Analysis of fluid flow and heat transfer in a channel with staggered porous blocks

Fluid flow and heat transfer characteristics in a channel with staggered porous blocks were numerically studied in this paper. The Navier–Stokes and Brinkman–Forchheimer equations were used to model the fluid flow in the open and porous regions, respectively. Coupling of the pressure and velocity fields was resolved using the SIMPLER algorithm. The local thermal equilibrium model was adopted in the energy equation to evaluate the solid and fluid temperatures. The effect of Darcy number, Reynolds number, porous block height and width on the velocity field were studied. In addition, the effects of the above parameters as well as the thermal conductivity ratio between the porous blocks and the fluid on the local heat transfer were analyzed. The pressure drops across the channel for different cases were discussed. The results show that the flow behavior and its associated local heat transfer are sensitive to the variation of the above parameters. It is predicted by the present study that an increase in the thermal conductivity ratio between the porous blocks and the fluid results in significant enhancement of heat transfer at the locations of the porous blocks.     

Heat transfer performance analysis of a solar flat-plate collector with an integrated metal foam porous structure filled with paraffin

The analysis of energy storage process of a solar flat-plate collector with an integrated aluminum foam porous structure filled with paraffin as the phase-change medium is reported in this paper. The momentum conservation of liquid paraffin is modeled with Darcy’s law with the Brinkman–Forchheimer’s extension, while heat transfer between the metal foams and paraffin in solid and liquid phases is modeled with a two-temperature model. It is shown that the assumption of the local thermal equilibrium between the metal foams and paraffin invoked in previous studies is inappropriate in predicting the heat transfer behavior, whereas the two-temperature model proposed in this work without this assumption can more realistically predict the real-world phase-change heat transfer process in the solar collector. In particular, the numerical results indicate that the heat transfer performance can be significantly improved by using the aluminum foams filled with paraffin.     

Investigations of Heat Transfer Enhancement in a Channel with Staggered Porous Ribs by the Preconditioned Density-Based Algorithm

The preconditioned density-based algorithm and two-domain approach were used to investigate the fluid flow and heat transfer characteristics in a channel with staggered porous/solid ribs. In the porous zone, the momentum equations were formulated by the Darcy–Brinkman–Forchheimer model; and the local thermal equilibrium (LTE) model was adopted for energy equation. At the porous/fluid interface, the stress–continuity interfacial condition was utilized. The governing equations are solved by the preconditioned density-based control-volume method, with preconditioning matrix for equations of porous domain adopted, aiming to eliminate the equation stiffness of the porous seepage flow. The effects of Reynolds number, geometry parameters of ribs (rib length and thickness), and physical property of porous media (permeability and porosity) on the flow pattern and heat transfer performance were analyzed. Results indicate that, compared with that of solid ribs, the recirculating bubble behind the porous ribs is completely detached from it because of the permeability of porous media, and the size of the recirculating bubble is suppressed. The parameters that would affect the mass flow of fluid penetrating the porous ribs, including permeability, Reynolds number, baffle length and thickness, have remarkable influence on the flow pattern. All the aforementioned parameters would affect the local heat transfer performance.     

Heat transfer of phase change materials (PCMs) in porous materials

In this paper, the feasibility of using metal foams to enhance the heat transfer capability of phase change materials (PCMs) in low- and high-temperature thermal energy storage systems was assessed. Heat transfer in solid/liquid phase change of porous materials (metal foams and expanded graphite) at low and high temperatures was investigated. Organic commercial paraffin wax and inorganic calcium chloride hydrate were employed as the low-temperature materials, whereas sodium nitrate was used as the high-temperature material in the experiment. Heat transfer characteristics of these PCMs embedded with open-cell metal foams were studied. Composites of paraffin and expanded graphite with a graphite mass ratio of 3%, 6%, and 9% were developed. The heat transfer performances of these composites were tested and compared with metal foams. The results indicate that metal foams have better heat transfer performance due to their continuous inter-connected structures than expanded graphite. However, porous materials can suppress the effects of natural convection in liquid zone, particularly for PCMs with low viscosities, thereby leading to different heat transfer performances at different regimes (solid, solid/liquid, and liquid regions). This implies that porous materials do not always enhance heat transfer in every regime.     

