| 摘要: | 本研究致力於非熱電漿技術效能之改善，基於非熱電漿之化學反應乃由電子碰撞反應所生成活性物種所誘發之特性，本研究提出一套分析程序輔助非熱電漿效能改善工作之進行。該程序共包含三步驟，分別為釐清重要活性物種、瞭解該物種生成效率（單位能量輸入所產生之活性物種量）和折合電場(reduced field)之關係，最後依據上述分析結果將電漿系統之折合電場調整至較利於該活性物種生成之範圍。由於電漿物理和電漿化學反應相當複雜，僅藉由實驗進行上述分析極為不易。因此本研究亦發展一套非熱電漿數值模式，模式之模擬結果除和實驗數據趨勢一致外，兩者之數值亦相近，證實模式之可靠性。 為驗證上述分析程序是否可輔助非熱電漿效能改善工作，本研究選擇以O2/Ar混合氣體電漿生成臭氧及N2電漿去除NF3等議題進行案例探討。研究結果顯示Ar之添加並無助於臭氧生成，因其將導致折合電場之下降與氣體溫度之增加，兩者均不利於臭氧生成；而臭氧之主要生成途徑為O + O2 + M → O3 + M。另一方面，就NF3之去除而言，其於N2/NF3電漿中之主要破壞途徑為其與N2(A3Σ+u)（N2之一介穩態物種）之反應。由上述可知，O和N2(A3Σ+u)分別為此兩議題中最重要之活性物種，就效能改善之觀點而言，應提升上述兩活性物種之生成效率。 然值得注意的是O和N2(A3Σ+u)的生成效率隨折合電場之變化趨勢並不相同，O之生成效率首先隨折合電場上升而增加，但過高的折合電場反而不利於O之生成，亦即有一最佳折合電場存在；另一方面，N2(A3Σ+u)之生成效率單調地隨折合電場上升而增加。由於O的生成效率和折合電場之關係較為特殊，因此本研究選擇以臭氧生成議題進行效能改善之研究。 就介電質放電反應器而言，其折合電場視反應器之幾何條件而定。一般而言，縮短放電間距可提升折合電場。根據O的生成效率有一最佳折合電場之特性，可推論臭氧生成效能亦有一最佳放電間距。為驗證此推論之正確性，本研究利用三組不同放電間距之介電質放電反應器進行臭氧生成實驗，實驗結果顯示放電間距為0.2 cm之反應器，其所得臭氧生成效率優於間距為0.1 cm和0.3 cm者。因此本研究所提出的分析程序確實可供為非熱電漿技術效能改善工作之有效工具。 This study aims at enhancing the performance of nonthermal plasma for ozone generation and PFC removal. Based on the characteristic that the plasma chemistry is initiated by the active species generated by electron-impact reactions in nonthermal plasma, a three-step analysis procedure is proposed to assist the task of performance enhancement. This procedure consists of identification of important active species, understanding how the efficiency of the production of the important active species varies with the reduced field and optimzing the reduced field accordingly. Due to the complexity of plasma physics and plasma chemistry, it is difficult to carry out the analysis simply by experimental works. As a result, a numerical model is developed in this study as well. The model has been confirmed to be reliable because the simulation results show good agreement with the experimental data. To verify the validity of the proposed procedure, two topics, i.e. ozone generation in O2/Ar mixture and NF3 abatement in N2/NF3 mixture plasmas, are selected as case studies. The results indicate that adding Ar into O2 plasma is not a feasible approach to enhance the performance of ozone generation. The addition of Ar would lead to a lower reduced field and a higher gas temperature, which are both unfavorable for ozone generation. Moreover, the results show that the major pathway for ozone generation is O + O2 + M → O3 + M. As for NF3 decomposition, the results indicate that NF3 is mainly decomposed by N2(A3Σ+u), a metastable of N2. Therefore, the important active species for these two applications are O atom and N2(A3Σ+u), respectively. From the viewpoint of performance enhancement, one should improve the generation of these active species. However, it is worth noticing that the relationships between the O atom/N2(A3Σ+u) generated per eV and the reduced field are quite different. There exists an optimum reduced field in terms of O atom generation while the efficiency of N2(A3Σ+u) generation monotonously increases with increasing reduced field. The topic of ozone generation is chosen for further investigation because of the nonmonotonous characteristic of O atom generation. Since the reduced field of DBD reactor relies on its reactor geometry, it implies that the performance would vary as the reactor geometry changes. In general, reducing the discharge gap would result in a higher reduced field. Therefore, it can be expected that there exists an optimum discharge gap for ozone generation. Three DBD reactors with different discharge gaps are experimentally evaluated. The experimental and simulation results both show that the DBD reactor with a discharge gap of 0.2 cm could achieve better performance than those with gaps of 0.1 and 0.3 cm. Hence, it has been successfully verified that the three-step analysis procedure can be used to improve the performance of nonthermal plasma. |
