Accepted Manuscripts

J. Heat Transfer   doi: 10.1115/1.4036039
This work present a simple thinking based on material's electrical and thermal properties which permit to searchers in domain of manufacturing and characterization of thin and thick films in solid state to take appropriate experimental conditions before the execution. Treatment of heat equations based on the photothermal deflection (PTD) technique, using some approximations founded on the determination of the thermal conductivity and thermal diffusivity and the calculation of the thermal diffusion length and comparing it with thicknesses of the substrate and the film deposited on it which constitute the sample and using the Cahill's law; we arrive to highlight, necessary conditions that allow searchers to manufacture samples with high thermoelectric power. These conditions are based on the experimental objectives that aspire many modern researches such as materials with low thermal conductivity and high electrical conductivity and the relationship between them to obtain materials with high figure of merit.
Technical Brief  
Ichiro Kano and Naoki Okamoto
J. Heat Transfer   doi: 10.1115/1.4036040
Our previous studies on the critical heat flux (CHF) of pool boiling have shown that CHF greatly increases with the application of an electric field and that the wall temperature can be decreased to a level with the safe operation of the electrical devices by using a low contact angle with the boiling surface. To verify the earlier prediction model, we investigated CHF enhancement by changing the contact angle with the boiling surface and by the application of an electric field. A fluorinated dielectric liquid was selected as the working fluid. To allow the contact angle between the boiling surface and the dielectric liquid to be changed, the different materials (Cu, Cr, NiB, Sn) and an mixture of 5 and 1.5 micro meter diamond particles were used as a boiling surface. The CHFs at different contact angles were 95 %~125 % of that for a polished Cu surface. Upon application of a -5 kV/mm electric field to the diamond particle surface, CHF of 99 W/cm2 at a superheat of 33.5 K was obtained. Based on this experimental evidence, we normalized the CHF and contact angle using our previously developed hydrodynamic instability model and semi-empirical model. This procedure allows us to develop a general model that predicted CHF well, including the CHF for the DI water.
Jozef Cernecky, Zuzana Brodnianska, Przemysław Błasiak and Jan Koniar
J. Heat Transfer   doi: 10.1115/1.4036041
The paper deals with the research of temperature fields in the proximity of heated pipes arranged above each other in natural air convection. The holographic interferometry method was used for the visualization of temperature fields. The experiments were made for pipes having the diameter of 20 mm, length 200 mm at surface temperatures of 40°C, 50°C and 60°C, with the vertical arrangement of pipes as well as with the horizontal shift of their centers by 1/4D and 1/2D.Temperature profiles were determined from experimentally obtained images of temperature fields and the local parameters of heat transfer were calculated. Under the same marginal and geometric conditions, CFD simulations of temperature fields were performed as well, while the results (temperature fields, local and mean parameters of heat transfer) were also calculated for various distances between the pipe centers (1D, 2D and 3D). From the obtained experimental results and CFD simulation results, it is possible to observe the impact of the arrangement and spacing of pipes on heat transfer parameters. The achieved results imply the change in the spacing of pipes has a greater impact on heat transfer parameters in the bundle of heated pipes located above each other than a moderate horizontal shift of their centers.
Zhongyang Shen, Qi Jing, Yonghui Xie and Di Zhang
J. Heat Transfer   doi: 10.1115/1.4036035
Cooling technique in mini-scale heat sink is essential with the development of high power electronics such as electronic chip. As heat transfer techniques, jet impingement cooling and convective cooling by roughened surface are commonly adopted. To obtain good cooling efficiency, the cooling structure within the heat sink should be carefully designed. In the present study, mini-scale heat sink with feature size of 1~100 mm is set up. Arrangement of jet impingement and dimple/protrusion surface is designed as heat transfer augmentation approaches. The effect of dimple/protrusion configuration and depth to diameter ratio is discussed. From the result, the heat transfer coefficient h distribution of heat sink surface is demonstrated for each case. The pressure penalty due to the arrangement of roughened structure is evaluated. Also, thermal performance TP and performance evaluation plot are adopted as evaluations of cooling performance for each configuration. Comparing all cases, optimal cooling structure considering the energy saving performance is obtained for the mini-scale heat sink. Referencing the statistics, new insight has been provided for the design of cooling structure inside mini-scale heat sink.
