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Abstract: Heat management is crucial to polymer electrolyte membrane (PEM) fuel cell commercialization. Numerical modeling is often used to simulate heat transfer in the various components of the cell and specifically the gas diffusion layer (GDL). Due to the porous nature of the gas diffusion layer and its complexity of anisotropy, the effect of the structure on the thermal conductivity is usually taken into account by introducing an effective thermal conductivity. In this study, the effective thermal conductivity of carbon paper diffusion media was estimated numerically. Carbon paper is often used as the GDL in PEM fuel cells due to its ability to efficiently transport electrons, heat and gaseous species. Using the GeoDict code, a realistic three-dimensional pore morphology of carbon paper was used as the modeling domain and the governing mathematical equations were solved using the commercial software package Fluent (6.3.26) and the ThermoDict solver. The geometrical effects on the effective thermal conductivity were investigated for different geometries. It was found that the effective thermal conductivity is highly sensitive to the geometry of the porous material under investigation. The effective thermal conductivity is much larger in the in-plane direction when compared with the value in the through-plane direction. Further, the change of the effective thermal conductivity due to porosity and compression was studied. Finally, correlations for the through-plane and in-plane effective thermal conductivity were developed. [Copyright &y& Elsevier]

Abstract: Effects of suction pressure and permeability on the steam heating characteristics of the wet paper are studied. Experimental results show that suction pressure enhances the energy absorption in the wet paper and effects of suction pressure strongly appear in the high-permeability paper, and also absorbed energy rate is decreased with increasing in heating time. From the numerical simulation results it is found that increase in moisture content and decrease of pressure gradient reduce the absorbed energy rate. Dimensionless numbers are derived from the basic equations to summarize the experimental and numerical simulation results. [Copyright &y& Elsevier]

Abstract: In a recent paper it is studied the steady natural convection heat transfer problem in a two-dimensional fluid-saturated porous medium embedded within a vertical annulus, whose inner and outer temperatures are uniform. Radiation heat transfer is taken into account, and the viscous dissipation effect is considered in the energy conservation equation. The present comment is related with two aspects of the paper, namely: (i) The radiation modeling of the problem, using the Rosseland approximation; and (ii) The energy formulation of the problem. [Copyright &y& Elsevier]

This paper provides a rudimentary insight into the influence of heat and mass transfer on the magneto-hydrodynamic (MHD) Jeffrey fluid peristaltic flow filling porous space in a symmetric inclined channel using a rotating frame with chemical reaction. In contrast to previous attempts, the flow formulation is based on the impact of a modified Darcy's law porous media on the Jeffrey fluid condition. The derived equations were solved analytically via the standard long wavelength and low Reynolds number assumptions to determine the pressure gradient, temperature, dimensionless velocity, pressure rise, and friction force. Otherwise, the concentration was numerically processed using the ND-Solve built-in command of Mathematica. Such a numerical technique is beneficial in minimizing error and reducing CPU time per evaluation. It chooses an appropriate algorithm for solving the problem. The graph is used to physically interpret the numerical answers for the base flow profiles. For numerous parameters of interest that enter into the issues, graphical findings are developed and tested. The impacts of various involved parameters appearing in the solutions are carefully analyzed. The trapping phenomena are discussed for several parameters. Electromagnetic peristaltic micropumps, for example, are one application of the current study in biomedical engineering. It was claimed that our systematic approach may constitute a basis for accurately examining the impact of heat and mass transfer on the magneto-hydrodynamic (MHD) Jeffrey fluid peristaltic flow filling porous space in a symmetric inclined channel using a rotating frame with chemical reaction, useful for diverse medical applications such as gastric fluid flow through the small intestine. [ABSTRACT FROM AUTHOR]

• A theoretical framework is proposed to consider non-equilibrium configurations at the macroscopic scale. • The new formulation is validated using a full dual-scale model of coupled heat and mass transfer. • With the new model, a very good accuracy is obtained with a huge reduction of CPU time. • Dual-scale diffusion and molecular relaxation can be considered additively in the modified macroscopic formulation. • This framework can be applied to other configurations, such as coupled transfer in packedbeds. This paper proposes a macroscopic formulation of coupled heat and mass transfer that can consider non-local equilibrium often encountered in biosourced building materials (wood- and plant-fiber based materials). Transferring dual-scale effects and molecular relaxation at the macroscopic level involves a kernel function acting in a convolution product. To ease the computational solution of the set of equations, the memory function is decomposed as a series of exponential functions. Each function yields an internal variable that obeys a simple ordinary differential equation (ODE). This paper first describes the macroscopic and dual-scale formulations used as reference solutions. Subsequently, the modified macroscopic formulation of coupled transfer and its computational solution are presented in detail. The major outcomes of the present study, validated against reference solutions obtained with a comprehensive dual-scale model, are as follows: • Dual-scale diffusion can be approached accurately by two exponential functions, • Even though the dual-scale phenomenon and molecular relaxation do not occur at the same scale, both can be considered in the modified macroscopic formulation of coupled transfer additively, • The new macroscopic formulation, together with the computational procedure proposed in this study, can be applied to various configurations, namely coupled heat and mass transfer in packed beds. [ABSTRACT FROM AUTHOR]

The deposits of corrosion products inside the PWR core (known as CRUD) will endanger the operational security of the reactor by mean of heat transfer and boron hideout. In this paper, a set of analytical method is proposed to simulate CRUD growth and heat transfer simultaneously of heater rod. CRUD growth involves a dynamic equilibrium of corrosion product deposition and deposits erosion to calculate the CRUD thickness. The CRUD interior heat transfer model evaluates the heat transfer mechanism based on the vapor-liquid-solid ratio within the porous media and calculates the overall heat resistance. The surface heat flux distribution model considers the bubble dynamic parameters in relation to the CRUD surface characteristics to determine the heat flux distribution. The comparison of predicted results with WALT experimental data yields a relative error within ±0.95 %, which indicates that the proposed method can precisely predict the alteration in thermal resistance during CRUD growth. As the thickness of CRUD increases, the heat transfer of the heater rod undergoes an initial enhancement and subsequent deterioration. Higher porosity results in lower cladding temperature, whereas a greater chimney area leads to higher cladding temperature. The wall heat flux has a positive correlation with the CRUD growth rate, while the flow rate and subcooling of the coolant inlet have an opposite tendency. [ABSTRACT FROM AUTHOR]

