ONSET OF OSCILLATORY CONVECTION IN BINARY-MIXTURES WITH SORET EFFECTSAND SOLIDIFICATION

The oscillatory instability of convection in a binary liquid-mixture w ith negative Soret effects coupling Benard convection and solidificati on is investigated when the temperature of the upper boundary is below the freezing point of the two-component system. Complete rejection of the lean component from the solid into the liquid phase is assumed. T he Soret coefficient and the coefficients of thermal and solutal expan sion depend strongly on the local concentration in the liquid and, con sequently, on the thickness of the solidified layer. Linear stability analysis for typical ethanol-water mixtures demonstrates that the vari ation of concentration is a dominant effect in the destabilization of the conductive state.