Convection in Binary Mixures with Negative Soret Effect

Double diffusive convection in a cubic cell filled with a binary mixture of water and isopropanol is numerically analyzed. The system is heated from above while the Soret coefficient, i.e. thermodiffusion, is negative. Negative Soret effect corresponds to component separation in binary mixtures with the denser component migrating to the hot wall. In the case of heating from above density stratification is stable in a pure liquid. However in the case of a binary mixture with negative Soret effect unstable density stratification is established in the system. Due to negative Soret effect the heavier liquid is accumulated on the top of the lighter one. At some moment this unstable stratification leads to the appearing of motion in the liquid volume. 3D numerical simulations of the non-linear time-dependent Navier-Stokes, heat and mass transfer equations were performed. The parameters of the system correspond to a realistic binary mixture enabling comparison of theoretical predictions with planned experimental studies; Schmidt and Prandtl numbers are Sc=1620, Pr=10.85. The development of fluid motion in space and time is analyzed to identify the underlying physical mechanisms leading to instability.