Non-Newtonian fluids such as asphalt are widely used in engineering field, but their application will also cause environmental pollution. This paper investigates the MHD flow of this kind of non-Newtonian fluid in porous media by using fractional Burgers' model. The effects of first-order chemical reaction, radiation effects and periodic oscillating boundary condition on fluid flow, heat and mass transfer are considered. The governing equations including a multi-term time fractional derivative are obtained by using the modified Darcy's law, fractional Fourier's law and fractional Fick's law. A convergent and stable L-algorithm, is established for governing equations. The influences of model parameters on the velocity, temperature and concentration distributions are analyzed. Numerical simulation results indicate that fractional derivative α and Darcy number Da have significant effect on velocity distribution. The momentum boundary layer becomes thinner remarkably with fractional derivative α. While the influence of Darcy number Da on the velocity performs conversely. [ABSTRACT FROM AUTHOR]

Highlights • Transport characteristics in porous media are reviewed, including flow and heat transfer. • Transport phenomena of nanofluids are comprehensively summarized, involving heat conduction, convection and radiation. • Transport literatures for the combination of nanofluid and porous medium are classified and concerned. • Phase change heat transfer of nanofluids and porous media are summarized for liquid-gas type and solid-liquid type. • This review involves conduction, convection, radiation and phase change for specified media. Abstract Increasing the heat transfer rate of heat transfer equipment is an ever-lasting topic in thermal engineering. Due to the advantages of light weight, high specific surface, high thermal conductivity, metal foam is a good extending surface for heat transfer enhancement. Nanofluid has a higher thermal conductivity than the traditional base fluid, so it can be used as an efficient heat transfer medium. This paper focuses on various flow and heat transfer modes of nanofluid, metal foam and the combination of the two, with the physical properties of nanofluid and metal foam summarized. The characteristics of flow and heat transfer are introduced. The motivation of this review paper is to arouse the researchers to pay attention to the basic transport understandings for the heat transfer enhancement of nanofluids in porous media. The knowledge reviewed in this paper is useful for improving the performance of compact heat exchangers, and heat sinks for cooling electronics with porous media and nanofluids. [ABSTRACT FROM AUTHOR]

In this paper, droplet impact on a porous surface is experimentally investigated over a wide range of Weber numbers and surface temperatures. Regime transition criteria have been deduced to determine droplet post-impingement behaviour as a function of the Weber number and surface temperature for which a droplet impacting on a porous surface. Based on the energy balance, an analytical model with improved boundary layer description is proposed to predict maximum spreading of droplet following impact on porous surfaces when the effect of heat transfer is negligible. The results of the model indicate that the spreading process after droplet impact on porous surfaces is governed by the viscous dissipation and matric potential. The maximum-spread model predictions agreed well with experimental measurements reported in this paper and the literature over a large range of Weber numbers and different porous surfaces. [ABSTRACT FROM AUTHOR]

The paper addresses the problem of coupled heat and moisture transfer in porous materials with the time-periodic boundary conditions applied. The solution of Luikov equations [1] , which describe coupled heat and moisture transfer, is presented. Laplace transform is used, where some terms of the inverse Laplace transform ought to be solved by Gaussian quadrature, meaning that the solution is semi-analytical. The time-periodic boundary conditions are applied to simulate the humidity and temperature oscillations of natural environment. Therefore, the proposed solution is appropriate to evaluate the distribution of moisture and temperature within the porous material exposed to everyday natural cycles. The paper presents convergence tests, validation of semi-analytical solution and application to different building materials are presented in the paper. [ABSTRACT FROM AUTHOR]

The combination of the high conductivity of nanofluids with the huge accessible surface area of open-cell metal foam would indeed be a superb heat exchange technology. While individual ingredients of this technology have been separately investigated, the combination of the two has received only scant attention. Actually, there are only few studies that are focused on nanofluids flow and heat transfer in metal foam. This paper is intended to serve as an orientation for researchers who are interested in both nanofluids heat transfer and metal foam. The paper thus includes discussion of various aspects of nanofluids and their heat-transfer applications, as well as fundamentals of flow and heat transfer of ordinary fluids in metal foam. A section on recent heat transfer studies in metal foam is included, and another section on pore-scale modeling of transport in metal foam is provided. Nanofluids are presented in terms of their definition, brief history, preparation methods, theoretical models, properties, and engineering applications related to heat transfer. The paper then moves to describe metal foam and its morphology, as well as current understanding and theoretical treatment of flow and heat transfer in this class of highly-porous media. Key heat transfer and flow properties of the foam are outlined. The paper also presents the case for nanofluids forced convection heat transfer in open channels to serve as a background for the more complex case that involves heat transfer in porous media in general. The case of forced convection of nanofluids in metal foam in particular is presented next. Studies including complex effects, e.g. magnetism, are briefly described. Based on the above information, some key findings, conclusions and recommendations are made for interested researches. [ABSTRACT FROM AUTHOR]

• A novel laboratory-scale experimental setup to measure changes in moisture content of textiles during drum drying. • A simple mathematical heat transfer model to assess moisture changes in drum drying. • Quantification of the impact of interfacial thermal contact resistance on drying time. Drum dryers are widely employed in various industrial fields for their remarkable capability to efficiently dry thin porous materials such as textiles and paper. The heat transfer process in drum drying involves an interaction between the drum surface and the materials being dried. However, measuring interfacial thermal contact conductance during drum drying is very challenging, and little data has been reported in the literature. It is therefore unclear how changes in interfacial thermal contact conductance quantitatively affect drum drying in terms of drying time. We created an innovative laboratory-scale experimental setup designed to measure changes in moisture content of textiles at various contact pressures during drum drying. By combining our experiments with a simple yet effective heat transfer model, we were able to quantify the impact of interfacial thermal contact resistance on drying time. Specifically, in drying tests using thin cotton textiles, the experimental results revealed that when the contact pressure was increased from 120 Pa to 480 Pa, the thermal contact conductance increased by approximately 30% and the drying time decreased by approximately 20%. The outcomes of our study significantly advance the current understanding of drum drying processes and reveal vital insights into techniques for optimizing energy consumption. [ABSTRACT FROM AUTHOR]

