Natural Convection Heat Transfer in Beds of Inductively Heated Particles

Experimental observations of the onset of convective motion in beds of inductively heated particles have been made. Data for the heat transfer coefficient were obtained from water-cooled beds of steel particles. The particulate beds were formed in a 10.4 cm dia glass jar, insulated at the bottom and on the sides. The free surface of a layer of water overlying the bed was maintained at a constant temperature by a copper plate cooled with tap water. In the experiments, the depths of the particulate bed and the overlying layer were varied. The observations showed that increasing the depth of the liquid layer over the bed tended to lower the critical internal Rayleigh number at which the onset of convection occurred. For overlying liquid layer-to-bed depth ratios of one or more, natural convection was observed to begin at R₁ ≃ 11.5. The heat transfer data for R_I > 11.5 are correlated with Nu = 0.190 R_I^0.69 However, with no liquid layer on top of the bed, natural convection was observed to occur at R_I ≃ 46, which is slightly higher than observed in earlier studies made with Joule heating.