Shinjiro Umezu

Electrohydrodynamic deformation of water surface in a metal pin to water plate corona discharge system

Electrohydrodynamic deformation of water surface was investigated in a pin-to-plate gas discharge system that consisted of a pin electrode made of metal and an ion-conductive water electrode. In the condition of a lower applied voltage than the corona threshold, because an extremely small electrostatic attractive force, a Coulomb force in the order of 10 µN, was induced, water lifted up in the order of several tens of micrometres at the centre. Over the threshold voltage corona discharge took place and a relatively large repulsive force, in the order of 100 µN, was induced due to the ionic wind. It depressed water in the order of several hundred micrometres at the centre. Deformation of the water level coincided with the pressure distribution on the metal plate electrode, if the surface tension of water and the Coulomb force was included in the estimation to derive the pressure distribution from the measured deformation of the water level. If the applied voltage was lower than the corona threshold, total force to the water electrode coincided with that to the pin electrode. However, it was larger than that to the pin electrode at the corona discharge because the reaction force due to the ionic wind was applied not only to the pin electrode but also to other parts of the electrode at the corona discharge.

Force at Spark Discharge in Pin-to-Plate Gas Discharge System

It was investigated whether the electrostatic force was generated at the spark discharge on a pin electrode in a pin-to-plate gas discharge system. Because it was not possible to measure the force directly at a short sparking period, three independent metcods were employed to evaluate the existence of the force indirectly. (1) Axial vibration was observed at the intermittent spark discharge for the softly supported pin electrode. The force was explicitly calculated in the case that the calculated vibration was well agreed with the measured. This experiment indicated that the force was almost 0 N at the spark discharge. The vibration was generated not by the force at the spark discharge but by alternative ionic wind at corona discharge. (2) A similar experiment was conducted whether the vibration magnitude depended on the spark current. The current at the spark discharge was varied by a circuit resistor. The experiment deduced that the force did not generated at the spark period and it was independent on the current. (3) Axial vibration could be observed when the voltage pattern that was common with that with the spark discharge was applied, if no force was applied to the pin electrode. To confirm it an experiment was conducted with two parallel-connected pin-to-plate gas discharge systems, one of which air gap was shorter than the other. The axial vibration of the longer air gap, in which the spark discharge did not take place, was observed and vibration also agreed quantitatively with calculated one. These three results suggested that no substantial force was generated at the spark discharge.