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論文題目「Investigation of Discharge Characteristics of DC Arc Water Plasma」

Feng Tainlun

In the master’s thesis, the discharge characteristics of DC arc water plasma generator, which was developed to decompose liquid or gas waste, were examined with the change in working parameters. The DC arc water plasma generator used in this study needs no additional cooling system, and the plasma supporting gas is directly fed by the evaporation of cooling water.

DC thermal plasma processing is widely applied in various fields, such as nanomaterial synthesis, plasma cutting and spraying, and environmental science and technology. Many fundamental studies are being performed to improve the controllability of reaction processes, to develop a sophisticated plasma processing system, and to minimize the energy consumption. Reports show that discharge characteristics such as the fluctuation of plasma arc and jet, seem to affect the controllability and reliability of plasma heating processing. However, these studies are mainly performed in traditional DC arc generation.　The purpose of this study is to investigate the discharge characteristics of DC arc water plasma and optimize the discharge condition for water plasma generator.

The discharge characteristics of DC arc water plasma were examined by using oscilloscope, high speed camera, and optical spectrometer. And accordingly, the stabilities of plasma in different experimental conditions were determined. The electrode performances in DC arc water plasma were examined by studying the erosion of electrodes by camera, microscope, and XRD, as well as measuring the erosion rate of copper on electrodes by ICPS.

The discharge stability of DC arc water plasma affected by both physical and chemical factors was discussed for the improvement in the application of DC arc water plasma generator.

For physical factors, the periodical variation of arc voltage of about several tens of kilohertz was found to be caused by the axial movement of arc attachment on anode and the frequency. And the mean arc voltage and frequency was strongly influenced by the feed rate of plasma gas. Larger gas feed rate cause larger mean voltage and frequency.

For chemical factors, plasma discharge was found to be favored by the carbon existing in the plasma gas instead of pure water, and which could lower the arc movement speed. In addition, carbon existing in both plasma gas and cathode material can actually reduce the oxidation of metal used as the cathode material.

Considering the stability of plasma arc and jet for this plasma generator running at a long time, Hf material, 1mm diameter, 8 A current, 1mol% ethanol solution as plasma gas, and 2-3 mm distance between electrode could be the best condition for plasma discharge used in plasma cutting process.　However, to improve the DC arc plasma generator used for the decomposition of various organic wastes, a controllable gas feeding system might be necessary when using different organic wastes as plasma supporting gas in order to assure the most stable plasma condition.


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