Studies on macrosegregation and double diffusive convection during directional solidification of binary mixture

Experimental and numerical studies on macrosegregation during directional solidification of an aqueous ammonium chloride solution in a rectangular cavity are presented. Depending on the initial concentration and boundary temperature conditions, three distinct situations in the liquid during the solidification process are studied: mass diffusion only, solutal convection and double diffusive convection. The time dependent concentration of the solution inside the cavity is measured online for the above three situations using a laser based technique. This technique measures refractive index of the solution, which indirectly gives the concentration variation at a point in the solution during solidification. The interface growth is photographed using a shadowgraph technique, and the flow is visualised using a sheet of laser light scattered by neutrally buoyant, hollow glass spheres seeded in the fluid. Corresponding numerical studies are performed using a macroscopic model based on a fixed grid, enthalpy based, control volume approach. A good agreement between the experimental and computational results is observed