The effective thermal conductivity (ETC) of composites is of great significance for simulating the macroscopic heat transfer process. In this paper, an extension of the morphology efficiency is proposed, which quantifies the influence of morphology on composite ETC, and is initially derived from two extreme models-series and parallel ETC bounds. The morphology efficiency obtained from different bound models are compared. It concluded that the morphology efficiency derived from Hashin and Shtrikman bound models is the best representative of the morphology of isotropic composite materials, which can conveniently reveal the optimal volume fraction of inclusion phase and thermal conductivity of the ideal thermal response. For composites with inverse Simple Cubic, Body Centered Cubic, Face-Centered Cubic and Kelvin lattice, the corresponding prediction model of ETC is proposed in a wide range of porosity and thermal conductivity. Among them, the ETC model of Kelvin cell and inverse Simple Cubic cell can well predict the high porosity foam and foams filled with phases with thermal conductivity ratio r in the range of 3 to 8, respectively. [Display omitted] • The best morphology factor is derived from Hashin–Shtrikman bounds. • The models for effective thermal conductivity (ETC) of regular lattices are proposed. • The ETC model of Kelvin cell can well predict the ETC of the high porosity foam. • The ETC model of SC cell can well predict the ETC of Al−Sn and Fe−Cu alloys. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) are frequently and widely used in latent thermal energy storage (LTES) system and thermal management (TM) system due to their large latent heats and capabilities of maintaining nearly constant temperature. However, the performances of PCMs in LTES and TM systems are seriously limited by their low thermal conductivities and poor heat transfer performances, which consequently stimulates intensive experimental and theoretical investigations on improving the thermal conductivities and heat transfer performances of PCMs by using different methods. The present paper reviews the recent progresses of the investigations and applications of the composite PCMs with the enhanced performance. The focuses are placed on the composite PCMs fabricated by using the metal foams and carbon materials, which have been proved to be the most promising approaches for thermal conductivity and heat transfer promotion on PCMs. The fabrication processes of the composite PCMs are first introduced in the present paper followed by the thermal characterization. The measurement of the effective thermal conductivities of the composite PCMs is discussed in detail by comparing different measuring methods, and the theoretical models to predict the effective thermal conductivities of the composite PCMs are also presented. The mathematical models describing the phase change heat transfer characteristics of the composite PCMs which are very important for system modeling and design are also addressed and discussed in the present review. Furthermore, the applications of the composite PCMs to LTES and TM systems are introduced and summarized by illustrating the typical examples. It can be understood that the composite PCMs can effectively improve the performances of LTES and TM systems, which therefore calls for the further investigation in this research field. Finally, the future research topics are suggested. [ABSTRACT FROM AUTHOR]

This paper reports a multiscale asymptotic analysis and computation for predicting heat transfer performance of periodic porous materials with radiation boundary condition. In these porous materials thermal radiation effect at micro-scale have an important impact on the macroscopic temperature field, which is our particular interest in this study. The multiscale asymptotic expansions for computing temperature field of the problem are constructed, and associated explicit convergence rates are obtained on some regularity hypothesis. Finally, the corresponding finite element algorithms based on the multiscale method are brought forward and some numerical results are given in details. The numerical tests indicate that the developed method is feasible and valid for predicting the heat transfer performance of periodic porous materials, and support the approximate convergence results proposed in this paper. [ABSTRACT FROM AUTHOR]

• Comprehensive experimental dataset for a plate-fin heat exchanger is presented. • Issues relating to the current heat exchanger manufacturing methods are stressed. • Novel heat exchanger corrugation modelling approach is developed. • Good aggrement of novel CFD is found in comparison to the experiments. The paper compares two serrated plate-fin Heat Exchanger (HE) corrugation modelling methods using Computational Fluid Dynamics (CFD). The first method follows closely recent literature studies and models a finite length single channel of a corrugation layer inside the HE core. The second method utilises the conjugate heat transfer methodology and models a section of the HE core with both cold and hot fluid streams separated by a solid conducting wall (HE corrugation). The results of latter model are then extrapolated for the full dimensions of a HE core layer to obtain flow and heat transfer characteristics. The conjugate heat transfer analysis methodology presented is novel and eliminates the need for analytical/empirical modelling currently widely used within industry. Furthermore, it provides more detailed information about the flow and heat transfer inside the HE core enabling potential for more efficient HE designs. Predictions at the corrugation level were carried out at 88 ⩽ Re corrug ⩽ 2957 with mesh independence studies completed for all the computational domains. The results obtained in the HE corrugation predictions were then implemented to the multi-scale HE unit model where the flow inside the HE core was modelled using two porous media simplifications whilst the heat transfer was simplified using the effectiveness source term. The HE unit predictions were validated against industrial experimental data with good agreement found between the numerical and experimental results. All the simulations were completed using the open-source CFD package OpenFOAM. [ABSTRACT FROM AUTHOR]

• Compound porous media model is proposed to simulate performance of U-tube HX. • The complicated U-tube bundle is divided into three porous media sections. • For each section, porous coefficients are obtained from empirical correlations. • Results of compound porous media approach are in good agreement with test results. • The proposed model shows the ability to correctly model a complex geometry HX. This paper describes a compound porous media model approach for numerical analysis to investigate the aero-thermal performance and characteristics of a flat top U-tube heat exchanger. The heat exchanger was considered as a combination of three sections; vertically straight tube section, bent tube section, and horizontally straight tube section. The porous media coefficients were obtained by using empirical correlations for the pressure drop and heat transfer for each section. The numerical results of the compound porous media model were compared to those of a conjugate heat transfer (CHT) CFD analysis, considering real tube geometry and experiments in order to validate the proposed compound porous media approach. The validation revealed that the proposed approach provides reasonable flow and heat transfer characteristics as well as the overall aero-thermal performance of the flat U-tube heat exchanger, with a considerable reduction of the required computational power. [ABSTRACT FROM AUTHOR]

• An MRT-LB model is developed for incompressible axisymmetric thermal flows in porous media at the REV scale. • The forcing and source terms are simple and contain no velocity or temperature gradient terms. • The thermal MRT-LB equation is consistent with the philosophy of the LB method. In this paper, a multiple-relaxation-time (MRT) lattice Boltzmann (LB) model is developed for simulating axisymmetric thermal flows in porous media at the representative elementary volume scale. In the present model, the flow field is solved by a D2Q9 MRT-LB equation based on the generalized non-Darcy model, while the temperature field is solved by a thermal MRT-LB equation using a non-orthogonal transformation matrix with the D2Q5 lattice. The present model has the following features. First, the forcing and source terms are simple and contain no velocity or temperature gradient terms. Second, the thermal MRT-LB equation is within the framework of the standard LB method and is consistent with the philosophy of the LB method. Owing to these features, the present model retains the inherent advantages of the standard LB method and is easy to implement. The present model is tested by simulating several typical axisymmetric thermal problems in porous media, and the numerical results indicate that the present model can serve as an accurate and efficient numerical tool for studying axisymmetric thermal flows in porous media. [ABSTRACT FROM AUTHOR]

Highlights • Self-rewetting fluids can enhance capillary evaporator performance. • The phase change is visualized. • The enhancement of capillary evaporator with self-rewetting fluids is explained. Abstract This paper presents an experimental study of the phase change phenomenon in a porous medium. The tested working fluids are pure water and butanol aqueous solutions with different concentrations. In contrast to ordinary fluids, the surface tension of self-rewetting fluids exhibits a positive gradient beyond a certain temperature value. The experimental results indicate that the use of self-rewetting fluids (water/butanol) as working fluid significantly improves the performance of the capillary evaporator by decreasing the casing temperature. To explain the heat transfer enhancement mechanism, the phase change phenomenon is visualized for the two working fluids. It is shown that as the applied power increases, the shape of the vapor pocket that developed within the porous wick also increases for pure water until it reaches a stable shape. With respect to self-rewetting fluids, the shape of the vapor pocket decreases with increasing applied power allowing more efficient mass and heat transfers. Wettability, capillary pressure and Marangoni forces are the factors related to surface tension and contact angle that seem to be responsible for this heat transfer improvement for self-rewetting fluids. [ABSTRACT FROM AUTHOR]

