UNSTATIONARY COUPLED HEAT-TRANSFER WITHIN A NON ISOTROPIC SCATTERING POROUS-MEDIUM HEATED BY RADIATION

This paper presents the results of a theoretical one-dimensional study of heat transfer inside a fixed bed, the front surface of which being heated by radiation, a cold gas flowing through. The aim of this stud y is to show the effects of radiation on the transient temperature pro files in both the solid and the gas phases. The solid phase is suppose d to be a continuous, absorbing, scattering and participating semi-tra nsparent medium. A discrete ordinate method is used for the radiative transfer calculation, and a fast algorithm allowing analysis of the ge neral problem of scattering, the spatial variation of optical properti es and different kinds of boundary conditions, is presented. In order to make move general conclusions, the dimensionless problem is formula ted with the Planck's number N (conduction-radiation pur ratio), the B oltzmann's number Bo (convection-radiation pur ratio) and other charac teristic numbers. The results of our study are compared with previous literature values. It is mainly shown that N influences the temperatur e gradient in the vicinity of the heat source, whereas Bo controls the temperature level in the remote zone. The study of the transient regi me revealed some unexpected dynamic phenomena as a function of charact eristic exchange time, in particular the temperature inversion between solid and gas phases.