Transient electric charging of dielectric liquids in recirculation systems

This paper describes a transient electric charging phenomenon due to flow-induced electrification during a cold startup of dielectric liquids in a recirculation system. This transitory effect exhibits itself as a static voltage spike in the system. It is argued that simultaneous rise in the liquid temperature and the circulation flow rate can generate conditions for such electrostatic voltage spikes to exist. These spikes have been verified experimentally in the laboratory and we report qualitative agreements between the reported experimental data and the theoretical considerations. With a cold start, this transient charging has the potential to induce a large static voltage and large space charge in the circulating system that can damage other components. •We discuss electrostatic hazards associated with a cold start of a power unit.•The paper utilizes the proper variation of electrical conductivity of a dielectric liquid with temperature.•The paper proposes a new electric charge boundary-condition at a solid--liquid interface.•We derive theoretical expressions that explains physical conditions under which a voltage spike can take place in a circulating system.•A charge density probe is utilized to record voltage spike of a power unit.