Experimental investigation of the behavior of microscopic bubbles in insulating liquids: influence of pressure and temperature

The dynamics of microscopic bubbles in insulating liquids is investigated by optical methods. Each bubble is created by a fast and localized injection of electrical energy (∼nJ) initiated by a very high divergent electric field. Current pulse, bubble dynamics and emitted pressure waves are simultaneously measured as a function of hydrostatic pressure P_∞ (in the range 0.1-10 MPa), temperature (in the range 20-100°C) and nature of hydrocarbon liquids. Then, the distribution of energy is calculated and compared to available theories. The main results are: i) a bubble is formed whatever the temperature and the applied pressure, including those above the critical pressure P_c of the fluid, and ii) for P∞ > P_c, the maximum bubble size can be calculated from an evaluation of an equivalent "latent heat" (a latent heat has no meaning above P_c). In this case, the thermodynamic model uses an extrapolation of the saturated vapor pressure curve to define the conditions of "phase change" (i.e. a phase of smaller density than the liquid one).