Application of DC voltages for determining flow electrification boundary conditions

In the nonaqueous weakly ionized hydrocarbon solutions where flow electrification has been a hazard, the charge transfer processes are not well understood because the ionic species are typically present in trace amounts and their chemical composition is unknown. As a result, postulated boundary conditions have been used, such as a constant zeta potential or wall charge density, a constant gradient in the volume charge density, or a wall current density that is proportional to the difference between the volume charge density and an equilibrium value. The applicability of these boundary conditions is explored. Measurements of the electrification volume charge density between rotating cylindrical stainless steel electrodes, with transformer oil filling the annulus between the cylinders, showed the steady-state charge density increasing linearly with low applied DC voltages (with fields of order 10³V/m). Transient measurements, with the inner cylinder covered by pressboard insulation, when the DC voltage is alternately connected and disconnected, suggest that the interfacial surface charge and electric field affect the electrification volume charge density