NUMERICAL ANALYSIS OF ENTROPY GENERATION IN A TWO-DIMENSIONAL POROUS HEAT RECOVERY SYSTEM

The main goal of this paper is the analysis of entropy generation in a two-dimensional porous heat recovery system. This system works based on the energy conversion between fluid enthalpy and thermal radiation. The fluid phase in this system is considered to be air assuming a non-radiative medium, whilst the solid phase is regarded as a gray radiating medium with emission, absorption, and isotropic scattering. These two phases are not in thermal equilibrium and the energy equation is separately analyzed for them. To solve the radiative equations in solid phase, the discrete ordinates method is employed. For a porous heat recovery system, the local entropy generation rate is obtained by summing the entropy generation rates due to the fluid friction and conductive and radiative heat transfer mechanisms. Besides, components of radiative entropy generation rates arise from the absorption-emission, scattering, and walls influences. However, influences of radiative parameters of optical thickness and scattering albedo on the entropy generation rates in this porous system are numerically investigated with full details. Results show that the best thermal performance of the porous heat recovery system occurs in a non-scattering medium with the highest magnitudes of optical thickness.