【作者】 王雪；

【导师】 温小琼；

【作者基本信息】 大连理工大学 ， 等离子体物理， 2023， 硕士

【摘要】 水下流光放电是研究水中放电基本物理、化学过程的主要研究对象。水下流光放电在高压开关、化学分析、食品加工、废水处理、癌症治疗等领域展现出良好的应用前景,近年来受到广泛的关注。水下流光放电产生数根流光丝,在低电导率(<100μS/cm)的水中,利用条纹相机已经发现了流光丝的再发光现象,即:流光丝的发光熄灭之后又再次发光,在条纹图像上表现为黑白交替的条纹。过去研究表明流光丝的再发光现象在电极间距大于10 mm时与外加电压变化等没有明显的关系,但是在较高电导率的水中观测不到流光丝的再发光现象。目前尚无法解释为什么在较高的水电导率条件下观测不到流光丝的再发光现象。本文利用四分幅超高速相机在20-800μS/cm水电导率条件下研究了水下微秒脉冲放电流光丝的再发光和暂停行为。探讨了为什么在较高的水电导率条件下难以观测到流光丝的再发光,本文主要研究结果如下:(1)通过对同一放电脉冲连续拍摄4幅发光图像,发现随着水电导率的增大,观测到流光丝的再发光现象的频度急剧减小,540μS/cm水电导率时降到零,再发光现象在不同的流光丝之间交替发生,并存在两种模式,一种为整根丝熄灭后再发光,一种为只有先端部分发光熄灭随后恢复发光。(2)通过观测流光放电的阴影图像,发现在20-800μS/cm水电导率条件下观测到冲击波串分段现象的频度在65%以上,表明在各种水电导率条件下流光丝在传播过程中都发生长时间暂停,流光丝的暂停时间平均为157±37 ns,水电导率几乎不影响流光丝的暂停时间。(3)通过分析流光丝轴向光强分布发现随着水电导率的增大流光丝的光强显著增大;在流光丝暂停期间(约157 ns),水电导率小于350μS/cm时,流光丝光强衰减到相机分辨能力以下,在发光图像上显示为熄灭状态;水电导率大于350μS/cm时,流光丝的光强无法衰减到相机分辨水平以下,在相机获得的发光图像上看上去是持续发光的,难以分辨出流光丝“熄灭-再发光”过程。更多还原

【Abstract】 The streamer discharge in water is a main object for studying the basic physical and chemical processes of an electric discharge in water.It has shown good prospects in the fields of high-voltage switching,chemical analysis,food processing,wastewater treatment,and cancer treatment in medicine,and has received widespread attention in recent years.Streamer discharge in water produces several streamers.The re-illumination phenomenon of streamer filaments has been found by streak camera in low-conductivity water(< 100 μS/cm),that is,the streamer filament quenches and then illuminates again,showing alternating stripes of black and white in the streak image.Previous works conformed that the re-illumination phenomenon of streamer filaments has no dependence on the applied voltage while the gap distance is larger than 10 mm,but cannot be observed at high water conductivity.It is not yet possible to explain why the re-illumination of the streamer filament is not observed at higher water conductivity.In this paper,the re-illumination and the pause behavior of a streamer filament of the microsecond pulsed streamer discharge in water of different conductivities(20 to 800 μS/cm)has been studied by an ultra-high-speed camera system.The cause for why the re-illumination of the streamer filament is difficult to be detected by the camera system as the water conductivity gets higher has been discussed.The main results are as follows:(1)By capturing four successive emission images during a single discharge pulse,we found that the appearance rate of the re-illumination of the streamer filament decreases rapidly as the water conductivity increases,and then drops to zero as the water conductivity goes beyond 540 μS/cm.The re-illumination alternately occurs among different streamer filaments,and two modes of the re-illumination are identified: one is that the whole filament quenches and then illuminates again;the other is that only the tip part of the filament quenches and then resumes illumination.(2)By observing the shadow images of streamer discharge,we found that within the water conductivity range of 20 - 800 μS/cm,the appearance rate of segmentation in shockwave pattern of the streamer filament is larger than 65%,indicating that the pause phenomenon is a common behavior of the streamer filament.The average pause period of the streamer filament is estimated to be 157 ± 37 ns,which is almost not affected by the water conductivity.(3)By analyzing the axial distribution of light intensity of the streamer filament,we found that as the water conductivity increases,the light intensity of the streamer filament increases rapidly.During the pause period of the streamer filament(about 157 ns),when the water conductivity is less than 350 μS/cm,the light intensity of the streamer filament decays to below the noise level of the camera system and is displayed as quench on the emission images.The light intensity of the streamer filament cannot decay to the noise level of the camera system during the pause period of the streamer filament as the water conductivity goes beyond 350 μS/cm.The streamer filament appears glow on the light emission image,which makes it difficult to distinguish the "quenching-illumination" process by the camera system.更多还原