Highlights • Metal and carbon based materials are used to enhance the heat transfer rate in PCM. • Melting point of the PCMs becomes slightly lower for PCM/foam composites. • Higher porosity foams are suitable for convection heat transfer. • Latent heat and specific heats are reduced for PCM/foam composites. • Charging and discharging period of composite PCMs become lower. Abstract Phase change material (PCM) is promising media for thermal energy storage owing to its extensive value of latent heat (140–970 KJ/Kg). However, thermal conductivity of PCMs is too low which obstructs energy storage and retrieval rate. In recent days, thermally enhanced PCMs are considered promising materials for efficient heat transfer in many applications. This article designates the review on improved thermal properties and heat transfer of PCMs by using porous materials. Enhanced heat transfer of PCMs can be achieved using extended surfaces (triangular, conical, square, and rectangular fins), heat pipes, and addition of highly conductive nanoparticles (e.g. Cu, Al 2 O 3 , Au, SiC, SiO 2 and TiO 2). Major focus of this article is to study the enhanced heat transfer of PCMs through metallic (copper, nickel, and aluminum) and carbon based (carbon, graphite and expanded graphite) porous materials/foams. Effects of porosity and pore density on heat transfer, thermal conductivity, specific heat, latent heat and charging/discharging time are critically reviewed. Porous materials/foams are reported to be efficient for heat transfer/thermal conductivity enhancement by 3–500 times. Furthermore, correlations to find the effective thermal conductivity of PCM/foam are reported. Important applications of PCM/foam reported by different researchers are also discussed in this paper. Finally, conclusions and recommendations are presented to highlight the research gap in this area. [ABSTRACT FROM AUTHOR]

Abstract This paper reports a theoretical analysis of heat and mass transfer in the microchannels partially filled with porous materials and used in thermos-chemical microreactors. A first order catalytic chemical reaction is considered on the internal surfaces of a parallel-plates microchannel. The local thermal non-equilibrium approach along with two well-established porous-fluid interface models is employed to investigate the heat transfer within the porous section of the microreactor. The analysis further accounts for the finite thickness of the surrounding solid walls of the microchannel. The dispersion equations in both porous and clear sections of the microchannel are coupled with the fluid temperature through considering the thermal diffusion of mass. In addition, to enhance heat transfer in the partially-filled microchannel, the base fluid is replaced by a nanofluid. The results show that inclusion of the finite thickness of the walls in the thermal analysis can majorly affect the temperature fields and Nusselt number (Nu). In particular, the optimal thickness of the porous insert for achieving the maximum Nu is found to be strongly influenced by the wall thickness. It is also shown that the specific porous-fluid interface model, thicknesses of the porous section and that of the walls, and the volumetric concentration of the nanoparticles can all impart significant effects upon the concentration of chemical species and their distribution across the microchannel. More specifically, the concentration field within the porous region is found to be considerably dependent on the implemented porous-fluid interface model. Graphical abstract Schematic configurations of the model microreactor, and variation of Nusselt number with porous thickness. Image 1 Highlights • Thermal analysis of partially porous microreactors are performed. • Thermal diffusion and two models of BCs for interfaces are included in the investigation. • The effect of walls thicknesses on the thermal performance of the microreactor is studied. • Effects of Damköhler and Soret numbers on concentration contours are shown. • Effects of incorporating nanoparticles in the base fluid were investigated. [ABSTRACT FROM AUTHOR]

Highlights • Conditions for onset of dryout in a heat-releasing porous bed are considered. • Functional form of the dryout heat flux (DHF) is derived for three drag models. • A surrogate model for DHF derived in the form of three functions of single-argument. • Fast DHF calculation possible with accuracy acceptable for engineering applications. • Model application to multidimensional porous beds is discussed. Abstract This work is motivated by the problem of restraining temperature escalation inside a porous heat-releasing media submerged in a pool of liquid coolant. When coolant temperature reaches saturation, boiling begins in the bulk of the porous bed, with void generation rate determined by the heating power. Amount of void determines hydrostatic pressure difference that drives natural circulation of two-phase flow through the porous material. At a certain critical value of the heat release rate, the driving head cannot overcome drag of the two phase porous media flow, which results in complete evaporation of coolant in some zone. Temperature of material in the dry zone increases significantly due to deterioration of heat exchange with single phase vapor flow in comparison with boiling flow heat transfer. The paper considers the problem of determining the critical conditions for onset of dryout in a heat-releasing porous bed of an arbitrary shape. The well-known one-dimensional problem for a flat top-flooded bed is revisited, and the functional form of the dryout boundary (expressed as the dryout heat flux, DHF) is derived using non-dimensional parameters. Asymptotic behavior of the solution is analyzed, and, by the method of asymptotic interpolation, a surrogate model is proposed consisting of three single-argument, non-dimensional functions. It is shown that such a model provides acceptable accuracy even in the cases where complete similarity of solutions is not achieved. The results obtained provide important insights into the physics of the problem, reduce the number of free parameters, and enable fast evaluation of dryout conditions without the need of numerical solution of algebraic equations involved in the exact formulation. The ultimate goal of the surrogate model development, i.e. its application to multidimensional configurations, is discussed. [ABSTRACT FROM AUTHOR]

Highlights • Heat transfer rate dropped by increasing magnetic field and this reduction enhances by porosity. • By increasing the Hartmann number the effect of Rayleigh number decreases. • Double MRT LBM is a proper method to solve the flows such as MHD natural convection in porous media. • Increasing the Rayleigh number improve the effect of adding the MWCNT–Fe 3 O 4 nanoparticles. Abstract In this paper, a new double multi relaxation time (MRT) Lattice Boltzmann method (LBM) has been used to simulate magnetohydrodynamics (MHD) natural convection in a porous media. A new nanofluid named; multi-walled carbon nanotubes–iron oxide/water nanofluid (MWCNT–Fe 3 O 4 /water hybrid nanofluid) has been utilized to investigate the effect of nanoparticle on heat transfer. The thermo-physical properties of the nanofluid have been extracted from experimental results. D2Q9 and D2Q5 lattices are used to solve the flow and temperature fields respectively, and the effect of various parameters such as; Darcy number (Da) (10−2–10−1), Rayleigh number (103 ≤ Ra ≤ 105), porosity (0.4 ≤ ε ≤ 0.9), volume fraction of nanoparticles (0≤ Ø ≤ 0.003) and Hartmann number (0 ≤ Ha ≤ 50) have been investigated. Based on the present results, the new double MRT LBM is a proper method to solve the complex flows such as MHD natural convection in porous media. The results show that augmentation of Rayleigh number increases the heat transfer rate for all cases however by increasing the Hartmann number the effect of Rayleigh number decreases. Also, adding the nanoparticles enhances the average Nusselt number as increases 4.9% for Ra = 105, Da = 10−1, Ha = 50, and ε = 0.9 when the volume fraction of nanoparticles rises from 0 to 0.003. Results indicate that by enhancing Darcy number heat transfer rate increases and average Nusselt number improves by porosity. [ABSTRACT FROM AUTHOR]

