is discussed along with the discussion of safe operating range, considering the issue of vulnerability of tube overheating. The overheating of tube wall is correlated with the critical circulation ratio. The range of minimum safe CR is identified for low, medium and high operating pressure natural circulation boilers.

    更新日期:2020-01-09
  • Exact and approximate solutions of convective-radiative fins with temperature-dependent thermal conductivity using integral equation method
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-09
    Yong Huang; Xian-Fang Li

    The nonlinear thermal performance of convective and radiative longitudinal cooling fins with temperature-dependent thermal conductivity is studied. For linearly temperature-dependent thermal conductivity, the exact temperature distribution is obtained analytically in an implicit integral form. By converting the resulting integral equation to an algebraic equation, a simpler explicit expression of quadratic polynomials for the temperature excess in the whole convective-radiative fins is derived and the numerical results are compared with the exact one and the previous ones. Additionally, analytical expressions for the temperature change at the fin tip and for the fin efficiency are respectively given in terms of the thermal and geometric parameters of extended surfaces. The accuracy of approximate solution is examined. The influences of nonlinearity and hybrid Biot number on the temperature distribution, the fin-tip temperature change, and the fin efficiency are analyzed.

    更新日期:2020-01-09
  • Mixed dropwise-filmwise condensation heat transfer on biphilic surface
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-06
    Jian Xie; Qingting She; Jinliang Xu; Cong Liang; Wenxiao Li
    更新日期:2020-01-07
  • Numerical analysis of dominant parameters in synthetic impinging jet heat transfer process
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-06
    Ping Li; Xinyue Huang; Dingzhang Guo

    How forcing frequency of synthetic jet would affect heat transfer attracts wide attention, however, studies conducted by different authors or the same study but with slightly distinct conditions often led to disparate results. In regard to the forcing frequency-induced intricate phenomena in heat transfer process of synthetic jet, a mechanism analysis focusing on the effect of St is proposed in this work. In the present study, the emphases are to explore the effects of frequency (f = 10–75 Hz) and dimensionless parameters, i.e. Reynolds number (Re = 10,000–20,000) as well as Strouhal number (St = 0.1285–0.4498), on these physical processes of synthetic jet. The results demonstrate that there is an interval of St from 0.24 to 0.48 that corresponds to the highest range of time-area averaged Nusselt number under each Re. Moreover, Re or frequency would largely influence amplitude and variation trend of area averaged Nusselt number with normalized time respectively. However, interestingly, the variation trend of area averaged Nusselt number with respect to normalized time exhibits high similarity under the conditions of the same St even with different Re and frequency. Furthermore, the evolutions of flow field with normalized time are also analogous at the same St, which can lead to the similarity in the variation of heat transfer rate.

    更新日期:2020-01-07
  • Numerical modeling of YSZ droplet impact/spreading with solidification microstructure formation in plasma spraying
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-06
    Mingguang Shen; Ben Q. Li; Yu Bai

    A comprehensive numerical model has been developed, which is capable of representing the impact and spreading of a high-velocity yttria-stabilized zirconia (YSZ) molten droplet with microstructure formation in plasma thermal spraying processes. The numerical model entails the explicit finite difference solution of the Navier-Stokes equations and the energy balance equations, coupled with the Cahn-Hilliard equation to track the liquid-gas two phase interface and with a phase field model for solidification microstructure formation involving the polycrystalline growth. Numerical model procedures are given. The model, after being checked for mesh-independence, was applied to study the spreading and solidification of a high-temperature high-velocity YSZ droplet impinging upon a preheated substrate surface under the conditions typical of supersonic plasma thermal spraying processes. Extensive numerical simulations were carried out and results reveal that the solidification microstructure formed in the spreading droplet consists primarily of columnar grains. Computed results are also compared with thermal spray experiments, and gratifying agreement is obtained.

