The combined effects of thermocapillary and buoyancy Forces in an open cavity heated from one side have been modeled numerically. The configuration is that of two shallow, immiscible superposed liquid layers. High Prandtl number fluids are considered under both 1- and mu-g environments. The interfaces are considered deformable. It is shown that encapsulation strongly reduces the flow in the lower layer, and that a mu-g environment significantly reduces the flow in the lower layer. The sensitivity of the flow structure to some physical properties is also described, and particularly the relevance of the thermocapillary forces.