DYNAMIC SIMULATION OF THE VERTICAL ZONE-MELTING CRYSTAL-GROWTH

Dynamic behavior of heat transfer, fluid flow, and interfaces in the v ertical zone-melting (VZM) crystal growth is studied numerically. The model, which is governed by axisymmetric unsteady-state momentum and h eat transfer and interface balance in the system, is solved by a robus t finite-volume method. Single crystal growth of NaNO3 in a computer-c ontrolled transparent multizone furnace is simulated as examples. The effects of gravity levels and heater temperature are considered. Multi ple steady states obtained at stationary cases are used as initial con ditions to illustrate the transient response and the stability of the VZM crystal growth to the pulse and step changes in thermal environmen ts. For unstable cases, periodically oscillatory flow and growth rate occurring at intermediate values of the Rayleigh number are observed. The upper flow cells beneath the feed front seems to be responsible to the instability, and this is consistent with the observation during c rystal growth experiments. For stable cases, a steady state can be ach ieved smoothly, and the calculated results are in good agreement with the ones from a pseudo steady-state model. (C) 1998 Elsevier Science L td. All rights reserved.