ON THE GASEOUS NATURE OF POSITIVE FILAMENTARY STREAMERS IN HYDROCARBON LIQUIDS .2. PROPAGATION, GROWTH AND COLLAPSE OF GASEOUS FILAMENTS IN PENTANE

This paper presents a study of the dynamics of positive streamer filaments in pentane using an optical method described in the text for pressures up to 9 MPa. It is observed that filaments expand and collapse, in a similar way to cavitation bubbles. Good agreement with the Rayleigh model shows that the dynamics of filaments is determined by liquid inertia. The influence of electric forces (electrostatic pressure) on the dynamics is found to be negligible. An evaluation of the energies involved shows that filaments are mainly composed of vapour, whose pressure varies with time and space and is on average higher than the hydrostatic pressure. Vaporization results mainly from energy dissipated at the filament extremity, which may be compared to a propagating point heat source of about 10 W power. At low pressure, a significant influence of energy dissipation within the filament, attributed to the transient current flowing during propagation, is also observed. At high pressure and/or high voltage, the stopping of the streamer is due to collapse of the gaseous filaments.