Numerical Simulations of Fluid Flow and Heat Transfer through Aluminum and Copper Metal Foam Heat Exchanger – A Comparative Study

Abstract

This article discusses about a numerical simulation of a metal foam heat exchanger system carried out by a commercial software. A metal foam layer is attached to the bottom of the heat exchanger to absorb heat from the exhaust hot gas leaving the system. Two types of metal foams with two different pores per inch (PPI) values are considered for heat transfer enhancement. Similarly, two different materials Aluminum and copper, that poses high thermal conductivity, metal foams are considered for the present numerical simulations. The heat exchanger system is simulated over a range of 6–30?m/s fluid velocity. The proposed simulations are compared with theoretical and experimental data available in the literature. The goal is to improve the thermal performance of the heat exchanger by decreasing the pressure drop and maximizing the heat transfer rate. Finally, it has been noticed that the velocity of the fluid decreases as PPI increases at the expense of its pressure drop. The copper metal foam gives a maximum increase of 4–10% heat transfer rate compared to aluminum metal foams for a fluid velocity of 30?m/s.     

Effect of oscillatory frequency on heat transfer in metal foam heat sinks of various pore densities

In this paper, an experimental investigation was performed to study the heat transfer performance of metal foam heat sinks of different pore densities subjected to oscillating flow under various oscillatory frequencies. The variations of pressure drop and flow velocity along the kinetic Reynolds number of oscillating flow through aluminum foams were compared. The measured pressure drops, velocities and surface temperatures of oscillating flow through aluminum 10, 20 and 40 PPI foams were presented in detail. The calculated cycle-averaged local temperature and Nusselt number for different kinetic Reynolds numbers were analyzed and compared with finned heat sinks. The results of length-averaged Nusselt number for both oscillating and steady flows indicate that higher heat transfer rates can be obtained in metal foams subjected to oscillating flow. For the purpose of designing a novel heat sink using metal foam, the characteristics of the pumping power of the cooling system for aluminum foam with different pore densities were also analyzed.     

Darcy–Forchheimer flow of Ree–Eyring fluid over an inclined plate with chemical reaction: A statistical approach

In spite of various reports on non-Newtonian fluids, little is known on the impact of chemical reaction on the Darcy–Forchheimer flow of Ree–Eyring fluid when Cattaneo–Christov (C-C) heat flux (HF) is significant. The inclusion of porous medium occurs in various procedures which include heat transfer, geophysics design, and so forth. It also influences oil production recovery, energy storage units, solar receivers, and many others. The Darcy–Forchheimer flow model is important in the fields where a high flow rate effect is a common phenomenon, for instance, in petroleum engineering. In this study, we aim to analyze the dissipative Darcy–Forchheimer flow of Ree–Eyring fluid by an inclined (stretching) plate with chemical reaction. We have included the C-C HF model to investigate the heat transfer characteristics of the fluid. Equations in the mathematical model are metamorphosed as ordinary differential equations and then unriddled with the aid of shooting strategy. The main advantage of the shooting method is that it is easy to apply. The shooting method requires good initial guesses for the first derivative and can be applied to both linear and nonlinear problems. Results are explicated through graphs. We took the help of a statistical tool, that is, correlation coefficient to analyze the impression of crucial parameters on surface friction drag (skin friction coefficient), heat and mass transfer rates. The main inferences of this study are porosity parameter and Forchheimer numbers deprecate the fluid velocity, Eckert number ameliorates fluid temperature and concentration minifies with larger chemical reaction parameter. It is discovered that the Forchheimer and Weissenberg numbers deprecate the surface friction drag. Mass transfer rate has a substantial positive relationship with Schmidt number and chemical reaction. Furthermore, the heat transfer rate has a substantial positive correlation with the thermal relaxation parameter and a substantial negative correlation with the Eckert number.     

