Fluid‐particle heat transfer in packed beds

Abstract Steady state heat transfer experiments were carried out in a 4‐in. I.D. transite tube packed with 3/8‐, 1/4‐, and 5/32‐in. steel spheres. Heat was generated in the pellets by means of a high‐frequency induction coil surrounding the test section. Average heat transfer coefficients between the bed of spheres and a stream of air passing through the bed were calculated for Reynolds numbers of from 200 to 10,400. To ensure the reproducibility of the data, the bed was repacked six times for each pellet size. A study of the effect of the tube‐to‐pellet‐diameter ratio indicates that this effect is large for low values of the ratio, but much smaller for higher ratios. The results are presented both graphically and in terms of empirical equations. The analogies among heat, mass, and momentum transfer are discussed, and it was found that no simple relation between the heat transfer coefficient and the friction factor exists for packed beds with a gas as the fluid. An attempt is made to predict the heat transfer rates for packed beds from heat transfer data for single spheres and from pressure‐drop measurements for the packed bed; however, the rates predicted from the pressure‐drop measurements are somewhat lower than the experimental results.