Interstitial Heat Transfer Research Articles

Effects of Channel Flow Blockage on Metal Foam Heat Transfer

Abstract High porosity aluminum foams have the potential to dissipate large heat flux in a channel flow configuration due to their large surface area-to-volume ratio and the ability to enhance mixing due to flow tortuosity. It is well documented that the interstitial heat transfer coefficient has a power law dependence on the flow velocity at the pore-scale. For asymmetrical heating (single wall), a flow blockage concept is proposed with an aim to locally enhance flow speed near the heated wall. To this end, experimental and numerical investigation is carried out on a high porosity (95%) aluminum foam (10 pores per inch) with flow blockages, both upstream and downstream of the metal foam placed in a square channel. The opening was provided closer to the heated wall, where flow blockage was varied from 0% to 87%. With air as working fluid, experiments were conducted for channel Reynolds number varying from 3000 to 13,000. It was found that all flow blockages resulted in enhanced heat transfer over no-blockage case, however, at a high pressure drop penalty. An upstream flow blockage of 70% was found to have the highest thermal-hydraulic performance among other flow blockages (including 0% blockage).

Heat transfer model for moving packed-bed particle-to-sCO2 heat exchangers integrated with metal foams

Particle-to-supercritical carbon dioxide (sCO2) heat exchangers (HXs) play a vital role in coupling heat transfer fluid (HTF) from high-temperature thermal receivers to power cycle working fluids (WF). Heat transfer enhancement is essential for adopting particle-based moving packed-bed heat exchangers (MPBHXs) in next-generation thermal energy storage (TES) systems, as MPBHXs usually exhibit low particle bed-to-wall heat transfer coefficients. High-porosity metal foams have shown their effectiveness in heat transfer enhancement. This work presents a continuum heat transfer model to demonstrate the heat transfer enhancement in MPBHXs when the particle bed channel is filled with high porosity metal foams compared to open channel MPBHXs. The presence of metal foams increases the effective thermal conductivity in the particle channel and enhances the interstitial heat transfer coefficient between the moving particle bed and the stationary metal foams. The present model considers coupled two-dimensional (2D) heat transfer in the particle channel with metal foams and 1D heat transfer in the sCO2 channel and the dividing wall. The temperature profiles for the particle bed, metal foam, dividing wall, and sCO2 stream, as well as the local heat flux profiles between those, are studied in detail for various foam porosities, from which the particle bed-to-wall heat transfer coefficient, overall heat transfer coefficient, and total heat transfer rate for the MPBHX are determined. The effects of major MPBHX design and operating parameters on the particle bed-to-wall heat transfer coefficient and overall heat exchange capacity are thoroughly examined; thus, the MPBHX performance improvement with metal foams is quantified for each case. The present heat transfer model can provide valuable insights into the metal-foam MPBHX design and optimization, scale-up, and operating parameters selection.

Effects of porous medium filling on thermally developing forced convection in a parallel plate channel

This study obtains the semi-analytical solutions and explores the thermal characteristics of a thermally developing flow in a parallel plate channel, partially filled with a porous medium at the core, while considering local thermal non-equilibrium conditions, and viscous dissipation for the first time. The developing temperature field, for a porous medium filling of volume fraction fixed at 0.9, indicates an increasing difference in temperature between the solid and fluid phases with the axial distance. Besides, heat flux bifurcation starts in the entrance region as more heat diffuses to the solid at the interface, more markedly with a decreasing Darcy number, Da. When the thermal transport is dominated by interstitial heat transfer between solid and fluid in the porous medium, the thermal entrant length is the shortest. An increasing amount of porous medium filling with such quality and an increasing Da tend to shorten the thermal entry length. Nonetheless, as a lower Da porous media convects more heat away from the interface, it expedites the thermal development in cases where interstitial heat transfer in porous medium is poor. With an increasing porous medium fraction, the impact of viscous dissipation on heat transfer magnifies at the entrance region, thereby reducing the effectiveness of porous medium insert.

