Ap. Washabaugh et M. Zahn, CHARGE-DENSITY ENHANCEMENT DUE TO RECIRCULATORY FLOW, IEEE transactions on dielectrics and electrical insulation, 1(1), 1994, pp. 38-52
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.