A numerical model of convective effects in diffusion dominated directional solidification of a metal analogue (NH4Cl-H2O) at one gravity and microgravity

A numerical model is developed to simulate the directional solidification of a dendritic metal analogue material, ammonium chloride and water, in support of a planned series of microgravity experiments. The model is first validated by comparison with ground-based data. Undercooling (non-equilibrium) effects are shown to be significant. The one-gravity computations correlate well with the ground-based data for the initial diffusion limited growth and the transition to dominant convective flows at a critical solutal and thermal Rayleigh number. The model is then used to predict the directional dendritic solidification for a sample low gravity run and the results are compared with one-gravity data.