| Based on the experimental finding of certain convection patterns inside evaporating sessile drops, and also because of the increasing interest in surface-tension driven flows, a finite difference code is developed using an ADI scheme to study the thermocapillary-buoyancy convection induced by phase change in a drop-shaped system.; The intercoupling relation between thermocapillary force, buoyancy force, heat transfer, and phase change, along with their effects on the induced flow patterns, is disclosed. Three types of convection can be classified based on MaRa: thermocapillary-dominant, competing, and buoyancy-dominant. Among these three types, the competing type of convection simulates the experimental observations quite well, the basic mechanism of the observed convection inside evaporating sessile drops is thus understood.; A critical Ma number of 10('4) is found for transition from linear flow behavior to nonlinear in the thermocapillary-dominant case. For the more familiar buoyancy-dominant convection, onset of flow separation is found at Ra = 10('6) with Pr = 17.6.; Both evaporation and condensation are examined; only evaporation initiates the unstable convection, while condensation always brings out a stable density distribution that eventually damps out all the fluid agitation. A simple numerical model is also presented to study the effect of boundary recession due to evaporation and the peeling-off effect (the removal of the surface layer of fluid by evaporation) is shown to be relevant. |
