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

This paper presents a study of the dynamics of positive streamer filam ents in pentane using an optical method described in the text for pres sures up to 9 MPa. It is observed that filaments expand and collapse, in a similar way to cavitation bubbles. Good agreement with the Raylei gh 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 pre ssure varies with time and space and is on average higher than the hyd rostatic pressure. Vaporization results mainly from energy dissipated at the filament extremity, which may be compared to a propagating poin t heat source of about 10 W power. At low pressure, a significant infl uence of energy dissipation within the filament, attributed to the tra nsient current flowing during propagation, is also observed. At high p ressure and/or high voltage, the stopping of the streamer is due to co llapse of the gaseous filaments.