COMBINED THERMOCAPILLARY AND BUOYANCY-DRIVEN CONVECTION WITHIN SHORT-DURATION PULSE-HEATED LIQUID DROPLETS

Abstract

Buoyancy-driven convection and its interaction with thermocapillary flow within shortduration-heated liquid droplets was studied computationally. A parametric study was conducted to investigate the effect of the Grashof number Gr and the surface-tension Reynolds number Re for fluids with different Prandtl numbers Pr having both negative and positive surface-tension temperature coefficients. Both the additive and impeding effects of buoyancy-driven convection on the thermocapillary flow were observed. The numerical analysis indicated that the buoyancy-driven convection has a weak effect on low-Pr fluids during the short-pulse-heating condition. For mid-Pr fluids the buoyancy effect is more prominent. In monitoring the history of the surface temperature rise, it was found that the buoyancy-driven convection has a weak effect for low-Pr fluids at the side and bottom observation points, whereas buoyancy-driven convection has substantial influence at the bottom observation point for mid-Pr fluids with a positive surface-tension temperature coefficient. It was concluded that the presence of additive or impeding modes depends not only on the sign of the surface-tension temperature coefficient of fluids as proposed by other researchers, but also on Pr, geometry, and boundary conditions. The finite-time-pulse duration effect was also simulated, and it was concluded that the finite-time pulse enhances both modes of convection.