水溶液中電漿性質檢測：藉不同驅動電源型式操控電漿行為之策略

Diagnostic Study of Electrical Discharges in Saline Solution: Strategies to Tailor Plasma Behavior via Different Power Types

張鴻文(Hung-Wen Chang)

指導教授 ： 徐振哲

國立臺灣大學/工學院/化學工程學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.01347

摘要

水溶液中的電漿提供了在液相中生成高反應性物質的可能性。而這種在水溶液中氣泡內所生成的電漿放電性質和此氣泡有密切的關係，然而對於主動調控氣泡表現或組成的方法仍相對缺乏。此研究中，我們將提出藉不同驅動電源型式來調控氣泡藉此改變電漿行為的策略。
不同於先前文獻之研究利用直流電源來驅動電漿，本研究選用具有週期表現的交流電源。藉由調控驅動電漿的電壓和頻率，可觀察到兩種不同的氣泡表現：在同為電壓150伏特下，當利用相對低頻率(如 50赫茲)驅動電漿，電漿會生成在一個數釐米的氣泡中；利用相對高頻(如500赫茲)時，可觀察到氣泡的噴流。依氣泡的表現而定，我們將這兩種不同的氣泡表現稱為氣泡模式及噴流模式。本研究發現，當利用交流電源驅動電漿時，頻率可控制電極附近之加熱行為，進而影響氣泡和電漿的表現，電漿特性如系統的電流和電子密度都和頻率有密切的關係。然而使用交流電源時，兩種不同極性(正及負電壓)被交錯用以驅動電漿，因而造成了電極損壞，電漿不穩定性及生成電漿效率不佳三個主要問題。全波整流後的交流電源將被用以改善此問題。在低頻的氣泡模式及高頻噴流模式，施加相同電壓下，整流後正極性電源驅動電漿的電流均約僅為負極性驅動電漿電流的十分之一。正極性驅動電漿所損耗的功率最低可小於負極性驅動電漿一個尺度。此結果顯示，整流後正極性交流電源是一個較理想驅動電漿方式。最後，為達控制氣體組成之目的，可獨立控制正負脈衝長度及大小的雙極性脈衝電壓被用來獨立控制氣泡生成和電漿的驅動。電壓為0到負80伏特的負脈衝被用來生成電解氣體，在驅動電漿前覆蓋在電極上，而600伏特的正脈衝電壓則用以驅動電漿的生成。藉此方法，可觀察到在施加正電壓時電漿生成時間的延長，系統最大電流值的減少，及光譜中相對氫發射光譜強度的提升。研究結果證明藉改變驅動電漿電源之型式，調控正負脈衝的大小及長度，氣泡的生成及電漿表現可有效的進行調控。

關鍵字

水溶液中放電現象 ； 電漿 ； 電源型式 ； 氣泡表現 ； 頻率響應 ； 極性響應 ； 氣體組成

並列摘要

Discharges in solution provide the possibility to generate reactive species in liquid phase in demand. The discharge behavior has been proved highly relevant with the behavior of bubble where the plasma is ignited, however the methods to actively manipulate the bubble dynamics and composition are still limited. In this study, strategies to tailor the plasma behavior via different power types are proposed.
Unlike previous study in which plasma was driven by a direct-current power, a time-varying voltage was used to ignite the plasma. Two distinct bubble modes can be observed by adjusting the applied voltage and frequency: at 150 V, when a relatively low frequency (e.g. 50 Hz ) is used, the plasma is sustained inside a gas bubble with diameter of few mm; when a relatively high frequency (e.g. 500 Hz) is used, a jetting flow is observed. Depending on the bubble dynamics, we therefore called them as bubble and jetting mode, respectively. According to our study, it is known that frequency serves as an effective factor to control the heating in the vicinity of electrode surface, thus influencing the bubble and plasma behavior. The current and electron density in plasma are changed in response to the frequency. However, when plasmas are driven by an AC power source, plasmas are ignited by positive and negative polarity alternatively, and thus three issues are raised, namely damage of electrode, plasma instability, and poor power efficiency. A rectified AC power source was used in order to further improve the system. For both bubble mode and jetting mode, the discharge current for positively rectified AC- (PRA) driven plasma is only one tenth of that for negatively rectified AC- (NRA) driven plasma. The power consumption for PRA-driven plasmas is at least one order lower than that for NRA-driven plasmas. The result shows PRA-power is ideal to sustain the plasma. Finally, in order to control the gas composition, a bipolar pulse power source with adjustable positive and negative pulse width and amplitude was used to independently control the gas bubble formation and plasma ignition. Negative pulse with voltage from 0 to–80 V is used to generate the electrolytic gas bubble where plasma is formed and 600 V positive pulse is used to ignite the plasma. By this approach, the extension of plasma occurrence time in the positive pulse duration, the drop of peak electrolytic current, and the increase in relative H emission intensity are observed. These results suggest that by manipulating the driven power types, the gas composition and the discharge behavior can be effectively tailored.

並列關鍵字

discharges in solution ； plasmas ； power types ； bubble dynamics ； frequency effects ； polarity effects ； gas composition

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