THERMOCAPILLARY CONVECTION WITHIN SHORT-DURATION PULSE-HEATED LIQUID DROPLETS

Abstract

Thermocapillary-driven convection within short-duration pulse-heated liquid droplets was studied computationally. The phenomenon is governed by the dimensionless parameters of the surface-tension Reynolds number Re, the Prandtl number Pr, and the Biot number Bi. Critical surface-tension Re, below which the surface-temperature history is almost the same as the case of liquid droplets experiencing pure heat diffusion (Re 0), were determined. It was found that the effect of thermocapillary convection is more prominent for fluids with mid-Pr and for the conditions with finite-time-pulse duration. The results show that the critical Re is lower for mid-Pr fluids than for low-Pr fluids and thermocapillary convection is stronger for mid-Pr fluids. The finite-time-pulse duration also results in a lower critical Re. Transient streamline and temperature field contours are presented. The analysis of thermocapillary flow was also performed for positive surface-tension temperature coefficient fluids. It was shown that the resulting flow structure was totally different from that of negative surface-tension temperature coefficient fluids.