| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 102 === In this study, numerical simulation of the nitrogen plasma jet at atmospheric pressure is performed. In terms of commercial software, three types of models, namely k-ε turbulent flow model, heat transfer in fluids model and chemical reaction model are adopted.
Without complication of plasma reactions in the first place, we couple the k-ε turbulent flow model and heat transfer in fluids model to simulate the flow of PECVD chamber. Simulation results show that the modified design of chamber weakens the vortex and makes the mixed material delivered straight and uniformly, hence improve the quality of coating. Furthermore, in order to build a reliable chemical model for plasma simulation, we implement an atmospheric pressure plasma jet model. We compare the simulation results with the experiment results to validate the chemical model. Simulation results show that visible jet length and width will grow in a sudden when the height of plasma jet is lower than a certain height, which conforms to the observation of experiment results. This is due to the streamlines show that there is a backflow carrying the oxygen into the tube, and the excited state nitrogen densities decrease drastically due to the interaction of oxygen and the jet, which leading to quench. Based on the chemical model, we analyze different geometry design in the PECVD downstream. Simulation results show the profiles of oxygen density in the downstream of modified design of chamber are fewer, which means that excited state nitrogen has been quenched less, hence the light emission intensities are greater. With the effects of a porous plate, the flow appears much more uniform, with stronger reactions of plasma.
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