TOPICS: Heat sinks, Cooling, Heat transfer, Pressure, Design, Impingement cooling, Performance evaluation, Electronics, Heat transfer coefficients, Statistics as topic
Saurabh Bhardwaj and Amaresh Dalal
J. Heat Transfer   doi: 10.1115/1.4036036
In the present study, the interfacial dynamics of displacement of three-dimensional spherical droplet on a rectangular microchannel wall considering wetting effects are studied. The twophase lattice Boltzmann Shan-Chen model is used to explore the physics. The main focus of this study is to analyse the effect of wettability, low viscosity ratio and capillary number on the displacement of spherical droplet subjected to gravitational force on flat as well as grooved surface of the channel wall. The hydrophobic and hydrophilic nature of wettabilities on wall surface are considered to study for viscosity ratio, M =1. The results are presented in the form of temporal evolution of wetted length and wetted area for combined viscosity ratios and wettability scenario. In the present study, it is observed that in dynamic droplet displacement, the viscosity ratio and capillary number play a significant role. It is found that as viscosity ratio increases, both the wetted area and the wetted length increase and decrease in the case of hydrophilic and hydrophobic wettable wall respectively. The groove area on the vertical wall tries to entrap fraction of droplet fluid in case of hydrophilic surface of the vertical wall whereas in hydrophobic case, droplet moves past the groove without entrapment.
TOPICS: Mesoscopic systems, Viscosity, Drops, Displacement, Microchannels, Lattice Boltzmann methods, Wetting, Fluids, Physics, Dynamics (Mechanics), Gravity (Force)
Laura Colla, Davide Ercole, Laura Fedele, Simone Mancin, Oronzio Manca and Sergio Bobbo
J. Heat Transfer   doi: 10.1115/1.4036017
The present work aims at investigating a new challenging use of Aluminum Oxide (Al2O3) nanoparticles to enhance the thermal properties (thermal conductivity, specific heat, and latent heat) of pure paraffin waxes to obtain a new class of Phase Change Materials (PCMs), the so-called nano-PCMs. The nano-PCMs were obtained by seeding 0.5 and 1.0 wt% of Al2O3 nanoparticles in two paraffin waxes having melting temperatures of 45 and 55 °C, respectively. The thermophysical properties such as specific heat, latent heat, and thermal conductivity were then measured to understand the effects of the nanoparticles on the thermal properties of both the solid and liquid PCMs. Furthermore, a numerical comparison between the use of the pure paraffin waxes and the nano-PCMs obtained in a typical electronics passive cooling device was developed and implemented. A numerical model is accomplished to simulate the heat transfer inside the cavity either with PCM or nano-PCM. Numerical simulations were carried out using the ANSYS-Fluent 15.0 code. Results in terms of solid and liquid phase fractions and temperatures and melting time were reported and discussed. They showed that the nano-PCMs determine a delay in the melting process with respect to the pure PCMs.
TOPICS: Phase change materials, Computer cooling, Waxes, Paraffin wax, Melting, Nanoparticles, Thermal properties, Thermal conductivity, Specific heat, Temperature, Computer simulation, Latent heat, Cavities, Delays, Electronics, Heat transfer, Cooling, Aluminum
Anil Kumar Verma, Prasenjit Rath and Swarup Kumar Mahapatra
J. Heat Transfer   doi: 10.1115/1.4036015
In the present study, a three layered skin tissue has been modelled to assess the heat transfer characteristics in laser skin tumor tissue interaction. A finite volume based two-dimensional numerical bioheat transfer model has put together to study the damage prediction of healthy tissues by considering both Fourier and non-Fourier law. The combination of the bioheat transfer equation with Fourier law, forms the parabolic equation (Pennes model) and with the non-Fourier heat conduction equation forms the hyperbolic equation (thermal wave model). In this article, the laser source is provided on the outer layer of the skin to destroy the undesired tumor cell exemplified as inhomogeneity (tumor) in the intermediate layer. Laser source of constant intensity has put on till it reaches the tumor killing criteria. The heat transport equation has been discretized by the finite volume method where the central difference scheme is adopted for discretizing the spatial derivative terms. An implicit scheme is used to treat the transient terms in the model. For few cases of the hyperbolic problems, certain limitation for a chosen implicit scheme has also been addressed in this article. The results are validated with the existing literature. The evaluated results are based on both the Fourier and the non-Fourier model, to predict the temperature distribution and thermal damage by ensuring irreversible thermal damage in the whole tumor region placed in dermis layer. Thermal damage of the healthy tissue is found to be more in the time scale of thermal wave model.
