ASA 126th Meeting Denver 1993 October 4-8

2pPA11. An electrical-discharge, steam-bubble acoustic source---theory and experiment.

Allen H. Olson Stephen P. Sutton

Naval Command, Control and Ocean Surveillance Ctr., RDT&E Div., Code 711, 271 Catalina Blvd., San Diego, CA 92152-5000

Electrical energy stored in a high-voltage capacitor bank is rapidly discharged into seawater. Smooth spherical electrodes are used to achieve nearly uniform heating of the seawater in the inner-electrode gap. This allows the water to be superheated, in the liquid state, without electrical breakdown. As the high-pressure, high-temperature liquid expands against the surrounding hydrostatic load, the phase transition to steam occurs. The rapid volume growth of the steam bubble then gives rise to a very broadband, high-frequency acoustic pulse. Experimental data are presented for 1.9-cm-diam electrodes separated by 1.0 cm in 20 (Omega) cm seawater. The electrical resistance is shown to be a function of the energy delivered to the water. A fully three-dimensional conduction model is presented that takes the electrode geometry and known physical properties of seawater as input. The computation proceeds in constant energy steps, with spatial variation in temperature, electrical conductivity, and electric potential updated at the end of each step. The model accurately predicts the observed electrical resistance and the onset of steam formation.