Effect of thermodynamic parameters on AC breakdown initiated by thermal induced bubble of inflammable fluorocarbon

摘要

Preliminary research of AC breakdown voltage of thermal bubble induced two-phase flow condition of inflammable fluorocarbon by self-heating plane-plane electrode has been reported before. Further breakdown experiments by sphere-plane electrodes with different gap distance and working pressure have been accomplished in this paper. According to the experimental outcomes, the AC breakdown voltage of sphere-plane electrodes reproduced the “Z” shaped variation curve of plane-plane electrodes, which could be divided into three sections according to the surface heat density: In first section it nearly equals to the value of normal liquid with no heat density; and in the second section it drops sharply until it reaches the value of vapor. Along with the drop of breakdown voltage, the flow pattern and the superheat degree ΔT on the surface of self-heating electrode also changes with the heat density q. The test results illustrate that ΔT increases with q as power function until q reaches a threshold, where the visible bubbles appear firstly, and at the same time both of ΔT and breakdown voltage drops sharply. The change and influence of thermodynamic parameters like flow pattern and surface superheat have been discussed. The eigenvalues and eigenvectors to represent the converting point of BDV have been found to be applied in practice.