Highlights: • Entropy generation and heat transfer of the nanofluid are explored. • The nanofluid is under the influences of the electric field and magnetic field. • The nanofluid flow is confined to a porous microtube. • The variations of velocity, temperature, Nusselt number of the nanofluid are discussed. Abstract The purpose of this paper is to focus on the heat transfer characteristics of thermally developed electrokinetic flow of the nanofluid (water-Al 2 O 3) through a porous microtube in the presence of the imposed magnetic field. The wall of the microtube is subjected to the constant heat fluxes. Moreover, the local thermal equilibrium (LTE) model is considered. Combining with the electrokinetic effects of the wall, and utilizing the Brinkman model for the nanofluid flow in the porous medium, the conservative partial differential equations have been transformed into the ordinary equations. The analytical solution of velocity and numerical solution of temperature are derived based on relevant dimensionless parameters. Furthermore, the Nusselt number, local and total entropy generation analyses are further examined qualitatively. [ABSTRACT FROM AUTHOR]

Highlights • Two observed heat transfer regimes: reduced heat transfer regime at lower Rayleigh numbers, asymptotic regime at higher Rayleigh numbers. • Convective heat transfer for all sphere conductivities, sizes, and packings converge to the curve for Rayleigh-Bénard convection. • In the asymptotic regime, the flow penetrates into the porous layer leading to much higher velocity in the core region. • The comparison between thermal length scales and porous length scales determines the flow structure and heat transfer in porous media. Abstract This paper reports on an experimental study of natural convection in an enclosure that is heated at the bottom and cooled at the top, filled with a packed bed of relatively large solid spheres. Nusselt numbers were measured for various sphere conductivities, spheres sizes and sphere packings for Rayleigh numbers varying between 107 and 109. The Nusselt number measurements showed that at lower Rayleigh numbers, the heat transfer is lower than that for pure Rayleigh-Bénard convection, with the difference depending on packing type, size, and conductivity of the spheres. However, at high Rayleigh numbers, there exists an asymptotic regime where the convective contribution of the total heat transfer for all sphere conductivities, sizes, and packing types collapse on a single curve which is very close to the curve for pure Rayleigh-Bénard convection. Refractive index-matching of the fluid and the solid spheres enabled the use of particle image velocimetry and liquid crystal thermography to obtain highly resolved velocity and temperature fields. The comparison of the velocity and temperature fields for the two heat transfer regimes showed that the velocity magnitudes inside the pores in the core region are much higher in the asymptotic regime than those in the low Rayleigh number regime, which lead to a deeper penetration of cold and hot fluid elements and higher heat transfer. [ABSTRACT FROM AUTHOR]

Highlights • Review summarizes constructal optimizations about engineering problem in China. • Six classes of objects are included performed over the past decade. • Multi-disciplinary, multi-objective and multi-scale constructal optimizations. • A model of generalized transfer process based on various transfer processes. Abstract Constructal theory has been widely used in performance optimizations of various problems. Among these problems, engineering problem is a hot topic for constructal theory. The developments of constructal theory about engineering problem in China over the past decade are reviewed in this paper. Multi-disciplinary, multi-objective and multi-scale constructal optimizations of various transfer processes in engineering, such as heat conduction and thermal insulation processes, fluid flow processes, convective heat transfer processes of fins, heat sources, cavities, cooling channels, vascular networks and heat exchangers, mass transfer processes of porous mediums, heat and mass transfer processes of solid-gas reactors and solid oxide fuel cells, iron and steel production processes and generalized transfer processes, have been conducted since 2006. Performance improvements are realized, new design requirements are satisfied, and more practical and generalized results are obtained after new research objects, model improvements, optimization objectives, boundary conditions, constraint conditions and transfer extensions are considered. It shows that the developments of constructal theory are still being made in China, which will provide more design guidelines not only for engineering problem, but also for natural and social problems. [ABSTRACT FROM AUTHOR]

Highlights • Moisture content in non-hygroscopic insulation materials was measured by a heating needle. • Test domain was released from the required infinite dimension to a finite thickness. • CFD modeling was adopted to correct the boundary heat loss effect. • The remedial strategy provided moisture content close to the gravimetric values. Abstract Porous insulation materials may acquire moisture, and the moisture content must be accurately measured for appropriate maintenance of the materials. Current thermal methods for measuring moisture are applicable only to an infinite test domain. This paper used computational fluid dynamics (CFD) to investigate the effects of a finite test domain and the associated boundary heat loss on moisture measurement. Insulation material of various thicknesses, bounded by two solid plates, was modeled. The convective heat loss to the air from both solid plates was considered. The over-measured moisture content due to a finite geometric domain was regressed into formulas, by means of which the excessive amount could subsequently be deduced. The corrected moisture content was then compared with that obtained by gravimetric weighing using a digital precision balance. The results show that significant over-measurement of moisture content can occur for the tested insulation material with a thickness less than 4.5 cm. The remedial strategy is quite effective and can provide moisture content results that are close to the gravimetric values. [ABSTRACT FROM AUTHOR]

Abstract The advancements in the materials science and the ability of manufacturing new materials, make it possible for engineers to use the porous medium as a solid body that provide maximum surface contact with the fluid. In this paper, to increase the contact surface area and decrease the flow resistance, the solid tapered fins replace with porous one and its effect on convective heat transfer is investigated for different Reynolds number. To do this, first the heat transfer of the rigid tapered fins is studied and validated, then, the solid body is changed to the porous one and the influence of the Reynolds number was investigated on the heat transfer and pressure drop. The results show that in laminar flow the Nusselt number of the flow with porous medium is 33% higher and the pressure drop is 9.35% lower than the rigid one with the same conditions. Therefore the application of the porous medium at low velocities is much recommended but with increasing the velocity, the porous media is not preferable. Also, for the problem of flow around a bundle of porous tapered fins, an equation for Nusselt number is presented based on the Reynolds number. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a review of studies on natural convection heat transfer in the triangular enclosure namely, in attic-shaped space. Much research activity has been devoted to this topic over the last three decades with a view to providing thermal comfort to the occupants in attic-shaped buildings and to minimising the energy costs associated with heating and air-conditioning. Two basic thermal boundary conditions of attic are considered to represent hot and cold climates or day and night time. This paper also reports on a significant number of studies which have been performed recently on other topics related to the attic space, for example, attics subject to localized heating and attics filled with porous media. [Copyright &y& Elsevier]

