Flow pattern transition and destabilization mechanism of thermocapillary convection for low Prandtl number fluid in a deep annular pool with surface heat dissipation

In order to understand clearly the flow pattern transition and the destabilization mechanism of thermocapillary convection for low Prandtl number fluids in a deep annular pool with surface heat dissipation, we carried out a series of three-dimensional numerical simulations by using the finite volume method. The radius ratio and the aspect ratio of an annular pool are respectively fixed at 0.5 and 1.0. Prandtl number of the working fluid is 0.011. Because the total heat dissipation coefficient on the free surface for low Prandtl fluids is small, Biot number is varied from 0 to 1.0. Results indicate that thermocapillary convection experiences the transitions from axisymmetric steady state flow into three-dimensional steady flow, and then into three-dimensional oscillation flow with the increase of Marangoni number. The critical Marangoni number of flow pattern transition decreases slightly with the increase of Biot number, and the maximum temperature and velocity fluctuations appear near the lower part of outer wall. The azimuthal temperature fluctuation on the free surface gradually shrinks to the inner wall, and the temperature fluctuation region decreases. However, it remains almost unchanged near the bottom of the annular pool, but the fluctuation amplitude increases.