两相体放电实验和仿真研究及其在环保中的应用初探

【作者】 邵瑰玮；

【导师】 李劲；

【作者基本信息】 华中科技大学 ， 高电压与绝缘技术， 2005， 博士

【摘要】 多相体放电的现象既存在于某些自然现象中,又是等离子体用于材料处理和环境污染物处理时一种极方便的形式。但长期以来,国内外关于混合两相体/多相体放电现象的系统研究未见报道。本文以空气—固体混合两相体为研究对象,系统地研究了固相物占空比、介电常数、放电间隙、外加电压极性和种类对气固两相体击穿和起晕电压的影响; 采用自编程序对颗粒物对放电发展过程的影响进行了理论计算。研究成果包括如下几点: 实验范围内,气固混合两相体的正极性击穿电压大于空气的击穿电压,负极性击穿电压则相反; 其击穿存在极性效应,在长放电间隙、高占空比时,负极性的击穿电压低于正极性的。随着占空比增大,该极性效应越明显,出现得越早; 实验范围内,不论是直流还是交流电压,占空比大的气固混合两相体击穿电压值总是低于占空比小的。固相物介电常数大的击穿电压低。交流下,气固混合两相体的击穿电压大于单纯空气的击穿电压。根据占空比不同和放电间隙不同,击穿在交流电压的正、负半波都可以发生。随着放电间隙的增大,气固混合两相体的起晕电压有从高于单纯空气间隙的起晕电压向低于单纯空气间隙的起晕电压转变的趋势,占空比越大其趋势越明显,正极性比负极性明显; 直流电压下,气固混合两相体的起晕电压存在极性效应,不同的占空比下存在不同的极性效应; 不论是直流还是交流电压下,占空比大的气固混合两相体的起晕电压低,固相物介电常数大的起晕电压低。交流电压下,占空比高的两相体在正半波起晕,低的则相反,其规律与两相体直流起晕的极性效应相吻合。对气固混合两相体中颗粒介质对放电发展过程的影响进行了数值计算,分析了颗粒物的存在对放电中各种粒子密度的空间分布和变化对流注发展过程的影响,计算了气固混合两相体放电过程中电场强度的分布及变化规律,得到如下结果:颗粒介质对电场存在畸变作用,在正极性电压下,颗粒表面荷正电荷; 随着放电时间的推移,颗粒表面荷正电荷的区域逐渐扩大; 在颗粒表面附近,流注运动方向不再是沿着放电对称轴,而是紧贴着颗粒表面移动; 随着流注与颗粒介质的相对位置不同,流注头部净电荷密度呈现不同的变化趋势; 流注的发展速度和发展进程由颗粒介质的物性和其空间位置共同决定; 数值计算结果能较好地解释气固混合两相体击穿、起晕电压与单纯更多还原

【Abstract】 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.更多还原