Electrostatic charging current characteristics for different fluid systems

Abstract

Electrostatic charging currents have been measured for the flow of several fluids (hydrocarbon solutions containing known concentrations of polar species) through small diameter stainless steel tubes. For tube diameters of 0·14 to 0·21 cm, solutions conductivities of 10 −16 to 10 −9 ohm −1 cm −1 and flow velocities of 200 to 1100 cm/sec, the charging current magnitudes for the fluid systems cover the range of 10 −13 to 10 −8 amperes. In general, the flow of non-polar solvents of low conductivity containing alcohols, acids, nitrobenzene, and ASA-3 produces positive tube currents. The flow of non-polar solvents of low conductivity containing ketones, esters, and amines produces negative tube currents. The charging currents show some dependence on the chemical nature of the polar additives. The currents obtained indicate that using the conductivity as the only independent variable for the charging phenomena is misleading. For low conductivity fluids, (δ EL ⩾ 1·3δ DL ), the measured charging currents increase as the conductivity increases. The experimental data of this region have been compared with current magnitudes predicted from Koszman and Gavis' modified form of Klinkenberg's diffusion equation. In this study, the experimental data show considerable scatter (approximately two-thirds of the data are within a factor of three of the predicted magnitude); but, the least squares line through all these data (approximately 3150 points) shows remarkably good agreement with the low-conductivity equation of Koszman and Gavis. A regression analysis gave a velocity and conductivity dependence which was slightly higher and lower respectively than the theoretically predicted dependencies. Charging current magnitudes exhibited no definite dependence on current polarity. For all fluid systems, measured/predicted current ratios show a relatively small variation with velocity changes and a greater variation with conductivity changes.