Study On The Properties Of Water–Air MHCD Jet And The Application For Sterization

·OH, an environmental-friendly radical with the strongest oxidation except for fluorine, is the most effective reactive oxygen species（ROS） to organisms. To improve ·OH production, a water-air micro-hollow cathode discharge（MHCD） plasma jet device was designed and fabricated. MHCD jet device can use air as work gas, which is low cost and is helpful to generate O. Besides, MHCD jet device has obvious advantages, such as simple structure, low cost, high ionization rate, low jet temperature, which make it especially suitable for biological applications such as sterilization. Influences of applied voltage, water content and mode transformation on jet characteristics including jet of length, temperature and products were fully investigated. This device was also used in inactivation experiment of P. digitatum suspension.Firstly, in order to study the influences on jet properties after water vapor mixed in the working gas, the change rules of jet length, temperature and discharge modes effected by parameters such as applied voltage, water content and gas flow rate were studied in this paper. Two discharge modes of water-air MHCD jet have been found. With the increasing of voltage, discharge mode changed from self-pulsing discharge mode to DC mode, and the critical voltage value of discharge mode increased with the rise of gas flow, which was not directly related to water content. Meanwhile, the increasing water content resulted in jet length shortening and temperature increase. When the flow rate was 150 L/h, jet length was 4.5mm to 11 mm, and the temperature ranged from 24.7 ℃ to 39.4 ℃ at 4mm to the nozzle.Secondly, in order to study the influences on the products content of water-air MHCD jet, an emission spectrum diagnosis system was established to measure the relative content of ·OH and O. It was found that water content, applied voltage and discharge pattern affected the relative content of these products. ·OH can be detected only in DC mode and O in both self-pulsing and DC discharge modes. In addition, water vapor in working gas promoted the generation of ·OH, but inhibited the generation of O.At last, in order to study whether water-air MHCD jet was useful when didn’t contact with the fungus directly, inactivation experiment of P. digitatum suspension was conducted. Although jet had no direct contant with suspension, it turned out that water-air MHCD jet improved the inactivation efficiency. Meanwhile, the more water vapor in the working gas, the higher inactivation efficiency was. In the condition of indirect contact with P. digitatum suspension, free radicals such as ·OH were difficult to transfer into suspension, so the concentration of H₂O₂ was detected, which was long-life. It’s found that water-air MHCD jet was helpful to generate H₂O₂ in the solution, which may be one of the reasons to improve the inactivation efficiency. Besides, the pH value of P. digitatum suspension decreased obviously, which may also be a possible cause of P. digitatum inactivation.In conclusion, the properties of water-air MHCD jet and the inactivation efficiency without direct contact were studied in this paper. The results showed that water-air plasma jet was useful to improve ·OH concentration and inactivation efficiency, which were able to provide bases in the related applications.