Computational experiments to characterize bubble formation and movement in waste glass foam layer

Computer simulation experiments are a valuable complement to physical experimentation for systems with limited access to quantities of interest. The motivation for this work is to characterize the fluid dynamic and heat transfer processes that affect melting rate of waste slurry feed during vitrification, which limits the throughput rate of the melter. The cold cap floats on the glass and consists of a reacting feed layer above a foam layer. Heat transfer to the cold cap from the molten glass below is an important factor determining melting rate. In this study, computational fluid dynamics is used to elucidate the behavior of gas-filled cavities that form underneath the cold cap in a laboratory-scale waste glass melter. The cavities are a result of coalesced gases from collapsing primary foam and air from forced convection bubblers. Bubbles in the cavity layer move horizontally with the circulation pattern of the melt and escape around the edges of the cold cap to the plenum above. The effects of varying thermophysical properties and foam parameters based on the bounds of high-level waste glass formulations were explored. Using the DAKOTA toolkit, a Latin hypercube space-filling design was used to randomly distribute samples to achieve good coverage over the parameter space with minimal points. Using the results from the set of simulations, a Gaussian process model with a linear trend was used to create response surfaces for studying cavity extent beneath the cold cap.