Numerical Simulation of Thermocapillary Flow Induced by Non-Uniform Evaporation on the Meniscus in Capillary Tubes

Three-dimensional numerical simulation was developed to investigate thermocapillary flow induced by non-uniform evaporation on the meniscus in capillary tubes. Capillary tube radiuses ranging from 0.1 to 1 mm were considered and the working liquid was methanol. The effects of tube size, evaporation heat flux and buoyancy on thermocapillary flow were investigated. The results show that the non-uniform evaporation on the meniscus leads to two opposite temperature gradients along the radial direction, which generate two thermocapillary flow vortexes under the meniscus. For horizontal capillary tubes with r(0) >= 0.32 mm, the path-lines in the vertical center plane are asymmetrical, which is attributed to the combined buoyancy and thermocapillary effects. For the vertical capillary tube, with increasing average evaporation heat flux, the steady axisymmetrical flow will gradually transit to a steady asymmetrical flow and eventually becomes a three-dimensional oscillatory flow.