Numerical Study of Turbulent Heat Transfer Above a Porous Wall

This study is concerned with mixed convection heat transfer through porous media; involved (among others) in geothermal energy technology, high performance insulation for building, cold storage, and energy efficient drying processes. Mixed convection in a vertical porous rectangular channel is studied numerically. The study is based upon the extended Darcy -Forchheimer -Brinkman model, taking the effect of viscous and inertial forces into account. Two opposite sides of the rectangular channel serve as heat source and heat sink. The other two sides serve as adiabatic walls. The working fluid enters the packed channel at a uniform velocity, and flows against gravity through homogeneous spherical beads. Its temperature at the inlet is maintained at a temperature between the heat source and heat sink temperatures. The macroscopic equations governing such type of flow are derived according to the volume averaging technique and then made non-dimensional. Numerical solution of the model is achieved by the finite volume method and the results are compared with those obtained by Pu et al . Both sets of results show a good agreement, which implies present model validity. The velocity and temperature fields are determined for various porous parameters, Peclet number, Pe, and modified Rayleigh number, Ra*. Nusselt number at the walls is also determined. It seems to depend on two dimensionless parameters; a mixed convection parameter, λ, and the Peclet number, Pe.

Journal of Fluids Engineering-transactions of The Asme, 1995

A new model of turbulent flow and of two-temperature heat transfer in a highly porous medium is evaluated numerically for a layer of regular packed particles. The layer can have heat exchange from the defining surfaces. The commonly used models of variable morphology functions for porosity and specific surface were used to obtain comparisons with other works in a relatevly high Reynolds number range. A few outstanding features of the closure models for additional integral terms in equations of flow and heat transfer are advanced. Closures were developed for capillary and globular medium morphology models. It is shown that the approach taken to close the integral resistance terms in the momentum equation for a regular structure can be obtained in a way that allows the second order terms for laminar and turbulent regimes to naturally occur. These terms are taken to be close to the Darcy term or Forchheimer terms for different flow velocities. The two-temperature model was compared with a onetemperature model using thermal diffusivity coefficients and effective coefficients from various authors. Calculated pressure drop along a layer showed very good agreement with experiment for a porous structure of spherical beads. A simplified model with constant coefficients was compared with analytical solutions. < -kinematic viscosity [m 2 /s] D density [kg/m 3 ] D 0 -reference density [kg/m 3 ] J turbulent friction stress tensor [N/m 2 ] J w -wall shear stress [N/m 2 ]

Journal of Porous Media, 2012

Convective heat transfer in a vertical porous channel heated by the wall and isolated on the other face was simulated numerically and experimentally. The porous medium is formed by a solid matrix of spherical beads. The considered fluid is air that saturates the solid matrix. The two-temperature model and the Darcy-Brinkman-Forchheimer equation are adopted to represent this system and the porosity is considered as variable in the domain. The numerical model was used to analyze the effect of several operating parameters on heat transfer enhancement. Heat transfer decreases with the increase of the form factor. When Biot number increases, heat transfer between the heated wall and the porous domain is increased. Heat transfer increases with Reynolds

Drying Technology, 2009

The heat transfer between a forced flow of a pure fluid phase and a porous medium is theoretically studied. A unified enthalpy model is used to investigate the transient temperature field in the pure fluid phase and in the porous medium. Possible transition from saturated to nonsaturated porous medium is considered. From the temperature field obtained, the time variation of the local temperature and convective heat transfer coefficient at the interface porous-pure fluid regions are studied. Numerical results provide also the parametric information concerning effects of the thickness of the porous layer on theses parameters at the transient and the steady regimes.

Heat Transfer Engineering, 2012

The heat transfer characteristics of the flow around rectangular cylinders having various aspect ratios with uniform injection or suction through the rear, top, bottom, and all surfaces have been studied numerically. The effects of injection or suction on heat transfer have been linked to the analysis via wall functions of the velocity and temperature sublayers. The computational code employed in the present study was verified with a typical benchmark problem of the flow around a square cylinder. The results show that the heat transfer between the main flow and rectangular cylinders is substantially influenced by injection or suction-that is, suction enhances the heat transfer, while injection through the rear surface provides some thermal protection.

