Flow Effects in a Vertical CVD Reactor

A model is presented to simulate the non-Boussinesq flow in a vertical, two-dimensional, chemical vapor deposition (CVD) reactor under atmospheric pressure. Temperature-dependent conductivity, mass diffusivity, viscosity models, and reactive species mass transfer to the substrate are incorporated. In the limits of small Mach number and small aspect ratio, asymptotic expressions for the flow, temperature, and species fields are developed. The interaction of inertial and buoyancy-driven flows in a ramped temperature environment is described. The increase of heat at the reactor entrance leads to a recirculation of the flow at the entrance due to volumetric expansion of the gas. The recirculating flow forces the fresh incoming stream of gas toward the substrate. This, in turn, effects the species deposition rate. Soret diffusion effects are also investigated. Analytical solutions predict an inverse relationship between temperature field and concentration field due to Soret effects. This finding is consistent with numerical simulations, assisting in the understanding of the complex interactions amongst the flow, thermal, and species fields in a chemically reacting system.