Pressure generation from micro-bubble collapse at shock wave loading

To explore a reliable technology possibly applicable to the inactivation of micro-creatures in ship ballast water, this paper reports a result of a primary experimental and analytical study. We obtained 10 μm bubbles in averaged diameter by using a swirling flow type micro-bubble generator. We exposed a shock wave generated by a micro-explosion of a 10 mg silver azide pellet to the water containing micro-bubbles filled in a 10 mm wide parallel test section. Observations were carried out with a high-speed camera, and the corresponding rebound pressures of bubbles were measured with a fiber optic probe pressure transducer. We confirmed micro-bubble motion with higher temporal resolution and found that micro-bubble collapse arose in several hundred nano-seconds after the shock loading. The peak pressure generated by bubble collapse was over 200 MPa at the distance of 20 mm from the explosion center. These experimental results were consistent with those analyzed on the basis of the measured pressure data. The presence of such high impulsive pressures upon bubble collapse clearly indicated that the rebound pressure would be effectively applicable to the inactivation of microcreatures in ship ballast water.