International Information and Engineering Technology Association, 2018

A numerical investigation is presented to illustrate the impact of aspect ratio in a conjugate heat transfer enclosure filled with porous media and partially heated from vertical walls. The left and right walls are partially heated and cooled, respectively. The remaining partitions of the vertical walls in addition to the top and bottom walls are considered to be adiabatic. the present work is limited to two different cases: Top-Bottom (case 1) and Bottom-Top (case 2). The dimensionless Navier-Stokes governing equations are solved using the finite element method. The parameters of interest are the modified Rayleigh number 10 ≤ Ra ≤ 10 3 , the finite wall thickness 0.02 ≤ D ≤ 0.5, 0.1 ≤ Kr ≤ 10 and the aspect ratio 0.5 ≤ A ≤ 10. The results are presented in term of streamlines, isotherms and average Nusselt number for fluid phase and along the solid hot wall. The results indicated that the locations of partially active walls have great influence on heat transfer rate. I was shown that Bottom-Top arrangement gives better heat transfer rate compared to that of Top-Bottom. It was also found that by increasing the Rayleigh number, the rate of heat transfer increased. In contrast, increasing the wall thickness and aspect ratio reduced the heat transfer rate.

Journal of University of Babylon for Engineering Sciences, 2019

This work presents experimental investigation of flow and heat transfer characteristics for entry length of turbulent flow in a rectangular duct fitted with porous media and air as the working fluid. Rectangular duct (300×30 mm) with a hydraulic diameter (54.54 mm) was subjected to constant heat flux from lower surface (1.5 ×10 2-1.8 ×10 2 w/m 2) and Reynolds number ranged (3.3x10 4 up to 4.8x10 4). Copper mesh inserts (as porous media) with screen diameter (54.5 mm) for vary distance between two adjacent screens of (10 mm), (15 mm) and (20 mm) in the porosity range of (0.98-0.99) are considered for experimentation. The effect of porous height ratio (full and partial) are also considered. It is observed that the enhancement of heat transfer by using mesh inserts when compared to a plain surface is more by a factor of (2.2) times where the skin fraction coefficient is about (5) times. An Empirical correlation for Nusselt number and friction factor are developed for the mesh inserts from the obtained results.

Transport in Porous Media, 2010

Steady and pulsatile flow and heat transfer in a channel lined with two porous layers subject to constant wall heat flux under local thermal non-equilibrium (LTNE) condition is numerically investigated. To do this, a physical boundary condition in the interface of porous media and clear region of the channel is derived. The objective of this work is, first, to assess the effects of local solid-to-fluid heat transfer (a criterion indicating on departure from local thermal equilibrium (LTE) condition), solid-to-fluid thermal conductivity ratio and porous layer thickness on convective heat transfer in steady condition inside a channel partially filled with porous media; second, to examine the impact of pulsatile flow on heat transfer in the same channel. The effects of LTNE condition and thermal conductivity ratio in pulsatile flow are also briefly discussed. It is observed that Nusselt number inside the channel increases when the problem is tending to LTE condition. Therefore, careless consideration of LTE may lead to overestimation of heat transfer. Solid-to-fluid thermal conductivity ratio is also shown to enhance heat transfer in constant porous media thickness. It is also revealed that an increase in the amplitude of pulsation may result in enhancement of Nusselt number, while Nusselt number has a minimum in a certain frequency for each value of amplitude.

Transport in Porous Media, 2011

Conjugate natural convection-conduction heat transfer in a square porous enclosure with a finite-wall thickness is studied numerically in this article. The bottom wall is heated and the upper wall is cooled while the verticals walls are kept adiabatic. The Darcy model is used in the mathematical formulation for the porous layer and the COMSOL Multiphysics software is applied to solve the dimensionless governing equations. The governing parameters considered are the Rayleigh number (100 ≤ Ra ≤ 1000), the wall to porous thermal conductivity ratio (0.44 ≤ K r ≤ 9.90) and the ratio of wall thickness to its height (0.02 ≤ D ≤ 0.4). The results are presented to show the effect of these parameters on the heat transfer and fluid flow characteristics. It is found that the number of contrarotative cells and the strength circulation of each cell can be controlled by the thickness of the bottom wall, the thermal conductivity ratio and the Rayleigh number. It is also observed that increasing either the Rayleigh number or the thermal conductivity ratio or both, and decreasing the thickness of the bounded wall can increase the average Nusselt number for the porous enclosure.

2010

Abstract—The laminar field and heat transfer enhancement of forced convection in various counterflow porous channels with a joint aluminum plate was studied, using control volume technique and SIMPLE procedure for the velocity-pressure Coupling. Hydrodynamic and heat transfer results are reported for three configurations:(1) nonporous channels (NPC)(2) both channels filled by porous structure (BPC), and (3) only the channel contains hot fluid, filled by porous structure and other one is nonporous (HPC).