| Discharge in multi-phases is a usual natural phenomenon, now it may be a convenient way for the treatment of materials and pollutants. But it is a pity that systematic theoretical research on discharge in multi-phases can rarely be found all over the world so far. The article is focused on the discharge characteristics of air-solid mixture in non-uniform electric field, in which the influences on breakdown voltage and corona onset voltage of solid medium's permittivity and volume ratio, electrode gap, voltage type and polarity have been systemically researched. Numerical simulation on the process of discharge in multi-phase and the influence on the discharge process of solid medium is main part of the research. The result is as follows: In the parameters range used during the experiment, the positive breakdown voltage of air-solid mixture is higher than that of air, and in the case of negative, the converse is true. Polar phenomenon is observed in the course of breakdown experiment of air-solid mixture, and the higher the solid medium volume ration is, the earlier and more representative the phenomenon appears. In the condition of long electrode gap and high volume ratio of solid medium, the breakdown voltage of negative is always lower than that of positive. No matter what voltage type was used, breakdown voltage with large solid medium volume ratio is always lower than that with small volume ratio. The corona onset voltage of air-solid mixture is trending down as the electrode gap increase, and it vary from above the corona onset voltage of air to below it. This trend appears more obvious in the condition that higher solid medium volume ratio or positive DC voltage exists. Polar phenomenon of corona onset voltage is observed when DC voltage used, and it is different when we transform parameters such as volume ratio of solid medium. No matter what voltage type is used, corona onset voltage of air-solid mixture will always decrease as long as the solid medium's volume ratio or permittivity increases. For air-solid mixture, polar phenomenon of corona under AC voltage is in accord with that under DC voltage. Corona onset phenomenon always occurs in positive half of AC voltage when the volume ratio of solid medium is relatively high, vice versa. Numerical computation is conducted to simulate the discharge process of air-solid mixture, in which the influence on the stream development of electrical field and particle's distribution in space and time produced by solid medium is analyzed. The result is as follows: the electrical field of air-solid mixture is aberrant from that of air for the existence of solid medium. The dominating charge captured by the surface of solid medium is positive under positive DC voltage, and streamer is not move along the discharge symmetry axis near the solid medium, but move along the surface of solid medium. Meanwhile as the development of discharge, the surface region of solid medium where charges positive ions is extend. The variation tendency of net charge density of streamer head is different if the relative position of streamer head and solid medium is different. The developing velocity and process of streamer lie on both medium's characters and position. The numerical simulation developed in the work can well explain the difference of breakdown and corona onset voltage between the air-solid mixture and air. The research on the application of multi-phases discharge is included in the work. Pulsed corona discharge in gas-liquid mixture is used to remove SO2 from simulated flue gas and treat coke-oven wastewater simultaneously. The experimental result suggests the possibility of the application of multi-phases discharge in many fields, and may provide a new technology for desulfurization and coke-oven wastewater treatment in integrated steel plants. The work is helpful to understand the breakdown and corona onset characteristics of air-solid mixture, and is beneficial to cognize the insulation property and discharge process of multi-phases. It can also provide theoretical basis for the application of multi-phases discharge. |