Highlights • The heat transfer flow of a Walters’ liquid B in a porous medium with Navier slip is investigated. • The physical problem is modelled into nonlinear PDE’s to ODE’s via similarity transformation. • The analytical solutions derived for velocity and temperature fields by Kummer’s function. • Temperature profiles are analyzed for two type of boundary heating processes namely PST and PHF. • The temperature distribution inside the stretching sheet is found to be controlled by Pr, N R and N I. Abstract This paper investigates the steady-state momentum and radiation heat transfer flow of a viscoelastic fluid in a porous media in the presence of a linear Navier slip boundary condition. The velocity of the fluid over the linear stretching sheet is varied linearly with the axial distance while a Walters’ liquid-B model is assumed for the viscosity. A similarity transformation reduces the Navier–Stokes equations to a set of partial differential equations that are converted into ordinary differential equations and solved analytically for the velocity. Moreover, heat is balanced between a temperature dependent heat source and radiation and leads to a differential equation with variable coefficients. The temperature equation is transformed to a confluent hypergeometric differential equation using the Rosseland approximation for the radiation and solved analytically. Results are discussed for two boundary conditions of the sheet, the prescribed surface temperature and the wall heat flux. Parameters like the Reynolds number, the viscoelastic parameter and the boundary slip parameter are found to determine the flow field. In addition, the Prandtl number, the radiation number, the wall temperature and the heat source/sink parameters are found to control the temperature distribution inside the stretching sheet. [ABSTRACT FROM AUTHOR]

The technology of fire prevention and extinguishing using liquid nitrogen or cryogenic nitrogen has been widely applied in underground coal fire. In this paper, a multi-scale model has been proposed to investigate the complex heat transfer characteristics in coal porous media (CPM) with cryogenic nitrogen injection. In the model, the fluid energy equation at representative elementary volume (REV) scale is coupled with the heat conduction equation of a solid particle at pore scale considering the temperature variation in the coal particle, and the equivalent diameter is employed to simplify the heat conduction process in the solid particle. The experiment has been carried out and the result is consistent with the simulation obtained by the multi-scale model. The influences of equivalent diameter, mass flow rate, inlet fluid temperature and initial temperature on the local thermal non-equilibrium (LTNE) effects have been investigated numerically by using the multi-scale model. The results show that the time to reach local thermal equilibrium (LTE) between fluid and solid center is longer due to the small thermal conductivity of coal matrix, and it is affected dramatically by equivalent diameter and mass flow rate. The results also indicate that the inlet fluid temperature and initial temperature of CPM have important influence on the temperature difference between solid center and fluid. [ABSTRACT FROM AUTHOR]

An accurate estimation of building material thermal conductivity is crucial for the modeling of heat transfer processes and the calculation of building energy consumption. The effect of moisture content on the thermal conductivity of the material is usually neglected in most currently used calculation methods. These methods cannot represent the interior multi-phase heat transfer process. In this paper, the coexisting solid-liquid-gas thermal conductivity physical model was proposed. Taking into account the pore structure characteristics of building materials, a coexisting tri-phase thermal conductivity calculation model based on capillary structure was established using fractal theory. The quantitative influence relationship of the parameters, such as porosity, pore diameter distribution, moisture content and fractal structure, on the thermal conductivity of moist porous materials was analyzed. The results provide a theoretical basis for the thermal conductivity correction of moist building materials. [ABSTRACT FROM AUTHOR]

Abstract: The present review is intended to encompass the heat transfer literature published in 2005. While of a wide-range in scope, some selection is inevitable. We restrict ourselves to papers published in English through a peer-review process, with selected translations from journals published in other languages. Papers from conference proceedings generally are not included, though the Proceeding itself may be cited in the introduction. A significant fraction of the papers reviewed herein relates to the science of heat transfer, including experimental, analytical and numerical studies. Other papers cover applications where heat transfer plays a major role, not only in man-made devices but in natural systems as well. The papers are grouped into major subject areas and then into subfields within these areas. In addition to reviewing the literature, we mention major conferences held in 2005, major awards related to heat transfer presented in 2005, and books on heat transfer published during the year. [ABSTRACT FROM AUTHOR]

Abstract: Pool boiling heat transfer with porous media as the enhanced structure is attractive due to its simple geometry and easy operation. However, the available studies focus on low porous porosities. Metallic foams provide large porous porosities that have been less studied in the literature. In this paper a set of copper foam pieces were welded on the plain copper surface to form the copper foam covers for the pool boiling heat transfer enhancement. Water was used as the working fluid. Enhancement of pool boiling heat transfer compared with plain surface depends on the increased bubble nucleation sites, extended heat transfer area, and resistance for vapor release to the pool liquid. Effects of pores per inch (ppi) of foam covers, foam cover thickness, and pool liquid temperatures are examined. It is found that temperatures at the Onset of Nucleate Boiling (ONB) are significantly decreased on copper foam covers compared with on plain surfaces. Heat transfer coefficients of foam covers are two to three times of the plain surface. A large ppi value provides large bubble nucleation sites and heat transfer area to enhance heat transfer, but generates large vapor release resistance to deteriorate heat transfer. Therefore an optimal ppi value exists, which is 60 ppi in this paper. Generally small ppi value needs large foam cover thickness, and large ppi value needs small foam cover thickness, to maximally enhance heat transfer. Effect of pool liquid temperature on the heat transfer enhancement depends on the ppi value. For small ppi value such as 30 ppi, lower pool liquid temperature can dissipate higher heat flux at the same wall superheat. However, the heat transfer performance is insensitive to the pool liquid temperatures when large ppi values such as 90 ppi are used. [Copyright &y& Elsevier]

Abstract: In this paper, a mathematical model is proposed for predicting air temperature and humidity in a two-room region. The model contains a coupled relationship between temperature and humidity within the constructions and can be solved by using the numerical method. However, the two-room region can be reduced to a single region when the region with no ventilation is considered, and then the room temperature and relative humidity can be obtained analytically. The solution obtained in this paper is verified by comparing with the result of the analytical method. It shows that the two results are in agreement. In addition, the proposed model can also be applied to simultaneously obtain the transient temperature and humidity of a two-room region for different porous construction materials. [Copyright &y& Elsevier]