    更新日期:2020-01-07
  • An explicit expression of the empirical factor in a widely used phase change model
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-06
    Guang Chen; Taotao Nie; Xiaohong Yan

    Many boiling problems have been simulated by a phase change model (Lee model) involving an empirical mass transfer intensity factor. It is challenge to determine the value of this factor. An explicit expression of the mass transfer intensity factor is derived, and the accuracy of the expression is validated by comparing simulation results with theoretical solutions for two benchmark problems. The influences of various fluid properties (liquid phase density and thermal conductivity, latent heat, saturation temperature, vapor phase density and thermal conductivity) and mesh size on the mass transfer intensity factor are discussed. Results demonstrate that the mass transfer intensity factor depends on density and thermal conductivity of liquid phase, latent heat, saturation temperature and mesh size, but is independent of the density and thermal conductivity of vapor phase. Effects of vapor density and thermal conductivity on the phase interface movement are taken into account by the temperature of the interfacial cell. The expression reveals that a constant value of the mass transfer intensity factor throughout the computational domain is not reasonable, and which is the reason for divergence issue. In a specific computational cell, the value of the mass transfer intensity factor depends on the volume fraction of the liquid phase, and extremely large value of the factor should be consistent with extremely small volume fraction of the liquid phase.

    更新日期:2020-01-07
  • Enhanced cooling in compact helical tube cross-flow heat exchanger through higher area density and flow tortuosity
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-07
    Vandana Kumari Jha; Soubhik Kumar Bhaumik

    A novel configuration of compact cross-flow helical tube (CFHT) heat exchanger for cooling applications is proposed, in view of its inherent high surface area density and tortuous flow path. The cooling potential of such a configuration is assessed against that of its straight tube counterpart i.e., cross-flow straight tube (CFST) heat exchanger for similar volumetric air flow rates under laminar regime. Cross-flow experiments are conducted on CFST and CFHT unit systems for different helix angles ranging from 46∘ ≤ φ ≤ 72∘. CFHT exhibits superior cooling potential, with a manifold increase in heat extracted per unit volume of heat exchanger, as high as 1.5-3.3 times, and heat exchanger efficiency as high as 70% (for φ=72∘). The comparative assessment is extended to an array of (3 × 3) tubes in an inline arrangement, through CFD analysis, for a wider range of helix angles from 17∘ ≤ φ ≤ 72∘. Analysis reveals (i) flow intensification reflected in ~2.3 times increase in Re and (ii) 3D flow that eliminates dead zones otherwise observed behind the straight tubes. The flow features result in 1.4-2.5 times increase in Nu, 2-4 times increase in the rate of heat extracted and higher heat exchanger efficiency upto 90%. Thereby, the efficacy of CFHT heat exchanger in cooling applications is established.

    更新日期:2020-01-07
  • Metal alloy nanowire joining induced by femtosecond laser heating: A hybrid atomistic-continuum interpretation
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-06
    Yuanyuan Li; Yuting Li; Lanlan Feng; Gui Lu

    Nanojoining is a promising nano-fabrication technique with the capability of assembling functional nanodevices with dissimilar nanoscale and/or molecular components. However, significant challenges are encountered in experimental studies owing to the extremely small scale (10−9 m), high heating rates (1016 K s−1), and high temperature gradients (1011 K m−1) inherent in the nanojoining process. A hybrid atomistic-continuum model comprised of a molecular dynamics simulation (MD) and a two-temperature model (TTM) was used to study the mechanical and thermal characteristics of copper/copper-nickel alloy nanowires during a femtosecond laser nanojoining process. The results show that the laser nanojoining of two identical copper nanowires leads to the deterioration of thermal conductivity and thermal stress due to lattice structural variations. The nanojoining process induces an interface when applied to nanowires with different crystal orientations, which leads to phonon scattering at the joining interface, significantly reducing the thermal conductivity but providing for better mechanical properties. Additional alloy impurities strongly affect the thermal and mechanical properties during the laser nanojoining process. The thermal conductivity decreases significantly with increasing of nickel content while the mechanical properties are improved with respect to the Young's modulus and elastic limit. The utility of the hybrid MD-TTM simulations employed in the present work can approximate the laser nanojoining process in accordance with reasonable physical scenarios and accurate thermal and mechanical property predictions, which can also provide an atomic-level understanding of ultra-small, ultra-fast phenomena.

