Stability of ternary and binary mixtures in a vertical slot including the Soret effect.

Convective instabilities in a vertical slot containing a single fluid are longitudinal if side heated and transverse in the presence of an adverse density gradient. Here we examine the influence of the concentration field generated by thermodiffusion in ternary and binary mixtures of otherwise uniform concentrations on these phenomena at parameter values of available experiments. In a binary mixture, a lighter component with positive separation ratio epsilon migrates to the hot wall, which augments thermal buoyancy enhancing instability. It is also convected upwards and the resulting stable stratification enhances stability. The preferred instability in this case is the longitudinal mode. When epsilon<0 thermal buoyancy is opposed, unstable stratification is created, and long unstable transverse modes prevail. This is also generally true for a ternary mixture when both the separation ratios of the two lighter components are negative or positive, and either scenario may hold when they assume opposite signs, depending on four diffusion and two concentration expansion coefficients.