Three-dimensional numerical simulation of solute capillary flow of a binary mixture with a nonlinear surface tension in an annular pool*

A series simulations were performed to investigate the influence of the nonlinear surface tension on solute capillary flow of ethanol-water mixture (Sc=888) in an annular pool. The results show that when the solute capillary Reynolds number (Re_C) is small, the flow is axisymmetric and steady. When Re_C exceeds a threshold of 101, the steady flow convertes to a standing wave. A secondary flow bifurcation occurs at Re_C=484, the standing wave transforms into a traveling wave, which is characterized by propagating waves in the azimuthal direction. Compared with the thermocapillary flow of a high Pr fluid with a liner surface tension, the nonlinear surface tension has little effect on the steady flow. However, with the increase of Re_C, the surface tension concentration coefficient of the fluid near the inner cylinder is much larger than the other fluid. Therefore, the strength near the inner cylinder and flow bifurcation are respectively greater and more complicated than the thermocapillary flow. Moreover, the nonlinear surface tension promotes the flow instability.