Thermodynamic optimization of a linear thermomagnetic motor

Thermomagnetic motors can be applied to recover low-grade thermal energy waste and convert it into mechanical energy, therefore, used as an energy harvester. The present work proposes a mathematical model to simulate the heat transfer and the thermodynamic cycle of a linear thermomagnetic motor coupled to a spring mechanism. The simulation results are the input information in a subroutine to optimize the motor design based on two objective functions: to minimize the total entropy generated and to minimize the back work ratio, defined as the ratio between the pumping power and the total produced power. The mathematical model solves coupled the energy equations for the fluid and solid phases, and the entropy generation model includes four contributions: interstitial heat transfer (finite temperature difference), axial conduction in the fluid and solid phases, and viscous dissipation. Gadolinium is used as soft magnetic material due to the availability of properties data. Four design and operating conditions constraints are taken into account: heat exchanger length, spring constant, mass flow rate, and warm stream temperature (heat source), and their optimized values are, respectively, 52 mm, 1560 N/m, 80 kg/h at any warm stream temperature ranging from 310–330 K. At these combinations, the optimum thermomagnetic motor is able to produce a net power of 5.00 ± 0.15 W with a minimum back-work ratio of about 12%. The proposed methodology can be used to optimize the design of novel thermomagnetic motors or to optimize geometric parameters and operating conditions of state-of-the-art concepts.

Comparison on the heat transfer performance and entropy analysis on miniature loop thermosyphon with screen mesh wick and metal foam

Comparison on the heat transfer performance (HTP) of copper screen mesh wick and metal foam inserted evaporator section of miniature loop thermosyphon is experimentally investigated. Porosity of both screen mesh wick and metal foams are fixed to be 63%. Experiments are conducted using DI water under vertical orientation for different heat loads (40 W–280 W) and filling ratios (FR = 20%, 30% and 40%). Results showed a decrease of 12.8% and 5.2% in thermal resistance and wall temperature respectively for the metal foam inserted evaporator. In addition 10.6% enhancement is noted for heat transfer coefficient at the evaporator region for 30% FR. Reduction of 4.6% in heat transfer irreversibility is also noted for metal foam inserted thermosyphon compared to screen mesh wick condition. Increase in interstitial heat transfer between the fibers of metal foam and larger pore size of metal foams resulted in higher permeability compared to screen mesh wick are responsible for the enhancement in the overall HTP of metal foam inserted thermosyphon. Based on the observed results, the use of metal foams inserted thermosyphon will be a better substitute for thermal management applications of electronic devices.

A comprehensive study on the heat transfer characteristics of windward bend lattice frame structure

The windward bend lattice frame structure (WB structure) is characterized by a high heat transfer coefficient and low friction factor. The WB structure can be applied for thermal protection system, protecting outer walls of afterburner and nozzles from being damaged by the heating load of hot gas, for air cooling system of the power battery module, dissipating the heat generated during its charging and discharging. In this paper, the heat transfer characteristics of the windward bend lattice frame structure have been comprehensively studied. A systematic 3D numerical simulation has been conducted to investigate the effects of the structural parameters of the WB structure, including the pitches in both flow direction and transverse direction, the diameter and the inclination angle of windward bend ligament, on its flow resistance and heat transfer enhancement, which has been evaluated by comparing its Nusselt number under an equal pumping power. Furthermore, the contribution of an important parameter, i.e., the ratio of the interstitial heat transfer rate to the end-wall heat transfer rate (RQ), to the overall heat transfer rate has been fully discussed. As a result, the case of 6 units in the longitudinal direction and 2.5 units in the transverse direction, i.e. (nx = 6, nz = 2.5) exhibits the best performance in the light of the value of the Nusselt number. Moreover, the structure with a ratio of RQ ranges in 4.5–5.0 achieves a better heat transfer performance. Finally, two color contour graphs showing an optimal range of Nusselt number coordinated by unit numbers (nx, nz) for pumping powers of 2500 and 3000 have been presented. The graphs correctly reflect the variation of Nusselt numbers of structures with different nx and nz, and the conclusions remain consistent with the discussion in sections 4.2 and 4.3, instructing the reasonable selection of structural parameters of a thermal protection system embedded with WB structure.

