Onset of convection in a porous mush during binary solidification

The onset of convection in a mushy layer during solidification of a binary melt is investigated by using the propagation theory we have developed. The critical conditions for the mushy-layer-mode of instability are obtained numerically for aqueous ammonium chloride solution. The mush thickness at the onset of convection is predicted as a function of the solution viscosity and compared with the experimental data. The onset time of the mushy-layer-mode convection has a minimum point with varying the superheat. When the superheat is large, the mushy layer grows slowly and a long time is required for the onset of convection.