Numerical solution for Sisko nanofluid flow through stretching surface in a Darcy–Forchheimer porous medium with thermal radiation

The heat transfer assessments in a Sisko nanofluid flow over a stretching surface in a Darcy–Forchheimer porous medium with heat generation and thermal radiation are studied. The numerical analysis technique is used to assess the governing nonlinear equations of the model. The influence of Forchheimer number, porosity, heat generation, radiation, and material parameters is examined. The outlines of Nusselt number and skin friction coefficient corresponding to pertinent parameters are revealed. The comparison of Nusselt number outlines of working fluid and Newtonian fluid is depicted. From the analysis, it has been examined that with the increase in Forchheimer number and material parameter values, heat transfer function decreases, whereas heat transfer characteristics of Sisko nanofluid increase with heat generation and material parameters. Moreover, working fluid velocity outlines depreciate when there is an increase in porosity parameter for both shear-thinning and shear-thickening. The comparison of this study with previous research has been conducted.     

Advances in mathematical modeling of hydrogen adsorption and desorption in metal hydride beds with lattice Boltzmann method

This study presents numerical modeling and simulations of thermal fluid flows in high-volumetric-density metal hydride beds during hydrogen (H₂) adsorption and desorption within the lattice Boltzmann method (LBM) framework. A novel LBM is developed for predicting the flow and conjugate heat transfer in a practical lab apparatus involving a combination of solid chamber, free expansion zone, and porous media metal hydride that have not been addressed to date. With a correction term in the collision operator and a new equilibrium distribution function, the present model has a consistent expression of the heat capacity ratio for different fluid regions and derives the correct form of macroscopic energy and generalized momentum equations (including Darcy, Brinkman, and Forchheimer terms). The model is then validated through comparisons of the simulated results with previous experimental data under different initial pressure and temperature conditions for LaNi₅–H₂ storage systems as well Mg–H₂ reactors, achieving excellent agreement. In addition, accounting for conjugate heat transfer and other porous forces in the present LBM yields improved predictions over prior numerical approaches.     

金属泡沫平板结构内对流换热的数值研究

基于Brinkman-Darcy模型和两方程模型,本文对流体在金属泡沫平板通道内的强制对流换热进行了自编程数值模拟,采用体积平均法对流体在金属泡沫内的流动和换热进行宏观处理。模拟结果表明：流体主流速度随孔密度增大而减小,随孔隙率增大而增大;流体相和固体相之间的局部对流换热系数随孔隙率和孔密度增加而增加,金属泡沫对流换热性能随孔隙率增大而减小,随孔密度增大而增大。金属泡沫强化换热的效果十分明显,可以应用于需要强化换热的紧凑式换热器和散热器。     

Numerical investigation of natural convection in an inclined enclosure filled with porous medium under magnetic field

In the present study, natural convection of fluid in an inclined enclosure filled with porous medium is numerically investigated in a strong magnetic field. The physical model is heated from left-hand side vertical wall and cooled from opposing wall. Above this enclosure an electric coil is set to generate a magnetic field. The Brinkman–Forchheimer extended Darcy model is used to solve the momentum equations, and the energy equations for fluid and solid are solved with the local thermal non-equilibrium (LTNE) models. Computations are performed for a range of the Darcy number from 10⁻⁵ to 10⁻¹, the inclination angle from 0 to π/2, and magnetic force parameter γ from 0 to 100. The results show that both the magnetic force and the inclination angle have significant effect on the flow field and heat transfer in porous medium.     

