Influence of Natural Convection on Melt Shape During In Situ Vitrification

A study of natural convection during In Situ Vitrification (ISV) is presented. ISV is a hazardous waste remediation process in which contaminated soil and/or buried waste is treated in place by direct application of electrical power to the contaminated region via submerged electrodes. The magnitude of the resulting electrical resistance heating is sufficient to cause soil melting. As the molten region grows, natural convection motion of the molten soil occurs. This paper presents numerical results obtained by considering natural convection melting when solving the strongly coupled momentum and energy equations using finite element methods. A local heat source is calculated by solving the electric field equation and calculating a Joule Heat source term. Melt shapes obtained from runs with various values of the coefficient of volume expansion (β) in the buoyancy terms of the momentum equations are presented. Results of a pure conduction model are also presented. The melt fronts calculated from the fluid flow model melt more uniformly downward, whereas the melt front from the conduction model melts faster in the center and slower near the electrodes. Melt volumes for all models are approximately the same for a specified time period.