    更新日期:2020-01-07
  • A biosurfactant as prospective additive for pool boiling heat transfer enhancement
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-06
    Rinku Kumar Gouda; Manabendra Pathak; Mohd. Kaleem Khan

    Compared to chemical or synthetic surfactants, biosurfactants have been less explored in heat transfer applications. In the present work heat transfer performance of a biosurfactant (Rhamnolipid) solution in pool boiling experiments has been reported. Pool boiling experiments have been performed on a smooth copper surface with aqueous Rhamnolipid solutions at different concentrations and results have been compared with that of DI water. Surface tension and viscosity of newly developed surfactant solutions have been experimentally measured. Critical micelles concentration (CMC) of aqueous Rhamnolipid solution has been observed at 200 ppm. Significant enhancement of heat transfer coefficient is observed with Rhamnolipid solution at CMC value. It reports 200% enhancement in heat transfer coefficient compared to that with pure water. Active nucleation sites and less coalescence of growing of bubbles contribute for heat transfer enhancement in surfactant solutions. Like other surfactants critical heat flux (CHF) value of Rhamnolipid solution at CMC is observed less than that of pure water. However, reduction in CHF (23%) of present surfactant solution is less than the reduction in CHF (≈50%) of other surfactants. Present Rhamnolipids solution shows better heat transfer performance and higher CHF value compared to SDS surfactant. Moreover, it shows better heat transfer performance in comparison to other biodegradable surfactants reported in the literature.

    更新日期:2020-01-07
  • Parameter study on drag and heat reduction of a novel combinational spiked blunt body and rear opposing jet concept in hypersonic flows
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-06
    Jie Huang; Wei-Xing Yao

    A novel combinational configuration is proposed for drag and heat reduction in this paper, the CFD numerical method is adopted to study its drag and heat reduction performance. The results show that the aerodisk enhances the compression of hypersonic free stream by the spike to reduce the intensity of reattachment shock wave. The rear jet pushes the reattachment shock wave away from the blunt body and reduce the intensity of reattachment shock wave as well. In addition, the low-temperature gas from rear jet can also cool the blunt body directly. Increasing the length-diameter ratio of the spike reduces the intensity of reattachment shock wave, the rear jet gas can be ejected farther to push the reattachment shock wave father away from the blunt body. Increasing the diameter of aerodisk enhances the compression of hypersonic free stream to reduce the intensity of reattachment shock wave, while the shock wave drag of spike gradually increases. Therefore, with the increase of diameter of aerodisk, the total drag coefficient of combinational configuration first decreases and then increases. The rear jet presents the long penetration mode and short penetration mode. Increasing the total pressure ratio and the size of nozzle can push the reattachment shock wave away from the blunt body and reduce the intensity of reattachment shock wave, more low-temperature gas can also be injected into the flow field to cool the blunt body effectively. Finally, the flat disk has better drag and heat reduction performance than conical disk and hemispherical disk.

    更新日期:2020-01-07
  • Metal flow of weld pool and keyhole evolution in gas focusing plasma arc welding
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-07
    Tian Qing Li; Lu Chen; Yu Zhang; Xi Mou Yang; Yu Cheng Lei

    Establishing an open keyhole throughout work-piece is the key to penetrate work-piece fully in gas focusing plasma arc welding. In order to study heat transfer, metal flow and keyhole surface evolution in gas focusing plasma arc welding, the three dimensional mathematical model is developed. Arc heat model and plasma arc pressure model are used to describe heat and force action in gas focusing plasma arc welding. Temperature field, fluid flow in weld pool and keyhole evolution are simulated. It is found that metal in weld pool front flows bypass keyhole wall toward weld pool back. Center line of keyhole channel is crocked instead of going along z-axis. The calculated weld shape agrees with the experimental data basically. This work may enrich theoretical knowledge about the complicated thermal physical process and provide basic data to guide welding application in gas focusing plasma arc welding.

