NEW WAYS FOR INFLUENCING THERMOPHORETIC EFFICIENCY IN THE MCVD PROCESS

The thermophoretic efficiency in the modified chemical vapour depositi on process has been experimentally studied under conditions of changin g temperature and velocity field in the silica deposition tube. The co oling of the tube by a stream of air, deposition under the reverse tor ch traverse and induction of a circular flow in the tube have been stu died. Results of the experiments were explained on the basis of the Wa lker thermophoretic model and under the assumption that the amount of the deposited glass is determined by chemical equilibrium. Considerabl e increase of the overall thermophoretic efficiency was observed when cooling by the air stream was used. The derived theoretical model can account for these results.