Numerical simulation of a secondary aluminum melting furnace heated by a plasma torch

Tests carried out in an experimental prototype of crucible melting furnace heated by a plasma torch are numerically simulated with a commercial CFD code, in order to calculate melting time, heat losses and temperature distributions in the aluminum load and refractory parts. The objective is to develop a calculating tool to assist in the design and scaling-up of industrial furnaces. Models used are 2D axisymmetric and take into account heat conduction in solid parts, convection in air and molten aluminum, interactions between gas-liquid-solid zones and radiation heat transfer. Fusion of solid aluminum is modeled with the enthalpy method. The simulation is able to predict temperatures and melting times at a reasonable computational expense. Several calculation strategies are tested concerning their computational economy and their accuracy in computing different key parameters. Results show that interactions gas-liquid-solid have an important effect. Firstly, a proper account of heat transfer and losses requires solving the conjugated problem comprising refractory walls and heated load. Secondly, thermal interaction with air cavities seems to determine the convective movement of the molten load and therefore inner-load temperature patterns and their time evolution. Nevertheless, this comprehensive simulation consumes 3.6 times the computational resources of a simplified model, where the momentum equations are not solved for the air cavity and overall furnace parameters are still reasonably predicted (e.g., with an error in fusion time less than 7.3%).