1. School of Electrical Engineering Zhengzhou University Zhengzhou 450052 China; 2. Beijing International S&T Cooperation Base for Plasma Science and Energy Conversion Institute of Electrical Engineering Chinese Academy of Sciences Beijing 100190 China; 3. University of Chinese Academy of Sciences Beijing 100049 China
Abstract：Plasma-activated water produced by gas-liquid plasma discharge is rich in reactive oxygen species and reactive nitrogen, and it has a wide application prospect in the fields of environmental treatment, material synthesis, and medical health. However, how quickly preparing large volumes and high concentrations of activated water of RNOS is still a difficult problem, and the design of a gas-liquid plasma reactor is one of the key factors to solve this problem. In order to solve these problems, this paper designed a "multi-microporous coaxial" microbubble plasma reactor, which uses multi-microporous microbubbles to reduce the breakdown field strength of the liquid phase, and forms multi-spark discharge channels in the liquid phase, so that rich active oxygen and nitrogen can be generated in the liquid phase. Under the excitation of nanosecond pulses, the factors influencing the nitrogen fixation of microbubbles by coupling nanosecond pulse liquid discharge in a microbubble plasma reactor were investigated. Firstly, this paper explored the influence of positive and negative pulse parameters on the nitrogen fixation characteristics of activated water. The results showed that the output of NO−2 and NO−3 under positive discharge was 7.2 mg and 28.8 mg respectively. Because of the voltage polarity effect and the different development of positive and negative currents, the output of NO−2 and NO−3 were 0.43 mg and 3 mg higher than that of negative discharge, respectively. The energy efficiency of positive discharge was calculated to be 15.02 g/(kW·h). At the same time, it was found that the airflow rate affected the nitrogen fixation efficiency, and the best flow rate for nitrogen fixation performance was 2 L/min. In addition, nitrogen fixation efficiency is also affected by water temperature. In this paper, the lower the water temperature is, the higher the nitrogen fixation efficiency is. Because the solubility of oxygen and other gases will decrease with the increase in temperature, affecting the process of N2 and O2 discharging to generate NOx. Secondly, this paper measured the plasma emission spectrum during discharge, analyzed the physical and chemical reactions at the gas-liquid interface according to spectral characteristics, and deduced the reaction path of nitrogen and oxygen. The physical and chemical characteristics of activated water during the discharge were investigated. It was known that the generation of active substances in the gas and liquid phases was also an accumulation process. The liquid phase spark discharge produced a large number of active particles to dissolve the water, resulting in a decrease in the pH of the solution, an increase in ORP, and an increase in conductivity. The water temperature rises about 5℃ due to the "hydroelectric effect". Finally, the analysis of electrical characteristics showed that microbubbles and micropores distort the electric field in the liquid phase, making the liquid phase discharge more likely to occur. The following conclusions can be drawn from the analysis: (1) The microbubble coupled plasma discharge device is designed, which can continuously generate microbubbles and reduce the breakdown field strength; and it can also reduce the loss of metal electrodes and discharge in the liquid with high conductivity, forming a multi-electrode spark discharge channel. (2) The nitrogen fixation efficiency of positive discharge is higher than that of negative discharge. The main reason is that the voltage polarity effect is different from the development of positive and negative currents. (3) The nitrogen fixation efficiency of the activated water increases with time, but it is lost in the form of heat energy due to the polarity effect during discharge. Setting a lower water temperature can reduce the energy loss due to heat during discharge, and the number of active particles generated is higher. This paper provides a new way for the nitrogen fixation model.
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2023, Vol. 38 