TOPICS: Waves, Skin, Tumors, Damage, Biological tissues, Lasers, Bioheat transfer, Temperature distribution, Heat conduction, Heat, Heat transfer, Finite volume methods, Transients (Dynamics)
Guest Editorial  
Zhuomin Zhang, Chun Yang and Robert D. Tzou
J. Heat Transfer   doi: 10.1115/1.4036016
The 5th ASME Micro/Nanoscale Heat and Mass Transfer Conference (MNHMT 2016) was held in Singapore, January 4 - 6, 2016. This is Part I of the special issue.
TOPICS: Heat, Mass transfer, Nanoscale phenomena
Xidong Zhang, Guiping Zhu, Yin Zhang, Hongyan Wang and Hulin Huang
J. Heat Transfer   doi: 10.1115/1.4036004
An incompressible electrically conducting viscous fluid flow influenced by a local external magnetic field may develop vortical structures and eventually instabilities similar to those observed in flows around bluff bodies(such as circular cylinder), denominated magnetic obstacle. The present investigation analyses numerically the three-dimensional flow and heat transfer around row of magnetic obstacles. The vortex structures of magnetic obstacles, heat transfer behaviors in the wake of magnetic obstacles and flow resistance are analyzed at different Reynolds numbers. It shows that the flow behind magnetic obstacles contains four different regimes: (1) one pair of magnetic vortices, (2) three pairs namely, magnetic, connecting, and attached vortices, (3) smaller vortex shedding from the in-between magnetic obstacles, i.e. quasi-static and (4) regular vortex shedding from the row of magnetic obstacles. Furthermore, downstream cross-stream mixing induced by the unstable wakes can enhance wall-heat transfer, and the maximum value of percentage heat transfer increment (HI) is equal to about 35%. In this case, the thermal performance factor is more than one.
TOPICS: Flow (Dynamics), Heat transfer, Reynolds number, Vortices, Wakes, Vortex shedding, Fluid dynamics, Circular cylinders, Magnetic fields, Heat
Technical Brief  
Ulrich Olivier Dangui-Mbani, Jize Sui, Liancun Zheng, Bandar Bin-Mohsin and Goong Chen
J. Heat Transfer   doi: 10.1115/1.4036005
In this paper, an innovative heat conduction model, the Fisher-KPP reaction and n-diffusion Cattaneo telegraph equation, is firstly proposed, which take the Cattaneo relaxation flux, Philip n-diffusion flux, the pth-order Fisher-KPP reaction are into account. Approximate analytical solutions are obtained by the Adomian decomposition method and presented graphically. Some interesting results for temporal temperature evolution are obtained. Results indicate that the temperature profiles decrease with increasing of relaxation parameter and power law exponent n, while decrease with decreasing of Fisher-KPP reaction parameter p. Moreover, the other influence of pertinent parameters on the heat transfer phenomena are also presented.
TOPICS: Diffusion (Physics), Relaxation (Physics), Temperature profiles, Heat transfer, Heat conduction, Temperature
Technical Brief  
M. Tadi
J. Heat Transfer   doi: 10.1115/1.4036006
This note is concerned with a new method for the solution of an elliptic Inverse Heat Conduction Problem (IHCP). It considers an elliptic system where no information is given at part of the boundary. The method is iterative in nature. Starting with an initial guess for the missing boundary condition, the algorithm obtains corrections to the assumed value at every iteration. The updating part of the algorithm is the new feature of the present algorithm. The algorithm shows good robustness to noise and can be used to obtain a good estimate of the unknown boundary condition. A number of numerical examples are used to show the applicability of the method.
