Experiments on the Role of Natural Convection in the Melting of Solids

Abstract

Experiments are performed whose results convey strong evidence of the dominant role played by natural convection in the melting of a solid due to an embedded heat source. The research encompassed both melting experiments and supplementary natural convection experiments, with a horizontal cylinder as the heat source. For the melting studies, the cylinder was embedded in a solid at its fusion temperature, whereas in the natural convection tests it was situated in the liquid phase of the same solid. A special feature of the experiments was the use of a grid of approximately 100 thermocouples to sense thermal events within the phase change medium. The time history of the heat transfer coefficients for melting was characterized by an initial sharp decrease followed by the attainment of a minimum and then a rise which ultimately led to a steady value. This is in sharp contrast to the monotonic decrease that is predicted by a pure conduction model. The steady state values were found to differ only slightly from those measured for pure natural convection. This finding enables melting coefficients to be taken from results for natural convection. The positions of the solid-liquid interface at successive times during the melting process also demonstrated the strong influence of natural convection. These interfaces showed that melting primarily occurred above the cylinder. In contrast, the interfaces given by the conduction model are concentric circles centered about the cylinder.