Radiative and conductive heat transfer in a quiescent gas‐solid bed of particles: Theory and experiment

This paper concerns a study of radiation as a contributing mechanism in the transfer of heat between discrete solid particles. A theory for transfer in such systems is generalized to include planar‐, spherical‐, and cylindrical‐bed geometries; because of the particulate nature of the system the generalization is given in terms of finite‐difference equations. Transfer experiments were performed in a quiescent cylindrical bed with an axial heat source and a cylinderical containing‐wall sink. Heat fluxes and radial‐temperature profiles were measured. As the experiments were arranged, only modest temprature gradients were established between source and sink, but the ambient sink temperature was taken in steps from 100° to 1,000°C. For a bed of 3.8‐mm.‐diameter alumina spheres the ratio of heat transferred by radiation to that transferred by conduction was estimated to increase with average bed temperature from the order of 0.1 at 100°C., to 1.2 at 1,000°C. The effects of temperature on bed reflectivity and transmissivity and on apparent boundary‐temperature discontinuities are discussed.