TOPICS: Heat conduction, Algorithms, Boundary-value problems, Robustness, Noise (Sound)
Mas Irfan P. Hidayat, Bambang Ariwahjoedi, Setyamartana Parman and T. V. V. L. N. Rao
J. Heat Transfer   doi: 10.1115/1.4036003
This paper presents a new approach of meshless local B-spline based finite difference (FD) method for solving transient heat conduction problems in complex geometries with spatially non-homogeneous and time dependent heat sources. In the present method, any governing equations are discretized by B-spline approximation which is implemented in the spirit of FD technique using a local B-spline collocation scheme. The key aspect of the method is that any derivative is stated as neighbouring nodal values based on B-spline interpolants. The set of neighbouring nodes are allowed to be randomly distributed thus enhanced flexibility in the numerical simulation can be obtained. The method requires no mesh connectivity for either field variable approximation or integration, hence truly meshless. Time integration is performed by using the Galerkin implicit scheme. Several transient heat conduction problems with non-uniform and localized heat sources having potential relevance in industrial applications are examined to demonstrate the efficacy of the present approach. Comparison of the method results with solutions from other numerical methods in literature is given. Good agreement with reference numerical methods is obtained and the presented new meshless local method is shown to be simple and accurate.
TOPICS: Heat conduction, Heat, B-splines, Numerical analysis, Approximation, Transient heat transfer, Computer simulation
Hengyun Zhang and Zhaoqiang Wang
J. Heat Transfer   doi: 10.1115/1.4035997
A formulation of the unit cell model and the corresponding thermal performance analysis for the cross-flow heat exchanger is carried out, with the design goal of dissipating 175W from a high power electronic chip in a compact space. A liquid to liquid heat exchanger in cross-flow arrangement is preferred due to its compact size and high effectiveness. The unit cell model is formulated based on the volume averaging method to determine the heat transfer coefficient involving the two heat exchanging fluids and the solid. The various factors such as channel shape, channel edge length, channel size, and heat exchanger material can be examined based on the unit cell model. The obtained heat transfer coefficients are used for the estimation of the heat exchanger thermal performance based on the effectiveness-NTU correlation. To verify the model formulation, a full field heat and fluid flow over the cross-flow heat exchangers are investigated through numerical computation. The amount of heat exchanged from the numerical computation is extracted and compared with the predicted results from the unit cell model. A fairly good agreement is obtained between the two approaches. Based on the unit cell model, a cross heat exchanger of eight channel layers for the hot and cold fluids, 15 channels in each layer with channel diameter of 2 mm, is able to meet the design target.
TOPICS: Heat exchangers, Cross-flow, Heat, Fluids, Design, Computation, Heat transfer coefficients, Fluid dynamics, Shapes
Technical Brief  
Chengcheng Deng, Xiaoxiang Yu, Xiaoming Huang and Nuo Yang
J. Heat Transfer   doi: 10.1115/1.4035998
We proposed a new way to enhance interfacial thermal conductance (ITC) of SiC through the overlapped carbon nanotubes (CNTs) with intertube atoms. Non-equilibrium molecular dynamics method was used to study the ITC. The results show that the intertube atoms can significantly enhance the ITC. The dependence of ITC on both the temperature and the number of intertube atoms are shown. The mechanism is analyzed by calculating probability distributions of atomic forces and vibrational density of states. Our study may provide some guidance on enhancing the ITC of CNT-based composites.