Abstract: The process of heat transfer within porous media is usually considered as a transport through large numbers of straight channels with uniform pore sizes. For the prediction of effective thermal conductivity of gas diffusion layer (GDL), morphological properties such as the tortuosity of channels and pore-size distribution of this porous layer should be considered. Thus in this article, novel parallel and series-parallel prediction models of effective thermal conductivity for the GDL in proton exchange membrane fuel cell (PEMFC) have been derived by fractal theoretical characterization of the real microstructure of GDL. The prediction of fractal parallel model for carbon paper, a basal material of the GDL, is in good agreement with the reference value supplied by Toray Inc. The prediction results from the proposed models are also reasonable because they are distributed between the upper and lower bounds. Parametric effect has been investigated by using the presented models in dimensionless formalism. It can be concluded that dimensionless effective thermal conductivity () has a positive correlation with effective porosity (ɛ) or the pore-area fractal dimension (D p) when k s/k g <1; whereas it has a negative correlation with ɛ or D p when k s/k g >1 and with tortuous fractal dimension (D t) whether k s/k g <1 or not. Furthermore, these fractal models have been modified by considering the effect of polytetrafluoroethylene (PTFE) incorporated into the pore spaces of carbon paper, and the corresponding model prediction shows that there is an increase in the effective thermal conductivity due to the filling of PTFE that has high thermal conductivity. [Copyright &y& Elsevier]

Abstract: This paper deals with the theoretical investigation of the double-diffusive convection in a micropolar ferromagnetic fluid layer heated and soluted from below saturating a porous medium subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained. A linear stability analysis theory and normal mode analysis method have been carried out to study the onset of convection. The influence of various parameters like medium permeability, solute gradient, non-buoyancy magnetization and micropolar parameters (i.e. coupling parameter, spin diffusion parameter and micropolar heat conduction parameter) has been analyzed on the onset of stationary convection. The critical magnetic thermal Rayleigh number for the onset of instability is also determined numerically for sufficiently large values of buoyancy magnetization parameter and results are depicted graphically. The principle of exchange of stabilities is found to hold true for the micropolar ferromagnetic fluid saturating a porous medium heated from below in the absence of micropolar viscous effect, microinertia and solute gradient. The oscillatory modes are introduced due to the presence of the micropolar viscous effect, microinertia and solute gradient, which were non-existent in their absence. In this paper, an attempt is also made to obtain the sufficient conditions for the non-existence of overstability. [Copyright &y& Elsevier]

Abstract: While the transfer equations for moisture and heat in building components are currently undergoing standardisation, atmospheric boundary conditions, conservative modelling and numerical efficiency are not addressed. In a first part, this paper adds a comprehensive description of those boundary conditions, emphasising wind-driven rain and vapour exchange, the main moisture supply and removal mechanism, respectively. In the second part the numerical implementation is tackled, with specific attention to the monotony of the spatial discretisation, and to the mass and energy conservation of the temporal discretisation. Both issues are illustrated with exemplary hygrothermal simulations. Numerical efficiency is treated in two follow-up papers. [Copyright &y& Elsevier]

Abstract: This paper deals with natural convection driven by combined thermal and solutal buoyancy forces in a binary fluid. The configuration under study is a confined enclosure partially filled with a vertical porous layer. The mathematical description of the problem is based on a one-domain formulation of the conservation equations. The set of numerical results presented here quantitatively shows the influence of the porous layer on the flow structure and on heat and species transfer in the enclosure. The paper is focused on the analysis of the influence of the characteristic parameters governing double diffusive convection, namely the ratios of solutal and thermal parameters: the diffusivities and the buoyancy forces. Heat and mass transfer is analyzed as a function of the permeability of the porous layer. It is shown that the coupling of the flow penetration in the porous layer with the combined buoyancy forces induces a specific behavior of the flow structure and average heat transfer in the enclosure. [Copyright &y& Elsevier]

An action of CNTs flow access an unstable motion of a Newtonian fluid past a stagnation point on a stretched sheet using a penetrable medium is investigated in this paper. Once the fluid commences circulating with the flow of time, it flows. Flow is influenced by heat exchange with the surroundings. The implicitly limited component method is employed to track an unstable system of non-dimensional PDE with an associated boundary layer. Approaches, along with the relevant barrier circumstances, are acquired analytically. An influence of mass transpiration, volume fraction, and thermal radiation is investigated on Newtonian fluid flow using the penetrable medium. Heat transmission in a liquid with electrical conductivity, including heat source /sink across a continually stretched /shrinking surface with a Biot number. The importance of the present exertion is the stream of carbon nanotubes owing to Darcy porous media using linear heat radiation and an analytical approach. The nanoparticles provide important properties in enhancing the heat exchange procedure as well as thoroughly achieved applications in industry. It is discovered that the basic resemblance models accept two-phase for both extending /contracting sheets. In presence of calculation upon momentum with temperature jump conditions is accessible plots aimed at varying predictions of certain physical properties. Analyzing the properties of Darcy porous media of heat transport in the presence of radiation from a flat surface, the problem is solved analytically using incomplete gamma functions. Depending on the kind of boundary heating, the analytical equation for temperature is obtained in terms of power series. • Unsteady flow over permeable plates in porous media with thermal radiation is studied. • The analytical solution is obtained by using incomplete gamma functions. • Velocity and temperature are presented in terms of power series depending on BCs. • Effects of physical parameters on the flow and heat transfer are characterized. • Velocity boundary layer decreases and thermal boundary layer increases in porous media. [ABSTRACT FROM AUTHOR]

In this paper, a three-dimensional simulation of fully coupled multiphase fluid flow and heat transfer through deforming porous media is presented in the context of EFG mesh-less method. Spatial discretization of the system of governing equations is performed using EFG and a fully implicit finite difference scheme is employed for temporal discretization. Penalty method is used for imposition of essential boundary conditions. The developed numerical tool is employed to simulate two problems of nuclear waste disposal and CO 2 sequestration in deep underground strata. The obtained results demonstrate the capability and robustness of the developed EFG code. [ABSTRACT FROM AUTHOR]

In this paper, the lattice Boltzmann method is applied to investigate the effects of uniform vertical magnetic field on thermo-hydrodynamics of nanofluid in a partially porous channel. Cu-water nanofluid with constant pressure gradient is forced to flow into the channel while the top wall is heated by constant heat flux and bottom wavy wall of the channel is insulated against heat. The porous media is modeled using the Brinkman–Forchheimer model. Good agreements with the previous results verify that the selected numerical method is a capable method for simulating magnetic fluids in a porous media. The effects of active parameters, i.e. solid volume fraction of nanoparticles, pressure gradient, magnetic field and permeability of the porous layer, on thermo-hydrodynamics of flow are examined. The results reveal that the Nusselt number is an increasing function of nanoparticle volume fraction, Hartmann number, pressure gradient and Darcy number, although the effect of Darcy numbers and pressure gradient on the temperature profile are more noticeable than others. [ABSTRACT FROM AUTHOR]