    更新日期:2020-01-07
  • Dynamic Leidenfrost temperature of saturated water drops on textured surfaces
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-06
    Junseok Park; Dong Eok Kim

    In this study, we propose an analytical model to predict dynamic Leidenfrost temperature for saturated water drops impacting on superheated smooth and textured surfaces. To define the Leidenfrost triggering mechanism, this model postulates a balance relation between the downward pressure by the drop itself and the resistant pressure arising from vaporization from the base of the drop; the former is expressed as the sum of dynamic and water hammer pressures induced by the drop motion while the latter is modeled with pressure buildup effect due to vapor flow within the thin film under the drop. The textured surfaces have uniformly distributed circular pillars with ~10 µm length scale, and the center-to-center pitch of the pillars varies from 15 to 120 µm. The experimental results show that the Leidenfrost temperature on textured surfaces increases at the same Weber number (We), as the pillar pitch becomes coarser. However, the Leidenfrost temperatures on the textured surfaces with relatively fine pitch were found to be rather lower than that on the smooth surface at the same We. Those experimental data are well predicted by the theoretical model, in which two simple equations with two unknowns (Leidenfrost temperature and thickness of thin vapor layer) are derived; one is based on the pressure balance relation and the other postulates an initial transient phase during drop impact.

    更新日期:2020-01-07
  • Heat transfer and friction of molten salt and supercritical CO2 flowing in an airfoil channel of a printed circuit heat exchanger
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-07
    Hong-Yuan Shi; Ming-Jia Li; Wen-Qi Wang; Yu Qiu; Wen-Quan Tao

    Airfoil printed circuit heat exchanger (PCHE) is considered as one of the competitive candidates in the 3rd generation of concentrating solar power (CSP) plant, where the molten salt and supercritical carbon dioxide (S-CO2) are adopted as the heat transfer fluids (HTFs). To study the flow features and heat transfer performance of the two HTFs in the airfoil channel of PCHE, a three-dimensional numerical model was firstly developed and validated by experiment. Then, the friction features and heat transfer of the two HTFs under different mass flow rate and inlet temperature conditions were numerically investigated. Then, the performance of distributed airfoil channels was compared with that of straight channels and zigzag channels. Finally, the heat transfer and friction factor correlations were fitted for the two HTFs in the airfoil channel of PCHE, which can be used in relatively wide ranges of Reynolds number and temperature. The results show that the larger inlet temperature leads to higher heat transfer performance for molten salt, but causes lower heat transfer performance for S-CO2. The airfoil channels have the best comprehensive heat transfer performance among these three channels at the given pumping power. Moreover, the maximum deviations between the simulation results and the proposed heat transfer correlations are within ±6% for both the molten salt and S-CO2. Finally, the maximum deviations between the proposed friction correlations and the calculated results are within ±4% and ±8% for the salt and S-CO2, respectively. The correlations and results given in current study can contribute to the design and application of airfoil PCHEs in the 3rd generation of CSP plant.

    更新日期:2020-01-07
  • Design optimization of an heat exchanger using Gaussian process
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-07
    Robin Campet; Pamphile T. Roy; Bénédicte Cuenot; Éléonore Riber; Jean-Christophe Jouhaud

