A.A. Mohamad

Combustion in porous media and its applications – A comprehensive survey

The rapid advances in technology and improved living standard of the society necessitate abundant use of fossil fuels which poses two major challenges to any nation. One is fast depletion of fossil fuel resources; the other is environmental pollution. The porous medium combustion (PMC) has proved to be one of the technically and economically feasible options to tackle the aforesaid problems to a remarkable extent. PMC has interesting advantages compared with free flame combustion due to the higher burning rates, the increased power dynamic range, the extension of the lean flammability limits, and the low emissions of pollutants. This article provides a comprehensive picture of the global scenario of research and developments in PMC and its applications that enable a researcher to decide the direction of further investigation. The works published so far in this area are reviewed, classified according to their objectives and presented in an organized manner with general conclusions. A separate section is devoted for the numerical modeling of PMC.

Non-Darcy effects in buoyancy driven flows in an enclosure filled with vertically layered porous media

Abstract Natural convection in an enclosure filled with two layers of porous media is investigated numerically. Constant heat flux is imposed on the left vertical wall and the right wall is assumed to be at a low temperature. The focus of the work is on the validity of the Darcy model when various combinations of fluid Rayleigh number, Darcy number and permeability ratios are considered for fixed values of the modified Rayleigh numbers. It is found that the boundary effects (Brinkman term) have significant importance at higher modified Rayleigh numbers (Rayleigh number based on permeability, Ra m ). Calculations are performed for a modified Rayleigh number up to 10 5 . The results showed that, for the investigated range of parameters, the flow structure and heat transfer could be different than what Darcy model predicts. Two circulations are predicted for Ra f =1×10 8 , for two different cases, Da =1×10 −3 , K r =1000 and Da =1×10 −4 , K r =100 ( K r = K 1 / K 2 ). For K r >1, increasing permeability ratio decreases flow penetration from layer 1 to layer 2 while reverse is true for K r Ra m ( Ra m ⩽10 3 ) and K r =1000, the heat transfer is conductive in the right layer, while this is true for the left layer for K r =0.001. It is possible to obtain no-slip velocity boundary conditions both at the walls and at the interface between the porous layers even for very low permeability.

Experimental Investigation of the Potential of Metallic Porous Inserts in Enhancing Forced Convective Heat Transfer

We investigate the effect of a metallic porous matrix, inserted in a pipe, on the rule of heal transfer. The pipe is subjected to a constant and uniform heat flux. The effects of porosity and thickness of the porous matrix on the heat transfer rate and pressure drop are investigated. That is, the surface temperature distribution along a heated section of the pipe, the pressure drop over this section, as well as the inlet temperature of the air were continuously monitored with a data acquisition system and recorded when steady-sale conditions were attained. The results obtained for a range of Reynolds numbers 1000-4500, comprise both laminar and turbulent regime

Double diffusive convection in a vertical enclosure inserted with two saturated porous layers confining a fluid layer

Abstract Thermosolutal natural convection in an enclosure filled with fluid and inserted with isotropic or anisotropic porous layers is analyzed numerically. Identical porous layers are attached to the vertical walls, and the walls are held at constant temperatures and concentrations. The horizontal walls of the enclosure are assumed to be adiabatic and impermeable. The aspect ratio of the cavity is equal to two and the saturating fluid is air ( Pr =0.71). The analysis is performed for thermal Grashof numbers 10 6 and 10 7 , Schmidt number of 7.1 and for different Darcy number, porous layer thickness and permeability ratio. The results are presented for thermally driven flow, N =0, and for concentration driven flow, N =10. The effect of hydraulic anisotropy on the rate of heat and mass transfer is discussed. It is found that the rate of heat transfer and the rate of mass transfer are weak functions of the Darcy number for high and low permeability regimes. For a certain range of the parameters, the rate of heat transfer decreases when the flow penetrates into the porous layer. Hence, there is an optimum (minimum) value of Nusselt number, which is a function of the anisotropy parameter. Correlation for heat and mass transfer are presented.

