Analysis of Unsteady Heat and Mass Transfer During the Modified Chemical Vapor Deposition Process

An analysis of unsteady heat and mass transfer in the modified chemical vapor deposition has been carried out. It is found that the commonly used quasi-steady-state assumption could be used to predict the overall efficiency of particle deposition; however, the assumption would not be valid near the inlet region where tapered deposition occurs. The present unsteady calculations have been found to be capable of predicting the detailed deposition profile correctly even from the inlet region where further optimization is needed at a practical situation. The present results have also been compared with existing experimental data and were in good agreement. It is noted that previous quasi-steady calculation resulted in a significant difference in the deposition profile near the inlet region. The effects of time-varying torch speeds were also studied. The case of a linearly varying torch speed resulted in a much shorter tapered entry than the case of a constant torch speed.