    The objective of this work is to optimize the internal shape of a single-started helically ribbed heat exchanger. Large Eddy Simulation (LES) is used to simulate the turbulent flow in a wall-resolved periodic channel configuration, heated via a uniform heat flux at the wall. In order to enhance the heat exchange with the flow, the inner surface of the channel features rounded rib. This however increases the pressure loss, and an optimum shape of the rib is to be found. The rib pitch and height as well as rib discontinuities are the geometrical parameters to optimize, allowing a wide variety of inner wall roughness. To limit the number of LES, the optimization procedure is based on a surrogate model constructed from Gaussian Process Regression and adaptive resampling with the Efficient Global Optimization (EGO) method [1]. The optimization consists in the maximization of the cost function proposed by Webb and Eckert [2], which aims at maximizing the heat transfer efficiency for similar pumping power. Results show that a rib induced swirling motion in the near wall region significantly decreases the heat transfer efficiency, leading to an optimum roughness shape featuring large and multiple discontinuities. Moreover, the efficiency of helically dimpled tubes is also found sensitive to the shape of the transitions between the discontinuous parts of the rib. Smoother transitions lead to lower pressure loss but also to lower heat transfer due to smaller recirculation zones.

    更新日期:2020-01-07
  • Thermal conduction around a circular nanoinhomogeneity
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-07
    Kun Song; Peter Schiavone

    Taking interface phonon scattering into consideration, we present a set of thermal conduction interface conditions to simulate the interfacial temperature jump in nanocomposites and consequently obtain closed-form solutions describing thermal fields in the vicinity of a circular nanoinhomogeneity. Our results show that the heat flux inside the inhomogeneity is uniform and that the heat flux in the surrounding matrix can also be made uniform by designing the size or thermal conductivity of the inhomogeneity in the case when the thermal conductivity of the inhomogeneity is higher than that of the matrix. Using our theoretical results, we derive an explicit expression for the effective thermal conductivity of a rectangular region containing a circular nanoinhomogeneity. Furthermore, we undertake a numerical study to further explore the effects of interface phonon scattering on thermal conduction. Our results indicate that interface phonon scattering has the ability to suppress thermal conduction around a nanoinhomogeneity and has thus important applications in improving the performance of a range of functional materials.

    更新日期:2020-01-07
  • Magnetoplasmonic manipulation of nanoscale thermal radiation using twisted graphene gratings
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-07
    Ming-Jian He; Hong Qi; Ya-Tao Ren; Yi-Jun Zhao; Mauro Antezza

    In this paper, magnetoplasmonic manipulation of near-field radiative heat transfer (NFRHT) is realized using two twisted graphene gratings. As a result of the quantum Hall regime of magneto-optical graphene and the grating effect, three types of graphene surface plasmon polaritons (SPPs) modes are observed in the system: near-zero modes, high-frequency hyperbolic modes, and elliptic modes. The elliptic SPPs modes, which are caused by the combined effect of magnetic field and grating, are observed in the graphene grating system for the first time. In addition, the near-zero modes can be greatly enhanced by the combined effect grating and magnetic field, rendering graphene devices promising for thermal communication at ultra-low frequency. In particular, the near-zero modes result in a unique enhancement region of heat transfer, no matter for any twisted angle between gratings. The combined effect of grating and magnetic field is investigated simultaneously. By changing the strength of magnetic field, the positions and intensities of the modes can be modulated, and hence the NFRHT can be tuned accordingly, no matter for parallel or twisted graphene gratings. The magnetic field endows the grating action (graphene filling factors and twisted angles) with a higher modulation ability to modulate the NFRHT compared with zero-field. Moreover, the modulation ability of twist can be tuned by the magnetic field at different twisted angles. In sum, the combined effect of magnetic field and grating provides a tunable way to realize the energy modulation or multi-frequency thermal communications related to graphene devices.

    更新日期:2020-01-07
  • Diabatic visualization shows effects of micro-fins on evaporation of R410A: Smooth, axial micro-fin, and helical micro-fin tubes
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-06
    Cheng-Min Yang; Pega Hrnjak

    A novel approach to visualize the flow boiling inside a clear micro-fin tube under diabatic conditions is presented. Transparent smooth, axial micro-fin, and helical micro-fin tubes are made by 3D printing. The 3D printed tube is placed inside a glass tube and heated by the transparent secondary fluid flowing between the two tubes for providing the evaporation conditions and transparency. R410A flow boiling and the flow patterns in the three geometries captured with a high speed camera are compared. The experimental results show that micro-fin geometry influences flow behavior. Bubbles are mainly generated in the groove region due to a higher superheat than the fin region. Some of the liquid refrigerant is trapped in the grooves of the upper part of the micro-fin tube when the slug flow is present, and bubbles are generated in this thin liquid layer. In addition, the bubbles in the helical micro-fin tube are easier to merge because of the obstacle of the fin geometry for the bubble flowing path. As the two bubble merge, the conversion of surface free energy causes the bubble to travel with a higher velocity.