Double diffusion, natural convection in an enclosure filled with saturated porous medium subjected to cross gradients; stably stratified fluid

Abstract Two- and three-dimensional flows, heat and mass transfer in a horizontal enclosure with aspect ratio of two filled with saturated porous medium were analyzed numerically. The enclosure is heated differentially and stably stratified species concentration is imposed vertically. The Prandtl number is fixed to 10 (aqueous solutions). The Lewis number is varied in the range of 1.0–1000 to cover a wide range of species diffusion material in water. The work is concentrated on stable stratified flow. The results of two- and three-dimensional models were compared. Interesting results are obtained for a wide range of solutal to thermal buoyancy ratios. The difference in the rate of heat and mass transfer between prediction of three- and two-dimensional simulations is not that significant, even though the flow exhibits a three-dimensional structure. This is due to the fact that the spanwise flow is very weak when compared with main flow.

Transient natural convection in an enclosure with horizontal temperature and vertical solutal gradients

Abstract Transient, double diffusive natural convection in a horizontal enclosure is investigated numerically and analytically. The enclosure is heated and cooled along the vertical walls and solutal gradient is imposed vertically. The objective of the work is to identify the flow regime for thermal and solutal dominated flows. It is found that the flow becomes unstable (oscillatory) for finite range of solutal to thermal buoyancy ratios. It is possible to obtain different solutions on this region depending on the initial conditions. Also, the results reveal that the thermal convection may be suppressed for strongly stratified fluid. Owing to the large number of parameters, the results are reported for aspect ratio of two, Prandtl number of 7.0 (water) and Lewis number of 100 (aqueous solution). Rayleigh number is varied between 7×103 and 7×105.

Natural convection in a confined saturated porous medium with horizontal temperature and vertical solutal gradients

Abstract Double-diffusive natural convection in a horizontal enclosure filled with saturated porous medium is investigated numerically. Brinkman extension of Darcy model is adopted in the analysis. The enclosure is heated and cooled along vertical walls and solutal gradient is imposed vertically. The objective of the work is to understand the physics of the flow and to identify the flow regimes for thermal and solutal dominated flows. Since the number of parameters is large, the results are reported for an aspect ratio of two, Prandtl number of 0.71 (air) and Lewis number of 10 (hydrocarbon fuel). Grashof and Darcy numbers may vary between 10 6 –10 8 and 10 −4 –10 −6 , respectively. It is found that the flow becomes unstable for finite range of solutal-to-thermal buoyancy ratio and it is possible to obtain different solutions in this region, depending on the initial condition. Funnel-type channelling flow is predicted along the vertical boundaries for thermally driven flow. Also, for thermally driven flow, concentration reversal is possible due to the thermal advection mechanism. Strong stratified fluid may suppress the thermal convection and heat transfer becomes conductive.

Natural convection in a porous cavity with spatial sidewall temperature variation

Purpose – To study the natural convention in a square porous cavity induced by heating one of the sidewalls and the other sidewall is cooled, while the horizontal walls are adiabatic. The heated wall is assumed to have spatial sinusoidal temperature variations about a constant mean value.Design/methodology/approach – The Darcy model is used in the mathematical modeling of the natural convection in porous cavity. A finite volume method based on QUICK scheme is used to solve numerically the non‐dimensional governing equations.Findings – It is found that the average Nusselt number varies based on the hot wall temperature. It increases with an increase in the amplitude, while the maximum average Nusselt number occurs at the wave number of k=0.75 for Rayleigh number based on the permeability of the medium of 500 and 1000 and at k=0.70 for a Rayleigh number of 10‐200.Research limitations/implications – The effects of the amplitude (0‐1.0) and the wave number (0‐5) of the heated sidewall temperature variation on...

Enhanced Heat Transfer Using Porous Carbon Foam in Cross Flow—Part I: Forced Convection

Cogeneration of heat and power has become standard practice for many industrial processes. Research to reduce the thermal resistance in heat exchangers at the gas/solid interface can lead to greater energy efficiency and resource conservation. The main objective of this experimental study is to quantify and compare the heat transfer enhancement of carbon foam and aluminum fins. The study measures the heat transfer rate and pressure drop from a heated vertical pipe, with and without porous medium, in forced convection. The largest increase in Nusselt number was achieved by aluminum fins, which was about three times greater than the best carbon foam case.

Natural Convection Heat Transfer Enhancements From a Cylinder Using Porous Carbon Foam: Experimental Study

The main objective of this experimental study is to quantify and compare the heat transfer enhancement of carbon foam and aluminum fins in natural convection. The study measures steady state heat transfer from a heated vertical pipe, with and without porous medium. The largest increase in Nusselt number was achieved by a solid carbon foam sleeve, which was about 2.5 times greater than a bare copper pipe.