Transient heat transfer characteristics of an energy recovery system using a porous medium

Abstract

The transient heat transfer characteristics of an obstructing porous layer and its significant role as an effective radiative converter are analysed in this work. A basic high-temperature flow system is considered in which hot non-radiating gas flows through a homogeneous porous medium. The porous medium, in addition to its convective heat exchange with the gas, may absorb, emit, and scatter thermal radiation. It is desirable to have a large amount of radiative heat flux from the porous layer in the upstream direction (toward the system). Convection and radiation are assumed to take place simultaneously in the porous medium. In order to analyse the thermal characteristics of the porous layer, the coupled energy equations for the gas and porous medium based on a two-flux radiation model are solved numerically. The numerical simulation of the heat transfer process in the system is provide by utilization of the Crank-Nicolson method. It is found that in the initial period, the porous layer acts as an almost perfect insulator and operates efficiently to recover the energy that would otherwise be wasted. In the limited case of no scattering, the present results are compared with the reported theoretical results and also with the experimental data and good agreement is found.