Numerical modeling of diffusive physical vapor transport in cylindrical ampoules

Abstract Diffusion limited physical vapor transport in closed cylindrical ampoules of aspect ratio (length/radius) between 0.5 and 10 was studied numerically. The transport of a crystal forming component A through an inert component B, which undergoes zero net transport, was considered. A case in which the partial pressure of B is comparable to that of A, as well as systems with very low partial pressures of B (impurity cases) were treated. Concentrations and velocity distributions were obtained from the coupled transport equations for momentum, mass and components. It was found that the interdiffusion of components in viscous interaction with the container walls leads to (a) recirculation of component B, even in the absence of gravity; (b) concentration gradients normal to the main transport direction in the vapor space; and (c) non-uniform interfacial concentration gradients and, hence, non-uniform crystal growth rates.

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