Current Pulsing: A Method to Reduce the Production of MagnetohydrodynamicElectrode Bubbles

摘要

Significant bubble production results during magnetohydrodynamic (MHD)applications in a conducting fluid. Bubbles, caused by the presence of an electrical field, create severe difficulties in collecting and analyzing reliable test data. Two of the most widely accepted flow measurement techniques, hot-film and laser Doppler velocimetry, have problems in sea water MHD flows. This report discusses some experiments conducted to understand the bubble production process more clearly and to quantify the formation of bubbles on MHD electrodes. Cyclical square-wave pulsing of the electrodes at differing frequencies and duty cycles was accomplished using a controller. Four different solutions of differing compositions and conductivity were examined to gauge this effect. To quantify the bubble-production processes, a closeup video camera that provided 150x magnification was used. A threshold voltage was then defined as the point at which gas bubbles were observed on the electrode surface. Threshold voltage was then examined as a function of time for the four conducting solutions examined. Finally, actual effects of bubble formation over operating hot-film probes were visually examined to demonstrate the effects of the bubble production on hot-film performance.