Numerical Model for Heat Transfer in Layered Soil with Local Thermal Nonequilibrium

A numerical model, called HT2, is presented for one-dimensional heat transfer in saturated incompressible layered soil with steady fluid flow, effective porosity, and possible local thermal nonequilibrium (LTNE) between solid and fluid phases. The model uses a series-parallel approach and accounts for advection, conduction, linear and nonlinear thermal dispersion, and interstitial heat transfer. The key to HT2 is the definition of separate columns for the solid matrix (SM) and mobile pore fluid (MPF). The SM column includes the solid phase and immobile pore fluid and consists of fixed elements. The MPF column consists of moving elements and uses Lagrangian element-tracking to follow the fluid motion, which reduces numerical dispersion and simplifies heat transfer within the column to that of dispersive flux between contiguous elements. The model uses an interstitial heat transfer coefficient to calculate kinetic heat transfer between SM and MPF elements. The development of HT2 is first presented, followed by verification checks and a limited parametric study. Numerical simulations indicate that larger particle size and higher fluid discharge velocity yields greater local temperature disequilibrium between solid and fluid phases during heat transfer through saturated soil.

Correlations and Numerical Modeling of Stacked Woven Wire-Mesh Porous Media for Heat Exchange Applications

Metal foams have gained attention due to their heat transfer augmenting capabilities. In the literature, correlations describing relations among their morphological characteristics have successfully been established and well discussed. However, collective expressions that categorize stacked wire mesh based on their morphology and thermo-hydraulic expressions required for numerical modeling are less explored in the literature. In the present study, cross relations among the morphological characteristics of stacked wire-mesh were arrived at based on mesh-size, wire diameter and stacking type, which are essential for describing the medium and determining key input parameters required for numerical modeling. Furthermore, correlation for specific surface area, a vital parameter that plays a major role in interstitial heat transfer, is provided. With the arrived correlations, properties of stacked wire-mesh samples of orderly varied mesh-size and porosity are obtained for various stacking scenarios, and corresponding thermo-hydraulic parameters appearing in the governing equations are evaluated. A vertical channel housing the categorized wire-mesh porous media is numerically modeled to analyze thermal and flow characteristics of such a medium. The proposed correlations can be used in confidence to evaluate thermo-hydraulic parameters appearing in governing equations in order to numerically model various samples of stacked wire-mesh types of porous media in a variety of heat transfer applications.

Legitimacy of the Local Thermal Equilibrium Hypothesis in Porous Media: A Comprehensive Review

Local thermal equilibrium (LTE) is a frequently-employed hypothesis when analysing convection heat transfer in porous media. However, investigation of the non-equilibrium phenomenon exhibits that such hypothesis is typically not true for many circumstances such as rapid cooling or heating, and in industrial applications involving immediate transient thermal response, leading to a lack of local thermal equilibrium (LTE). Therefore, for the sake of appropriately conduct the technological process, it has become necessary to examine the validity of the LTE assumption before deciding which energy model should be used. Indeed, the legitimacy of the LTE hypothesis has been widely investigated in different applications and different modes of heat transfer, and many criteria have been developed. This paper summarises the studies that investigated this hypothesis in forced, free, and mixed convection, and presents the appropriate circumstances that can make the LTE hypothesis to be valid. For example, in forced convection, the literature shows that this hypothesis is valid for lower Darcy number, lower Reynolds number, lower Prandtl number, and/or lower solid phase thermal conductivity; however, it becomes invalid for higher effective fluid thermal conductivity and/or lower interstitial heat transfer coefficient.

Pore-scale numerical simulation of convection heat transfer in high porosity open-cell metal foam under rotating conditions

High porosity open-cell metal foam can be used in rotating machinery to improve its performances. The interstitial heat transfer coefficient is a key parameter to describe heat transfer in porous media under local thermal non-equilibrium conditions. A pore-scale numerical simulation is performed to obtain the interstitial heat transfer coefficient between air and high porosity open-cell metal foam under rotating conditions in this study. To this end, the convective heat transfer in a radially rotating channel filled with Weaire-Phelan foam cell is investigated numerically. The interstitial heat transfer coefficients are calculated at different Reynolds numbers, Rotation numbers, foam porosities and locations. And the correlation for porous-fluid interstitial heat transfer Nusselt number is established. The results show that the increasing of Reynolds and Rotation number will gradually increase the interstitial heat transfer Nusselt number. The location also has a positive effect on the interstitial heat transfer coefficient. However, the interstitial heat transfer Nusselt number gradually decreases with the increase of porosity. The established correlation can predict the interstitial heat transfer Nusselt number with a deviation within 10% at the studied ranges of the corresponding parameters. It can also be applied to the cases for larger location, larger channel size and larger Rotation number.

