A Study of Scrap Heating by Burners: Part II—Numerical Modeling

A computational fluid dynamics code was developed to model the heating of a bed of porous steel scrap by combustion gases from a burner. The code accounted for nonuniform void fraction in the bed; turbulent, non-Darcian flow, heat transfer from the gas to the scrap; and radiation. The measured bed porosity values were used in the code. Because steel scrap pieces are very irregular in shape and size, the effective particle diameter was fitted to measurements made in a 1-m3 capacity furnace, as reported in part I. It was found that the lower porosity of the scrap was the most beneficial in increasing the efficiency of heat transfer to the scrap bed because the interfacial area is larger. The effect of particle size was much smaller. It was found that the configurations that increased the residence time or path length of the gases increased the efficiency. The measured porosity of the bed approached unity at the walls, so this provided an easy path for the gas to short-circuit the bed, which limited the effectiveness of decreasing the porosity to increase heat-transfer efficiency. Similarly, simulations of nonuniform scrap distributions reduced efficiency of heat transfer due to short circuiting. The implications of the findings for industrial operations are discussed.