Computational modeling of temperature, flow, and crystallization of mold slag during double hot thermocouple technique experiments

A three-dimensional finite-difference model has been developed to study heat transfer, fluid flow, and isothermal crystallization of mold slag during double hot thermocouple technique (DHTT) experiments. During the preheating stage, temperature in the middle of the mold slag sample was found to be significantly [∼350 K (∼77 °C)] lower than near the two thermocouples. During the quenching stage, the mold slag temperature decreases with the cooled thermocouple. The temperature across the mold slag achieves a steady, nonlinear temperature profile during the holding stage; the insulating effect of the crystallizing layer in the middle of the slag sample causes the high temperature region to become hotter, while the lower temperature mold slag becomes cooler. Fluid flow is driven by Marangoni forces along the mold slag surface from the hotter region to the cooler region, and then recirculates back through the interior. Slag velocities reach 7 mm/s. Crystallization is predicted to start in the middle of the slag sample first and then grows toward both thermocouples, which matches well with observations of the DHTT experiment.