Macroscale Modeling of Solid–Liquid Phase Change in Metal Foam/Paraffin Composite: Effects of Paraffin Density Treatment, Thermal Dispersion, and Interstitial Heat Transfer

Abstract This work focuses on macroscale modeling of solid–liquid phase change in metal foam/paraffin composite (MFPC), addressing the treatment of paraffin density (under distinct paraffin filling conditions in metal foam), thermal dispersion effect, and influence of thermal diffusion-dominated interstitial heat transfer. To this end, a macroscale thermal non-equilibrium model for melting in MFPC with fluid convection is developed by employing the enthalpy-porosity technique and volume-averaging approach. Meanwhile, visualized experiments on the melting of the MFPC sample are carried out to validate the modeling results. Comparing the numerical modeling and experimental visualization results, it is found that for MFPC with an initially saturated filling condition in metal foam using solid paraffin, the varied paraffin density is preferred to be employed for developing accurate phase change model. However, for MFPC that can be just filled with liquid paraffin after melting (i.e., non-saturated filling condition using solid paraffin), the Boussinesq approximation is preferred to achieve satisfying phase change simulation. Thermal dispersion effect in MFPC is proved to be negligible, which should not be overvalued to avoid inducing physical distortions of heat transfer and fluid flow. Consideration of diffusion-dominated interstitial heat transfer in the thermal non-equilibrium model is vital to accurately capture phase interface evolutions as well as to reasonably simulate the mushy zone of paraffin, and the model only incorporating the convection-induced interstitial heat transfer will predict quite inaccurate phase change process. This study can provide useful guidance in macroscale modeling of phase change in MFPC associated with the thermal energy storage applications.

Improved melting of latent heat storage via porous medium and uniform Joule heat generation

To enhance the rate of heat transfer in phase change materials (PCM), high conductivity porous materials have been widely used recently as a promising method. This study introduces a novel approach for improving melting of PCM by incorporating uniform Joule heat generation with the porous structure compared to central heat generation. Different cases based on the heater-in foam configuration under the same heat generation rate are numerically verified and compared with the case of using the central heating element, which the heat transfer in the domain enhances by the porous medium. The effects of pore density and rate of heat generation are explored using the thermal non-equilibrium model to better deal with the interstitial heat transfer between the internal heat-generated-in-foam and the PCM. For the case with the central heating element, the effects of heater dimensions as well as the rate of heat generation are also investigated. The results show that the uniform heat generation from the porous structure can substantially reduce the melting time. Applying 100 kW/m3 for the rate of heat generation reduces the melting time by 21% compared with the best case of the localised heater. Meanwhile, applying higher pore-density foam does not bring any significant effect due to the uniform distribution of the heat generation. The results also show a small effect of localized heater size on the melting time with the same rate of heat generation density from the porous structure. However, for an identical volumetric heat source power of the localised heater, the rate of heat generation per volume is more effective compared with the heating element size due to the presence of the porous medium.

Flow and Thermal Transport Through Unit Cell Topologies of Cubic and Octahedron Families

Advancements in Additive Manufacturing (AM) routes have opened several opportunities for manufacturing complex porous structures which could not have been manufactured by the conventional foaming process that essentially results in unit cells represented as Tetrakaidecahedron (TKD) shape. The regular open-cell lattices belonging to the cubic and octahedron family of structures provide wide spectrum of porosity, pore-density, permeability and surface area-to-volume ratios. These complex cell topologies can potentially be manufactured additively, making the realization of above-mentioned properties possible. For efficient heat exchanger designs, the reticulated structures made from these unit cells are expected to have higher permeability, porosity, effective thermal conductivity and interstitial heat transfer coefficient. A detailed understanding of local flow and heat transport characteristics is necessary to design unit cells with such properties. To this end, four different metal foam unit cell topologies have been investigated in the present study, viz. Tetrakaidecahedron (TKD), Cube, FD-Cube and Octet. The Cube and FD-Cube unit cell topologies investigated in the present study belong to the cubic family, where the fibers are present only along the edges and face of the unit cell volume. The TKD and Octet configurations belong to the octahedron class of lattices, where complex connectivity exists within the unit cell volume. To allow for direct comparison between these three unit cells, circular fibers are chosen, which is different from the general TKD cells (tricuspid cross-sections). The porosity was fixed 0.986 which dictated the fiber dimensions of respective unit cells, with Octet fibers being thinnest. Direct simulations have been carried out with periodic boundary conditions on unit cell faces which were parallel to the flow. Such configurations when reticulated in three dimensions are representative of porous structures which are single-cell thick in the streamwise direction. These foam shapes have been proven to be very efficient as they do not allow the thermal boundary layer development. Flow and heat transfer results obtained for above boundary conditions have also been compared with the periodic boundary condition on all the faces.The direct simulation results include pressure drop per unit length and volumetric Nusselt number (corresponding to constant heat flux and constant wall temperature boundary conditions on fibers). Flow stagnation on fibers was the main contributor for both, pressure drop increase, and interstitial heat transfer enhancement. TKD unit cell had higher flow losses and thermal performance than FD-Cube. Octet (octahedron family) configuration had the highest flow losses as well as Nusselt number compared to all other unit cell topologies, because of the large surface area offered for flow stagnation.

