THERMOCAPILLARY CONVECTION IN 2-LAYER SYSTEMS

This paper concerns a numerical study of the flow characteristics of t hermocapillary convection in a system composed of two immiscible liqui d layers subject to a temperature gradient along their interface. We c onsider the two-layer system: B2O3 (encapsulant) and GaAs (melt), for its experimental relevance in crystal growth by the directional solidi fication method; Two cases have been studied: a system with only one l iquid interface (melt/encapsulant) and a system where the outer surfac e of encapsulant is open to air (and so, subject to a second thermocap illary force). Both the liquid-liquid interface and the outer surface are assumed to be undeformable and flat, which is a valid assumption a ccording to earlier theoretical and experimental results. A 2-D numeri cal simulation of convection is carried out in a rectangular cavity by solving the system of Navier-Stokes equations using a finite differen ce method with a staggered grid for the pressure. Having in perspectiv e a Spacelab experimentation we disregarded gravity (g = 0). We show t hat a strong damping of the melt flow can be obtained by using an enca psulant liquid layer having appropriate viscosity, heat conductivity a nd/or thickness. (C) 1998 Elsevier Science Ltd. All rights reserved.