THERMOPHORETIC TRANSPORT IN THE OUTSIDE VAPOR-DEPOSITION PROCESS

A study has been made of the flow, heat transfer and thermophoretic deposition to a circular boule in respect to the outside vapor deposition (OVD) process. Numerical solutions of the governing conservation equations have been obtained utilizing a non-orthogonal curvilinear coordinate grid. The particle deposition rate and the variation of the deposition efficiency are investigated for a range of parameters relative to the OVD process. The interaction of the jet-like torch flow with the target and the surroundings results in a flow, heat transfer and particle transport to the circular target that are quite different from that for uniform flow. The increase in the concentration prior to the target is an important factor in determining the particle deposition rate. The effects of buoyancy augment the deposition rate. Larger values of the average Nusselt number and the efficiency are obtained for a cold target. For a hot target, the local Nusselt number becomes negative over the leeward side and a particle-free layer is formed. For the particle jet, the concentration and the deposition rate rapidly decrease downstream from the stagnation point. The deposition efficiency is greatly reduced when the torch is not aligned with respect to the target. Increasing the speed of the gas flow increases the average Nusselt number, but reduces the efficiency. Higher efficiency is obtained for a higher torch temperature. The efficiency is slightly increased for a larger target. Increasing the distance between the torch and the target and increasing the rotational speed of the boule slightly reduce the efficiency.