    更新日期:2020-01-06
  • Analysis of discharge channel characteristics based on plasma flow and heat transfer in USV-MF complex assisted WEDM-LS
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-06
    Yan Wang; Zong-Xue Li; Shun-Wen Yao; Cheng-Zhen Wu

    In this paper, the analysis of discharge channel characteristics from the view of plasma flow and heat transfer in ultrasonic vibration (USV) and magnetic field (MF) assisted low speed wire electrical discharging machine (WEDM-LS) process is proposed. According to the particle orbit theory, the motion equations of multi electrons are modified by Monte Carlo collision model. The study of discharge channel parameters reveals that the spatial shape of channel is changed and the length of channel path is increased when additional magnetic field is applied to the discharge machining, thus causing the channel current fluctuation. The simulation results of electrons motion process in magnetic field indicates that the time from cathode to anode increase by 15.38% and the diffusion of electrons reduce by 5%. The electron distribution on anode surface is relatively homogeneous after the completion of the discharge. The experimental results indicate that under the influence of magnetic field, the peak current in discharge channel increases obviously, the material removal rate (MRR) increases by 48.8% on average, and the number of micro cracks on machined surface decreases significantly.

    更新日期:2020-01-06
  • Relation between oxygen gas diffusivity and porous characteristics under capillary condensation of water in cathode catalyst layers of polymer electrolyte membrane fuel cells
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-06
    Toshihiro Kaneko; Yuta Yoshimoto; Takuma Hori; Shu Takagi; Junpei Ooyama; Takeshi Terao; Ikuya Kinefuchi
    更新日期:2020-01-06
  • An approach for multiple-fracture horizontal gas wells under a two-stage inner boundary condition
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-06
    Feng Tian; Xiaodong Wang

    Most wells are not produced under a single production condition in practice. Because the complexity caused by production condition changes is compounded, few studies have focused on wells under variable inner boundary conditions. This work proposes a semi-analytical model for multiple-fracture horizontal (MFH) gas wells under a two-stage inner boundary condition by applying source functions. The two-stage condition in this work represents the type of inner boundary condition change from the Dirichlet boundary condition to the Neumann boundary condition during production. An intermediate function is established to eliminate the effect whereby the initial pressure is not uniform. Pseudofunctions and Laplace transform are utilized to solve the model's mathematical problem. In addition, the accuracy of this model is fully verified by numerical examples. Finally, analysis of the characteristics of an MFH gas well under the two-stage condition is conducted. The results suggest that a low limiting pressure will lead to higher cumulative production. The initial rate mainly affects the production time and does not affect the final cumulative production. The initial rate should be adjusted based on the actual demand downstream and known fracture parameters, including the fracture half-length, fracture conductivity and fracture number. The limiting bottomhole pressure, initial rate and fracture parameters affect the formulation and optimization of the rational production allocation and production system for MFH wells. Moreover, combined with a variable-rate/pressure solution, this two-stage model can be expanded for more multistage production conditions. This work provides an approximation method for solving the nonlinear diffusivity gas equation under variable inner boundary conditions.

