Control of Natural Circulation Loops by Electrohydrodynamic Pumping

The paper analyses the effect of electrohydrodynamic (EHD) pumping on the stabilization and control of natural circulation loops (NCLs). In the initial experimental set-up, we measured the static pressure rise given by an EHD pump made of three consecutive modules of point-ring electrodes for different dielectrics fluids and electrode materials. When switching the polarity of the applied voltage, we observed opposite pumping directions, suggesting the presence of two distinct EHD phenomena, inducing motion on opposite directions: ion-drag pumping and conduction pumping. Based on these preliminary experiments, we built an NCL, operating with the fluid HFE-7100. Two oppositely mounted pumping sections could be alternately activated, to promote clockwise or anticlockwise motion. In the first series of tests, alternately, the pumping sections were triggered prior to the heat input. In any case, the circulation followed the EHD pumping direction. In other tests, the electric field was applied when natural circulation was already present and the flow was reversed by means of opposite EHD pumping, at both polarities. Simply inverting the polarity of the applied voltage, we could alternate ion-drag and conduction pumping; in this way, we easily controlled the direction of motion by means of a single pumping section.