UNSTEADY 3-DIMENSIONAL MIXED CONVECTION IN A HEATED HORIZONTAL CHANNEL WITH APPLICATIONS TO CHEMICAL VAPOR-DEPOSITION

The flow and heat transfer of a gas in a horizontal channel with a heated bottom surface, a cooled top surface, and adiabatic side walls is studied. Numerical solutions of the transient, three-dimensional Navier-Stokes and energy equations reveal that the fluid is unstable thermally for conditions of interest in chemical vapor deposition (CVD). The instability appears as a combination of transverse, traveling waves and longitudinal rolls. The unsteady nature of the flow and the heat transfer is shown for two Reynolds numbers, Re = uHBAR/nu-0 (5 and 10), Grashof number, Gr = g-epsilon-H-3/nu-0(2) = 5000, Prandtl number, Pr = nu-0/alpha-0 = 2/3, aspect ratios, L/H = 8 and W/H = 2, for the temperature ratio epsilon = (T(s) - T0)/T0 = 0.01, corresponding to constant property flow. The instability results in an increase in the average heat transfer from 15% to more than 40% above the fully developed condition in the absence of the instability.