| dc.description.abstract | 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.
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