A high pressure, efficient and power dense air compressor/expander is a critical element in an isothermal compressed air energy storage (ICAES) system. Heat transfer is often the limiting factor in realizing efficient and power dense compression and expansion processes. Liquid piston compressor/expanders with porous media inserts have been proposed, in which the porous media serves as heat exchangers. While this concept has been studied through modeling and simulation, it has only been validated experimentally at low pressures (10 bar). This paper studies experimentally the effect of porous media in a high pressure (7–210 bar) liquid piston air compressor/expander, which is the proposed pressure for the ICAES system. Cases with the porous media uniformly distributed and non-uniformly distributed in the chamber are studied with various compression and expansion rates. Results show that at 93% efficiency, the uniformly distributed 2.5 mm interrupted plate porous medium increases power density by 10 times in compression and 20 times in expansion; or at the same power, efficiency is increased by 13% in compression and 23% in expansion. Moreover, the porous medium, if deployed at the top of the chamber, is shown to be more effective than if deployed at the bottom. The results indicate that the added surface area provides the dominant benefits but the porous media also increase the heat transfer coefficient at the same efficiency regime. These results are consistent with and extend the findings from previous low pressure experiments. [ABSTRACT FROM AUTHOR]

Fractured vuggy porous media continue to challenge the flow simulation research involving mass and/or heat transfer processes. Here, we report a coupled multiscale and multi-continuum approach developed to improve the modeling of multiphase flow through fractured vuggy porous media involving multi-continuum mass transfers. Multiple levels of fractures can be not only modeled as different superimposed continua but also embodied as discrete fracture networks based on their geometrical characteristics. Different configurations of vuggy existence can also be handled by a continuum and/or their discrete representations. We develop a systematic coupling using Multiscale Finite Element Method (MsFEM) as a framework for coarsening and refinement. MsFEM is used to capture subgrid scale heterogeneities and interactions through multiscale basis functions calculated based on the multi-continuum background. Unstructured mesh is applied to model discrete fractures in arbitrary directions and discrete vugs with complex geometries. This paper presents a significant advancement in terms of elevating the limitations of the multi-continuum models in handling complex fracture and/or vug geometry and extending the model reduction capability of MsFEM. Several numerical examples are carried out to demonstrate the capability of the proposed coupling method. [ABSTRACT FROM AUTHOR]

In this paper, thermal and hydrodynamic characteristics in microchannel heat sinks are studied to determine the parameters required in modeling heat sinks as fluid saturated porous medium. A three-dimensional conjugate heat transfer model is developed for characterizing fluid flow and heat transfer in microchannel heat sinks. This numerical model is first validated with the results reported in literature. For effective modeling of heat sinks, two different porous medium models are studied, namely Darcy and Forchheimer flow models. Darcy flow model is used for characterizing hydrodynamically and thermally developed flow and Forchheimer model is considered for the developing flow. The regime of applicability of these models is specified in terms of non-dimensional parameter, Forchheimer number. It is found that for Forchheimer number greater than 0.008, the Forchhiemer flow model is more appropriate as compared to Darcy flow model. A generalized expression for permeability with aspect ratio of the channel is obtained. The average Nusselt number defined based on modified heat flux and modified length scale is found to remain constant for different aspect ratios and porosities of microchannel heat sink. The velocity and temperature profiles obtained from the present porous medium model, porous model reported in literature and three-dimensional microchannel heat sink are compared and a good agreement is achieved between present and three-dimensional model. The present model can be used as a reduced order model for analyzing microchannel heat sinks with entrance effects. [ABSTRACT FROM AUTHOR]

In this paper, dispersion effects on forced convection heat transfer in a gaseous slip flow through a microtube filled with anisotropic porous medium are investigated semi-numerically. Microtube is subjected to constant heat flux and a local thermal non-equilibrium condition is assumed. Rarefaction effects are taken into account by applying first-order velocity slip and temperature jump boundary conditions. Dispersion is proven to have a significant impact on heat transfer in rarefied gases. Temperature distributions for both solid and fluid phases are obtained. Nusselt number variation with respect to porous shape factor and Biot number is illustrated, indicating enhancement up to 10% in predicted heat transfer due to dispersion. The influence of Reynolds number on thermal dispersion is proven to be insignificant. Dispersion plays a significant role as gas becomes more rarefied. It is seen that an increase in shape factor of a porous media can improve Nu for a non-rarefied gas, but as rarefaction effects grow, this can affect heat transfer negatively. Also, effects of dispersion on heat transfer diminishes for higher values of Biot Number due to the overcoming of interstitial heat transfer to thermal dispersion effect. [ABSTRACT FROM AUTHOR]

The flow pattern and heat and mass transfer in the porous media and fluid mixing area are widely found in the production and engineering, such as heat pipe, building envelope and insulation materials. Especially the slip effect at the at the interface between the fluid and the porous media has a great impact on the flow and heat and mass transfer. Therefore, the processing of the interface in the mixed area is the focus of many studies. In this paper, the mixed area of fluid and porous media is studied by means of theoretical analysis and numerical simulation. The numerical simulation of the mixed region is carried out by using the single domain method. The purpose of controlling the entire mixing area with a set of control equations is achieved by controlling the source terms which are defined by the user-defined function (UDF) in Fluent. And the accuracy and feasibility of the procedure are verified by comparison with numerical simulation of double domain method. Then, by discussing the influence of different physical parameters on the slip characteristics at the interface between fluid and porous media, the mechanism of velocity slip effect is summarized, which lays the foundation for the study of heat transfer and mass transfer. [ABSTRACT FROM AUTHOR]

A lattice Boltzmann model is applied to simulate natural convection of porous media in closed square cavity. The numerical simulation is conducted to investigate the influences of porosity on fluid flows and the effect of thermal conductivity ratio of solid matrix to fluid on heat transfer. Micro X-CT has been used to obtain 2D optical image of various slice with different location. A construction porous model has been established accurately by 2D optical micro X-CT image of porous media. A fluid –solid conjugate heat transfer model has been applied to the established construction porous model by using Lattice Boltzmann method.This paper confirms the reliability and the computational efficiency of the lattice Boltzmann method in simulating natural convection in porous media at mesoscopic pore-scale.The temperature field is simulated by a simplified thermal energy distribution function which neglects the compression work done by the pressure and the viscous heat dissipation. A comprehensive parametric study of natural convective flows is carried out for various values of Rayleigh number. [ABSTRACT FROM AUTHOR]