    更新日期:2020-01-06
  • Toward a multi-target multi-channel hyperthermia treatment system: Proof of concept with numerical simulations
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-03
    N. Nizam-Uddin; Wazie M. Abdulkawi; Ibrahim Elshafiey; Abdel-Fattah A. Sheta

    This paper presents electromagnetic therapy system based on a multi-channel approach for targeting multi-locous tumors, for hyperthermia treatment of the head region. This study aims to treat multi-lesions simultaneously. A numerical head phantom is developed to perform an electromagnetic simulation study to quantity specific absorption rate (SAR) accumulation at regions of interest to prove the efficacy of the proposed system. A custom monopole-based applicator array is designed and fabricated to project energy subcarriers of different frequencies toward the head phantom. A modified phase-array tool is invoked as waveform-shaping module to deposit energies coherently at tumor locations. The acquired SAR profiles are utilized to realize the thermal response of the case under study. The accomplished results prove the therapeutic capability of the proposed system by treating tumors of various sizes at different locations simultaneously, thereby adding a degree of freedom to improve the efficacy of hyperthermia treatment.

    更新日期:2020-01-04
  • Ekman boundary layer mass transfer mechanism of free sink vortex
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-03
    Dapeng Tan; Lin Li; Zichao Yin; Daifeng Li; Yinlong Zhu; Shuai Zheng

    The suction-extraction phenomenon occurs in the formation process of free sink vortex, and it is a complex gas-liquid coupling matter. The mass transfer mechanism of the Ekman boundary layer involved in the above matter is with important scientific value and engineering significance. To address the matters, we construct a Rankine-vortex-based fluid mechanic model, and propose a Helmholtz-equation-based solution method to acquire the critical penetration condition of sink vortex. The two-phase mass suction-extraction mechanism of the Ekman boundary layer is discussed. Then, a coupled computational fluid dynamic and discrete element method (CFD-DEM) modeling method is presented to obtain the matter transfer regularities of particles pumped by sink vortex, and the critical condition of particle stability motion is solved by the Laplace transform method. Numerical results show that the critical penetration condition is a data set because of different initial velocity components; the heights of suction/extraction holes form the container bottom have no relation to the initial velocity components; if the initial disturbances are enhanced, the suction-extraction height and Ekman layer thickness increase, but the Ekman suction-extraction intensities grow weaker; a particle aggregation phenomenon exists in the vortex center, and can be stable state until the surface tension broken by the Ekman suction effect, wherein the Ekman resultant force with different positions causes the particle motion trajectory to be complex. A PIV observation experimental platform is developed, and the effectiveness of the proposed method is verified. Then, the vortex core boundary is observed, so the radius of the vortex core can be acquired precisely; there is an energy transition process from potential energy to kinetic energy in the suction and extraction stages, which causes the Ekman boundary vorticity intensities to decline; the particle pumping process induces the aggregation and dissipation of turbulent vortices quickly, accelerating the fluid mass transfer efficiencies. The research works can provide direct guidance for the active control of vortex formation in industrial areas, and supply useful references to related fluids engineering calculation issues.

    更新日期:2020-01-04
  • Thermo-poroelasticity under constant fluid flux and localized heat source
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-03
    Xinle Zhai; Kamelia Atefi-Monfared