A study on heat transfer enhancement using straight and twisted internal fin inserts

The present study investigated the effect of internal aluminum fins with a star-shape cross-section on the heat transfer enhancement and pressure drop in a counterflow heat exchanger. A concentric-tube heat exchanger was used with water as the working fluid. The heat transfer rate increased by 12–51% over a plain tube value, depending on internal fin configurations used. However, the pressure drop also increased substantially by 286–399%. The results showed that a straight-fin configuration is the best to produce a heat transfer increase in a counterflow heat exchanger. Twisted fin configurations did not further increase the heat transfer rate.     

Experimental and numerical study of single and two-phase flow and heat transfer in aluminum foams

This paper investigates the flow boiling characteristics of water and FC-72 in aluminum foams. For the experiments, the heat transfer processes prior to nucleate boiling, the onset of nucleate boiling and the hysteresis effect were studied. The temperature jump, marking the transition from nucleate to film boiling was observed for FC-72. Numerical simulations were performed based on water to compare with the experiments. In the single-phase simulations, the Brinkman–Forchheimer and local thermal non-equilibrium models were adopted for the momentum and energy equations, respectively while in the two-phase simulations, the two-phase mixture model was used. Comparisons between the experimental and numerical results show reasonable agreement.     

Non-thermal equilibrium model of the coupled heat and mass transfer in strong endothermic chemical reaction system of porous media

A two dimension mathematical model has been developed to simulate the coupled heat and mass transfer in a porous medium undergoing a strong endothermic chemical reaction. Differing from the traditional two phase equation model, just the temperature field of bulk flow is known from the solution of energy equation. The temperature distribution of the solid matrix is solved according to the reaction kinetics of the decomposition of calcium carbonate. The coupling of these two equations is given by the item of chemical reaction. The fluid flow is modeled by the Ergun–Forchheimer–Brinkman equation. This model is solved numerically by the alternate dimension implicit method, and the numerical results are validated by comparing with the experimental data in literature. The influence of the strongly endothermic chemical reaction on the heat and mass transfers in the porous medium is discussed. The reaction features of the packed bed of pellets are analyzed under different conditions by varying the key parameters.     

Numerical investigation of pressure drop reduction without surrendering heat transfer enhancement in partially porous channel

The present study is to investigate the numerical simulation of steady laminar forced convection in a partially porous channel, with four dissimilar porous-blocks, attached to the strip heat sources at the bottom wall. The analysis is based on the Navier–Stokes equation in the fluid field, the Darcy–Brinkman–Forchheimer flow model in the porous field, and the energy equations for two thermal fields. The effects of variations of different parameters such as porous blocks Darcy numbers, arrangements of dissimilar blocks, Forchheimer coefficient, Reynolds number, thermal conductivity and Prandtl number are investigated and the velocity and temperature fields are presented and discussed. In the dissimilar partially porous channel, it is found that when the blocks sorted from the lowest to the highest Da in the flow direction, the total heat transfer enhancement is almost the same as in the similar porous channel (Nu/Nu_sim = 92%), while the total pressure drop is considerably lower (P/P_sim = 28%). In addition, reverse arrangement of porous blocks is suggested to prepare more uniform temperature gradient in all heat sources.     

Comparison and Analysis of Heat Transfer in Aluminum Foam Using Local Thermal Equilibrium or Nonequilibrium Model

Aluminum foams are favorable in modern thermal engineering applications because of the high thermal conductivity and the large specific surface area. The present study aims to investigate an application of porous aluminum foam by using the local thermal equilibrium (LTE) and local thermal nonequilibrium (LTNE) heat transfer models. Three-dimensional simulations of laminar flow (porous foam zone), turbulent flow (open zone), and heat transfer are performed by a computational fluid dynamics approach. In addition, the Forchheimer extended Darcy's law is employed to evaluate the fluid characteristics. By comparing and analyzing the average and local Nusselt numbers, it is found that the LTNE and LTE models can reach the same Nusselt numbers inside the aluminum foam when the air velocity is high, meaning that the aluminum foam is in a thermal equilibrium state. Besides, a high interfacial heat transfer coefficient is required for the aluminum foam to reach a thermal equilibrium state as the height of the aluminum foam is reduced. This study suggests that the LTE model can be applied to predict the thermal performance at high fluid velocities or for the case with a large height.     