TOPICS: Atoms, Thermal conductivity, Carbon nanotubes, Molecular dynamics methods, Statistical distributions, Composite materials, Equilibrium (Physics), Fundamental forces (Physics), Density, Temperature
Yongtong Li, Liang Gong, Minghai Xu and Yogendra Joshi
J. Heat Transfer   doi: 10.1115/1.4035999
The present study presents a concept of bi-porous metal foam heat sink applicable to electronic cooling. This heat sink has two metal foam layers arranged in parallel along the primary flow direction, with different metal foam thickness, porosity, and pore density. The forced convective heat transfer in bi-porous metal foam heat sinks is numerically investigated by employing the Forchheimer-Brinkman extended Darcy momentum equation, and local thermal non-equilibrium energy equation. The effects of geometrical and morphological parameters on thermal and hydraulic performance are discussed, and the heat transfer enhancement is analyzed. The thermal performance of bi-porous metal foam heat sink is compared with that of uniform metal foam heat sink. The results show that the thermal resistance of the bi-porous metal foam heat sink decreases with decrease of top layer metal foam porosity at a fixed bottom metal foam porosity of 0.9. It is seen that the bi-porous metal foam heat sink can outperform the uniform metal foam heat sink with a proper selection of foam geometrical and morphological parameters, which is attributed to the presence of high velocity gradient at the boundary layer that can enhance the convective heat transfer. The best observed thermal performance of bi-porous metal foam heat sink is achieved by employing 30PPI metal foam at the bottom layer, with 50PPI metal foam at the top layer with the both porosities of 0.9, and the optimal thickness of the bottom foam layer is about 1mm.
TOPICS: Heat sinks, Metal foams, Porosity, Convection, Thermal resistance, Computer cooling, Density, Momentum, Flow (Dynamics), Heat transfer, Equilibrium (Physics), Boundary layers
Long Li, Xiaodong Jia and Yongwen Liu
J. Heat Transfer   doi: 10.1115/1.4036001
Outlet boundary condition (OBC) and its numerical scheme are critical issues in computational fluid dynamics, which may influence the accuracy and numerical stability of the computation. They are still challenges in two-phase lattice Boltzmann (LB) method, especially when large density ratio is considered. Three common used OBC schemes: convection boundary condition (CBC), Neumann boundary condition (NBC), and extrapolation boundary condition (EBC), are applied to large density ratio LB models (single and double distribution functions models) in this paper. The computation becomes unstable with the existing OBC schemes. Modifications for three different OBCs with various numerical schemes are proposed to overcome aforementioned issues. Numerical tests on two-phase droplet flows in a channel are performed to investigate the performance of the modified OBC schemes. Results indicate the modified OBC schemes are extended to tackle large density ratio situations. It is found that based on the single distribution function LB model the modified NBC scheme may lead to interior disturbance, and computation may diverage when the density ratio is larger than 400. The modified EBC scheme gives better performance than the modified NBC scheme which eliminates the stability issues for the single distribution function model. However, both the modified EBC scheme and modified NBC scheme become unstable when double distribution functions LB model is adopted. The modified CBC schemes give good performance for both the single and double distribution functions LB models even the density ratio is enlarged to 1000. The modified CBC schemes show high accuracy and good numerical stability.
TOPICS: Density, Boundary-value problems, Lattice Boltzmann methods, Outflow, Computation, Numerical stability, Stability, Flow (Dynamics), Drops, Computational fluid dynamics, Convection
Y. Chai, X. H. Yang, M. Zhao, Z. Y. Chen, X. Z. Meng, L. W. Jin, Q. L. Zhang and W. J. Hu
J. Heat Transfer   doi: 10.1115/1.4036002
As a relatively new type of functional material, porous graphite foam exhibits unique thermal physical properties. It possesses the advantages of low density, high specific surface area and high bulk thermal conductivity, and could be used as the core component of compact, lightweight and efficient heat exchangers. Effective thermal conductivity serves one of the key thermophysical properties for foam-based heat exchangers. The complex three-dimensional topology and interstitial fluids affect significantly the heat conduction in the porous structure, reflecting a topologically based effective thermal conductivity. This paper presents a novel geometric model for representing the microstructure of graphite foams with simplifications and modifications made on the realistic pore structure, where the complex surfaces and tortuous ligaments was converted into a simplified geometry with cylindrical ligaments joined at cuboid nodes. The multiple-layer method was used to divide the proposed geometry into solvable areas and the series-parallel relation was used to derive the analytical model for the effective thermal conductivity. To explore the heat conduction mechanisms at pore scale, direct numerical simulation was also conducted on the realistic geometric model. Achieving good agreement with experimental data, the simplified geometric model is validated. The numerically simulated conductivities follow the simplified model prediction, favoring thermally that the two geometries are equivalent. It validates further that the simplified model is capable of reflecting the internal microstructure of graphite foam, which would benefit the understandings for the thermophysical mechanisms of pore-scaled heat conduction and microstructures of graphite foam.
