NUMERICAL ANALYSIS OF BINARY SOLID-LIQUID PHASE CHANGE WITH BUOYANCY AND SURFACE TENSION DRIVEN CONVECTION

Abstract

The effects of thermo/diffusocapillary convection on the solidification of aqueous NH₄Cl in a rectangular cavity have been simulated numerically using a newly developed continuum model. Diffusocaptttary convection is negligible relative to thermocapillary convection, and for a 20 × 20 mm cavity in a one-gravity environment, thermocapillary effects are most pronounced during the early stages of solidification, when flow conditions are characterized by three major cells. One cell, driven by solutal buoyancy forces, extends from the mushy region to the melt and separates top and bottom melt region cells driven primarily by surface tension and buoyancy forces, respectively. With increasing time, however, the top cell strengthens and eventually envelops the entire melt. In terms of the strength of the flow, the liquidus front morphology, and the amount of solid formed, final conditions differ only slightly from those predicted for pure thermal/solutal convection.