In this paper, the EHD coupled heat transfer systems have been investigated using a double electrodes' cylinder heat transfer model. Freon-11 is selected as working fluid. The condensation coefficient, the boiling heat flux and the saturation pressure are measured in this investigation. According to the experimental results, it is found that the electrical field can enhance both boiling and condensation heat transfer. The enhancement of condensation heat transfer is more obvious than that of only one electrode heat transfer model. The experimental results have been discussed.

This paper reports on the infuence of sintering conditions on the flashover/preflashover characteristics of alumina insulators in vacuum under an impulse voltage. Four kinds of alumina insulator were studied, which were prepared using the same formula with different sintering conditions. The surface pre-flashover and flashover phenomena of different samples in vacuum have been observed under impulse voltage. Based on the experimental results, the characteristics of pre-flashover and flashover vary with different kinds of test samples. It was found that the insulators with a higher sintering temperature had a lower flashover voltage, and more active pre-flashover. From a scanning electron microscope (SEM) analysis of alumina insulators, we conclude that the methods of preparing alumina samples can affect their microstructure resulting in a change in the pre-flashover and flashover performance as alumina insulators.

Investigations have been carried out on Alumina insulators in vacuum under an impulse voltage (0.7/4μS) in order to study the relationship between surface charging and surface preflashover phenomena of insulators in this paper. The Alumina insulators studied were 99.9% alumina cylindrical specimens and the employed electrode system is a non-uniform field electrode system. The surface preflashover phenomena were observed and the surface charge distribution of insulators was measured under varied impulse voltage levels and different shot number at a same fixed voltage level. Based on the experiments, it was found that the charge density and distribution is not only dependent upon the magnitude of the impulse voltage, but also the preflashover phenomena. The number of voltage shot has little influence on the charge density and distribution at the same voltage level if the surface preflashover phenomena can be observed during voltage shot.

This paper has investigated flashover performance of alumina insulators prepared with different additives in vacuum under an impulse voltage. Four kinds of alumina insulator were studied, which were prepared under the same sintering conditions with different additives. The surface flashover performance of these samples has been tested in vacuum. The microstructure of alumina samples has also been observed using the technique of scanning electron microscope (SEM). Based on the experimental results, the characteristics of flashover are different from the test samples. The analysis shows that the influence of additives may be attributed to the change of microstructure.

Recently surface flashover phenomena of insulators in vacuum were investigated with an impulse voltage (0.7/41as). The test samples studied were 99.9% alumina specimens. The impulse voltage, current and luminosity waveforms were observed whether a flashover occurred or not. Surface charges on insulator were also measured after impulse voltage application. Micro-discharge on the surface of insulators was observed in the experiments. The experimental results show that the micro-discharge occurs frequently as a kind of preflashover phenomenon and can be observed right before the current burst of flashover almost every time. It's considered that the micro-discharge is related to the accumulated charges on the surface, which initiates a flashover.