TOPICS: Thermal conductivity, Graphite, Heat conduction, Geometry, Heat exchangers, Functional materials, Density, Fluids, Foams (Chemistry), Computer simulation, Topology
Jnana Ranjan Senapati, Sukanta Kumar Dash and Subhransu Roy
J. Heat Transfer   doi: 10.1115/1.4035968
Entropy generation due to natural convection has been computed for a wide range of Rayleigh number based on fin spacing, RaS in the entire laminar range 5 ≤ RaS ≤ 108, for diameter ratio, 2 ≤ D/d ≤ 5 for an isothermal horizontal cylinder fitted with vertical annular fins. Entropy generation in the tube-fin system is predominantly due to heat transfer rather than of fluid friction. The results demonstrate that the degree of irreversibility is higher in case of finned configuration when compared with unfinned one. With the deployment of a merit function combining the first and second laws of thermodynamics, we have tried to show the thermodynamic performance of finned cylinder with natural convection. So, we have defined the ratio (I/Q)finned/(I/Q)unfinned. The ratio (I/Q)finned/(I/Q)unfinned gets its minimum value at optimum fin spacing where heat transfer is maximum. A detailed view of the entropy generation around the finned cylinder has been shown for various S/d at a particular D/d and Rayleigh number, which explains the nature and reason of entropy production.
TOPICS: Natural convection, Cylinders, Fins, Entropy, Rayleigh number, Heat transfer, Viscosity, Laws of thermodynamics
Swastik Acharya and Sukanta K. Dash
J. Heat Transfer   doi: 10.1115/1.4035919
Numerical simulations have been conducted to study natural convection heat transfer from solid or hollow cylinders in the laminar range of Ra spanning from 10^4 to 10^8 for L/D in the range of 0.05 = L/D = 20. Interesting flow structures around the thin hollow cylinder have been observed for small and large L/D. It has been found that the average Nu for solid or hollow horizontal cylinders in air is marginally higher than when they are on ground for the entire range of L/D and Ra limited up to 10^7. Up to a Ra of 10^7 Nu for a solid cylinder in air is higher than that of Nu for a hollow cylinder in air but when Ra exceeds 10^7 Nu for a hollow cylinder is marginally higher than that of the solid cylinder until an L/D of 0.2. When, L/D rises beyond 0.2 the situation reveres causing Nu for a solid cylinder to be again higher than that of the hollow cylinder when suspended in air. A solid cylinder on ground has higher Nu compared to that of a hollow cylinder on ground up to a Ra of 10^6. However, for higher Ra of 10^8 a hollow cylinder on ground has higher Nu compared to that of a solid cylinder on ground until an L/D of 5 and after that the situation reverses again.
TOPICS: Heat transfer, Natural convection, Cylinders, Computer simulation, Flow (Dynamics)
Banafsheh Barabadi, Satish Kumar and Yogendra K. Joshi
J. Heat Transfer   doi: 10.1115/1.4035889
A major challenge in maintaining quality and reliability in today’s microelectronics chips comes from the ever increasing levels of integration in the device fabrication, as well as from the high current densities. Transient Joule heating in the on-chip interconnect metal lines with characteristic sizes of tens of nm, can lead to thermo-mechanical fatigue and failure due to the thermal expansion coefficient mismatch between different materials. Full field simulations of nearly a billion interconnects in a modern microprocessor are infeasible due to the grid size requirements. To prevent premature device failures, a rapid predictive capability for the thermal response of on-chip interconnects is essential. This work develops a two-dimensional (2D) transient heat conduction framework to analyze inhomogeneous domains, using a reduced order modeling approach based on Proper Orthogonal Decomposition (POD) and Galerkin projection. POD modes are generated by using a representative step function as the heat source. The model rapidly predicted the transient thermal behavior of the system for several cases, without generating any new observations, and using just a few POD modes.
TOPICS: Principal component analysis, Transient heat transfer, Transients (Dynamics), Failure, Engineering simulation, Modeling, Heating, Microelectronic devices, Thermal expansion, Fatigue, Heat, Metals, Manufacturing, Joules, Reliability, Simulation

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