CHARGE-DENSITY ENHANCEMENT DUE TO RECIRCULATORY FLOW

This paper develops a system model for electrification in a flow loop and investigates volume charge accumulation due to recirculatory flow between a charge source and several charge relaxation regions. Enhance d charge densities are predicted when the source is a filter and the r esidence time in the relaxation regions is small compared to the liqui d dielectric relaxation time. Small scale flow loop experiments verifi ed the enhanced charge densities. In these experiments, transformer oi l was circulated at volume flow rates of 0.063-1.26 l/s between a 208 l reservoir and a paper cellulose filter. The filter and the reservoir were electrically isolated from the rest of the flow loop and either grounded or virtually grounded through current measuring electrometers . The charge densities of the fluid entering and exiting the filter an d reservoir were measured using absolute charge sensors. Good agreemen t was obtained between the electrometer current and the calculated dif ference in convection currents. Bypassing the reservoir greatly reduce d the residence time for charge relaxation and resulted in increased v olume charge densities over the reservoir flow case. The charge densit y was found to have a strong dependence on temperature.