水中超长脉冲放电的预击穿过程研究

Study on Pre-breakdown Process of Underwater Ultra-long Discharge

水中放电具有丰富的物化效应,在能源、环境、医疗等领域得到广泛的应用。预击穿过程对放电效应影响显著,很有必要厘清该过程中放电的发展机理。该文重点关注超长脉冲条件下(>100ms)水中针–板间隙的预击穿过程。研究表明,不同于脉冲条件下的流注发展主导模式以及直流条件下的气泡运动主导模式,超长脉冲条件下遵循气泡循环演化–流注猝发击穿的预击穿模式。当电压等级较低时,放电经初始液相扰动阶段后,针电极表面产生的大量气泡进入生长形变—脱离/破裂的循环演化过程。但在发散式液体对流的带动下,气泡群落难以形成贯通链路引发间隙击穿。当电压等级较高时,气泡不断扩张至临界尺寸后,内部电离放电并转变为(亚音速)流注,打破了循环演化过程,迅速使间隙击穿。进一步的分析表明,超长脉冲下气泡能否持续发展为流注并引发最终击穿,取决于使电极表面处气泡的生长膨胀(发展助力)与脱离破裂(发展阻力)间的动态平衡状态。

Underwater discharge has rich physical and chemical effects, which are widely used in the fields such as energy development, environment governance and clinical care. The pre-breakdown process has a significant influence on the discharge effect, so it is necessary to clarify the mechanism of pre-breakdown process. This paper focused on the pre-breakdown process of needle-plate gap under ultra-long pulse conditions. The research results indicate that: different from streamer development dominated mode under pulse condition and bubble motion dominated mode under DC condition, the ultra-long pulse condition follows the pre-breakdown mode of bubble cyclic evolution & streamer triggered breakdown. At low applied voltage, after initial liquid phase disturbance, the mass bubbles generated on needle electrode surface enter the cyclic evolution process of expansion & deformation to detachment/rupture. However, driven by divergent fluid convection, the bubbles is difficult to form a conductive bridge between the discharge gaps. At high-applied voltage, the ionizing discharge occurs after the bubble expands to critical size, and then the bubble evolves into(subsonic) streamer causing the final breakdown. Further analysis show that whether the bubble can develop into the streamer depends on the dynamic equilibrium state between the bubble growth & expansion(development assistance force) and the bubble detachment/rupture(development resistance force).