Assessment of the local thermal non-equilibrium condition in developing forced convection flows through fluid-saturated porous tubes

The present investigation is concerned with the numerical simulation of forced convection heat transfer flows in a tube filled with a fluid-saturated porous medium. Steady state incompressible flows with isothermal tube walls are considered along with a uniform inlet approach velocity and temperature conditions. In addition, the generalized form of the momentum equation is considered by accounting for the solid boundary and the Forchheimer quadratic inertial effects without invoking the boundary layer approximations. Moreover, the energy transport is simulated using the two-equation model, which accounts separately for the local fluid and solid temperatures. The numerical solution is obtained through the application of the finite volume method. The validity of the local thermal equilibrium (LTE) was tested over a wide domain of the employed dimensionless parameters, namely; the Peclet number, Biot-like number, effective fluid-to-solid thermal conductivity ratio, Reynolds number, Forchheimer dimensionless coefficient and Darcy number. The validity of the LTE condition was examined for the full tube length and upon excluding the first tube diameter length.     

Study on fluid–solid coupling heat transfer in fractal porous medium by lattice Boltzmann method

A lattice Boltzmann model is applied to simulate fluid–solid coupling heat transfer in fractal porous medium. The numerical simulation is conducted to investigate the influences of pressure drop and porosity on fluid flows and the effect of thermal conductivity ratio of solid matrix to fluid on heat transfer. The simulation results indicate that fluid flows still obey Darcy’s Law in the range of flow and pressure level in this paper, and that both velocity field and temperature evolution conform to the local structural characteristics of porous medium. The comparison of temperature results from lattice Boltzmann model against those from the finite-volume method (FVM, one of the conventional CFD methods) is also presented to demonstrate the reliability of LBM. The present results agree well with those from FVM, All these indicate the feasibility and the reliability for the lattice Boltzmann model to be used to reveal the phenomenon and rules of fluid–solid coupling heat transfer in complex porous structures.     

Forced Convective Heat Transfer in a Porous Plate Channel

INTRODUCTIONHeattransferenllancen1enttechniquesplayaveryimportantroleintllermalcontroltechnologies1lsedwithnlicroelectronicchips,powerfullasermirrors,aerospacecraft,thermalnuclearfusion,etc.Itiswidelyrecognizedthattl1eheattransfercanbein-creasedbyil1creasingthesurfaceareaincontactwiththecoolant.TuckermanandPease[1,2]pointedoutthatforlaminarflowinconfinedchannels,theheattransfercoefficientisinverselyproportionaltothewidthofthechannelsincethelimitingNusseltnum-berisconsta11t.Theybuiltawate…     

Significance of Dufour and Soret effects on the non-Darcy flow of Cross fluid by a tilted plate with radiation and chemical reaction: A Cattaneo–Christov heat flux model

The Darcy–Forchheimer flow model is substantial in the fields where a high flow rate effect is a common phenomenon, for instance, in petroleum engineering. In this paper, we aim to scrutinize the aspects of cross-diffusion effects on the non-Darcy flow of Cross fluid by a tilted plate with thermal radiation and chemical reaction. Metamorphosed equations are resolved with the combination of shooting and Runge–Kutta fourth-order procedures. The correlation coefficient is used to discuss the impact of pertinent parameters on friction factor and transfer rates (heat and mass). The main findings of this study are that the Dufour number escalates fluid temperature and the Soret number ameliorates the fluid concentration. It is observed that the fluid velocity minifies with the elevation in the Forchheimer number. And also, it is perceived that the heat transfer rate has a generous positive relationship with the thermal relaxation parameter. Furthermore, validation of current results with the earlier results under specified conditions is performed and an adequate concord is seen.