Simulation of Slag Freeze Layer Formation: Part II: Numerical Model

The experiments from Part I with CaCl2-H2O solidification in a differentially heated, square cavity were simulated in two dimensions using a control volume technique in a fixed grid. The test conditions and physical properties of the fluid resulted in Prandtl and Rayleigh numbers in the range of 50 and 2.1 × 108, respectively, and the solidification was observed to be planar with dispersed solid particles. In the mathematical model, temperature-dependent viscosity and density functions were employed. To suppress velocities in the solid phase, various models were tested, and a high effective viscosity was found most appropriate. The results compare well with the experiments in terms of solid layer growth, horizontal and vertical velocities, heat transfer coefficients, and temperature distributions. Hydrodynamic boundary layers on the solidified front and on the hot vertical wall tend to be nonsymmetric, as well on the top and bottom adiabatic walls. The high viscosity value imposed on the two-phase zone affects the velocity profile close to the solid front and modifies the heat transfer rate.