Role of metal foam in solidification performance for a latent heat storage unit

The current latent heat storage (LHS) units are usually poor in energy charging and discharging efficiency. Given this, a two dimensional (2D) numerical model of the energy discharging process is presented and comprehensively analyzed to predict the role of metal foam in the solidification performance of LHS units. In the model, the fractal geometry reconstructed by the fractal Brownian motion is utilized for the pore characterization of the metal foam. The proposed model is validated through a melting experiment in copper foams from the reference. The temperature dynamic response and the solidification front evolution in metal foam are analyzed and compared to those in a corresponding cavity. The roles of the fractal dimension and porosity in the solidification behaviors are quantitatively analyzed. The results report that the presence of metal foam enhances the solidification performance. For the main goal of maximizing the latent storage, the appropriate porosity of an LHS unit is dependent on the duration time for the heat discharging process in the real application of thermal energy storage. Even if the porosity is the same, the fractal dimension also affects the solidification performance. A decrease in the fractal dimension (lower degree of disorder for pore distribution) provides greater access to heat flow through the phase change material-foam composite and thus leads to improvement in the interstitial heat transfer, which in turn accelerates the rate of heat release. The fractal dimension is expected to be less than 1.5 for superior solidification performance.

Heat generating porous matrix effects on Brownian motion of nanofluid

PurposeThe purpose of this study is to indicate the effect of mounting heat generating porous matrix in a close cavity on the Brownian term of CuO-water nanofluid and its impact on improving the Nusselt number.Design/methodology/approachBecause of the presence of heat source in porous matrix, couple of energy equations is solved for porous matrix and nanofluid separately. Thermal conductivity and viscosity of nanofluid were assumed to be consisting of a static component and a Brownian component that were functions of volume fraction of the nanofluid and temperature. To explain the effect of the Brownian term on the flow and heat fields, different parameters such as heat conduction ratio, interstitial heat transfer coefficient, Rayleigh number, concentration of nanoparticles and porous material porosity were investigated and compared to those of the non-Brownian solution.FindingsThe Brownian term caused the cooling of porous matrix because of rising thermal conductivity. Mounting the porous material into cavity changes the temperature distribution and increases Brownian term effect and heat transfer functionality of the nanofluid. Besides, the effect of the Brownian term was seen to be greatest at low Rayleigh number, low-porosity and small thermal conductivity of the porous matrix. It is noteworthy that because of decrement of thermal conduction in high porosities, the impact of Brownian term drops severely making it possible to obtain reliable results even in the case of neglecting Brownian term in these porosities.Originality/valueThe effect of mounting the porous matrix with internal heat generation was investigated on the improvement of variable properties of nanofluid.

Heat and Flow Characteristics of Nanofluid Flow in Porous Microchannels

In the present study, convective flow of nanofluid in porous microchannel is analyzed by utilizing field synergy principle. The effects of porous medium embedment on the field synergy of water-Al2O3 nanofluid is investigated based on locally thermal nonequilibrium model. Energy equations for both fluid and solid phases are solved analytical while the field synergy formulations based on viscous dissipative flow are developed. It is observed that the interstitial heat transfer affects the field synergy of the flow tremendously. The deviation between one-energy-equation model and two-energyequation model reduces when the field synergy of the system increases. With the embedment of porous medium, the convection performance of microchannel is enhanced due to the increased synergy between the heat and flow fields. Besides, the field synergy of the system can be further enhanced by suspending nanoparticle in conventional fluid. This study provides an auxiliary point of view on the distinctive convection performance of nanofluid flow in porous microchannel.