    Coupled thermo-hydraulic-mechanical behavior of saturated porous media with low permeability is of crucial significance to multiple operations including thermal treatment for declogging wellbores, thermal fracturing during production of unconventional shale oil, radioactive-waste disposal, and soft tissue and tumor growth. This work presents new thermo-poroelastic solutions for an isotropic medium subjected to a constant fluid flux and a localized heat source, incorporating two novel components: (a) transient flow transfer between the source and the embedding layer, thus incorporating the temporal thermo-poroelastic changes in the stress state adjacent to the source; and (b) vertical confinement effects on the mechanical response of the target zone, governed by the stiffness of the sealing media using the Winkler model approximation. The Westerly Granite is selected to assess the thermo-poroelastic alterations induced under the imposed fluid flux and heat loads. Results reveal generation of short-term thermal-induced pore pressures subsequent to injection initiation which otherwise cannot be predicted using current solutions. The new solutions capture higher thermal induced pore pressures and a more rapid dissipation under a higher heat transition rate between the source and the target zone. A compassion between the response of the porous layer under constant fluid flux and localized heat source, versus localized heat and flow sources reveals the former loading to be the most effective for localized thermal treatment as it results in: notably higher thermal-induced pore pressures, the maximum thermal-induced pressures to occur in the source vicinity; and particularly slower dissipation of the thermal-induced pore pressures. The stress paths demonstrate slight initial dilation before compaction under the latter loading; while the former results in an initial compaction with higher deviatoric stresses proceeded by dilation once the thermal-induced pore pressures tend to dissipate. Stress paths reveal the vertical confinement to remarkably impact the response of a porous layer. Higher compaction is generated under higher vertical confinement. In case of a mechanically free source-medium interface, lower vertical confinement gives rise to higher deviatoric stresses and lower mean stresses during the initial compaction phase, in addition to causing the formation to undergo dilation much sooner compared to when higher confinement is applied. For a mechanically fixed boundary setting, higher deviatoric stresses are generated under higher vertical confinements.

    更新日期:2020-01-04
  • Additively-manufactured metallic porous lattice heat exchangers for air-side heat transfer enhancement
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-03
    J.Y. Ho; K.C. Leong; T.N. Wong

    In this study, two novel porous lattice air-cooled heat exchangers (Lattice 1 and Lattice 2) were fabricated by the selective laser melting (SLM) technique from an aluminum alloy (AlSi10Mg) powder. Repetitions of the Rhombi-Octet unit cells of different cell sizes were used to form the porous matrices. Experiments were carried out in a wind tunnel to evaluate the thermal-hydraulic performances of the heat exchangers. The thermal performance indicators such as the overall thermal conductance (UA), air-side thermal resistance (Ra), air-side heat transfer coefficient (ha) and volumetric heat flux density (q˙v) of the porous lattice heat exchangers were determined and comparisons were made against two conventional fin-tube heat exchangers (Fin-tube 1 and Fin-tube 2). In addition, the pressure drops across the heat exchangers were also measured. Based on our investigations, it was determined that Lattice 1 exhibited approximately 40%–45% higher UA and ha than Lattice 2. However, the pressure drop across Lattice 1 was also higher than Lattice 2. At the same mass flow rate of air (m˙a), it was found that the ha values of the porous lattice heat exchangers were more than 2 times those of the fin-tube heat exchangers. The significantly higher ha values of the porous lattice are mainly attributed to the presence of interconnected pores and the formation of eddies downstream of the ligaments that improved fluid mixing. For the same pumping power (W˙/H), the use of the porous lattice heat exchangers also resulted in consistently higher ha values than the fin-tube heat exchangers. These results demonstrated the potential of using SLM to fabricate a new generation of commercial-scale compact heat exchangers made of porous lattices. These new porous lattice structures have enhanced the thermal performances of the heat exchanger with no penalty in pumping power.

    更新日期:2020-01-04
  • Numerical investigation of laminar flow and heat transfer in a liquid metal cooled mini-channel heat sink
    Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-02
    Adeel Muhammad; Deepak Selvakumar; Jian Wu

    With the recent trend of miniaturization and high-power output, effective heat dissipation has become the top priority in several industrial applications. This work contributes to the novel and efficient cooling technique that utilizes the liquid metal as working fluid. A numerical analysis of laminar flow and forced convective heat transfer of Galinstan through a mini-channel heat sink exposed to a constant heat flux has been presented. A detailed parametric analysis of the influence of heat sink's geometry, and the inlet velocity on the pressure drop, pumping power and the maximum heat flux has been carried out. Optimized heat sink's dimensions and inlet velocity are obtained. Furthermore, the numerical results are compared with the analytical correlations and discussion concerning the agreement and discrepancy is made. In addition, the flow and heat transfer performance of mini-channel heat sink cooling using liquid metal, nanofluid and water are compared, which intuitively shows the advantage of using liquid metal as coolant.

    更新日期:2020-01-02
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