Transient thermocapillary flow in rectangular tanks with phase change

A numerical and experimental study is performed on transient natural convection in an insulated rectangular tank. The liquid is suddenly heated by a line source or cooled by a line sink being placed at the center of the free surface to initiate a thermocapillary force. Evaporation or condensation takes place on the free surface. A finite-difference technique is employed to numerically integrate the unsteady vorticity and heat transport equations. Numerical results are obtained to determine the effects of dimensionless governing parameters on the transfer phenomena. In an evaporative system with low Marangoni number (Ma), three distinct convective mechanisms are identified: surface. tension-driven, buoyancy-driven and mixed types. The differences in the flow behavior are disclosed between condensation, evaporation and no phase change. Theory is in qualitative agreement with evaporation experiments in high Ma systems.