Simulation and Optimization of Metal-foam Tube Banks for Heat Transfer Enhancement of Exhaust Heat Exchangers

An essential issue of waste heat recovery (WHR) from engine’s exhaust gas, which could be effectively purified by modern after-treatment techniques, is the development of high-efficient, compact and lightweight high-temperature gas heat exchanger. Due to its multi-functional advantages, open-cell metal foam shows promising potentials in gas heat transfer enhancement. Thus, it is meaningful to explore the feasibility of this novel structure’s application on engine exhaust gas, by replacing bulky structures outside tubes with metal foam layers. In this paper, the heat transfer enhancement of forced convection in metal foam-wrapped tube banks was numerically studied. The Darcy-Forchheimer-Brinkman momentum model considering viscous loss and inertial loss, and the local thermal non-equilibrium energy model which considers the interstitial heat transfer between fluid and solid were employed for the porous zone. Effects of foam thickness and free stream velocity were analyzed to examine the heat transfer and pressure drop characteristics. A comparative analysis was also conducted with a bare tube bank. Results showed that the heat transfer performance of metal foam tube bank can enhance 1.8 to 2.0 times, measured in terms of the area goodness factor. In an array with fixed foam thickness, the better heat transfer performance is obtained at lower free stream velocities. It was also found that, within the designated fluid velocity range, tube banks with thicker foam layers show higher heat transfer rates and larger pressure drops as well. However, there exists an optimal dimensionless thickness of foam layer at 0.15 which gives the highest area goodness factor for the configuration considered in this study.

Direct Simulation of Interstitial Heat Transfer Coefficient Between Paraffin and High Porosity Open-Cell Metal Foam

The interstitial heat transfer coefficient (IHTC) is a key parameter in the two-energy equation model usually employed to investigate the thermal performance of high porosity open-cell metal foam/paraffin composite phase change material. Due to the existence of weak convection of liquid paraffin through metal foam during phase change process, the IHTC should be carefully determined for a low Reynolds number range (Re = 0–1), which however has been rarely addressed in the literature. In this paper, a direct simulation at foam pore scale is carried out to determine the IHTC between paraffin and metal foam at Re = 0–1. For this purpose, the cell structures reflecting realistic metal foams are first constructed based on the three-dimensional (3D) Weaire–Phelan foam cell to serve as the representative elementary volume (REV) of metal foam for direct simulation. Then, by solving the Navier–Stokes equations and energy equation for the REV, the influences of Reynolds number (Re), Prandtl number (Pr), foam porosity (ε), and pore density (PPI) on the dimensionless IHTC, i.e., the Nusselt number Nuv, are investigated. According to the numerical results, a correlation of Nuv at Re = 0–1 is proposed for metal foam/paraffin composite material, which covers both diffusion-dominated interstitial heat transfer region (Re ≤ 0.1) and convection-dominated interstitial heat transfer region (0.1 < Re ≤ 1). Finally, the applicability of this correlation in the two-energy equation model for solid–liquid phase change of paraffin in metal foam is validated by comparing the model predicted melting front with that of experimental observations made in this study. It is found that the IHTC correlation proposed in this study can be used in the two-energy equation model for well predicting the phase change process of paraffin in metal foam.

Thermal dispersion effects on heat transfer of laminar gas flow in a microtube filled with porous medium

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.

Determination of the stress jump coefficient, the interstitial heat transfer coefficient and the interface heat transfer coefficient in a porous composite system

In this work, the microscopic and macroscopic models of the porous composite system are established to study the stress jump coefficient, the interstitial heat transfer coefficient and the interface heat transfer coefficient under the local thermal non-equilibrium condition. The influences of the free fluid layer thickness, the flow types (including the Poiseuille flow, the Couette flow and the free boundary flow), the porosity and the pore diameter on the stress jump coefficient, the Biot number and the interface Biot number are discussed. In addition, an innovative method is presented to calculate the interstitial heat transfer coefficient inside the porous medium when the phenomenon of heat flux bifurcation occurs.