Study of Sterilization Effects on Marine Vibrio sp. using Interaction of Cavitation with Shock Wave in a Narrow Water Chamber

Abstract

When underwater shock waves are generated by an electric discharge in a narrow water chamber, the instant release of a great amount of energy causes the propagation of a shear wave in wall material with the deformation of the chamber wall. The shear waves produce decompression in water and result in the growth of bubble nuclei. Subsequently, those oscillating cavitation bubbles are exposed to the shock pressures, and thus free radicals and rebound shock waves are generated due to their violent collapses. Eventually, marine bacteria around them are inactivated by these productions. In the present study, we investigate the sterilization effects of these oscillating bubbles and cavitation-shock interaction by bio-experiments, respectively. Furthermore, the chemical action of free radicals on marine bacteria is discussed. The generation of the OH radicals is clarified by measuring the concentration of the H2O2. To estimate the generation condition of the OH radicals, a bubble dynamic model consisting of an oscillation model for the growth of bubble nuclei and an impact model to describe the cavitation-shock interaction is developed. Finally, the theoretical estimation by the bubble dynamic model is discussed under the conditions of the present experiments.The phenomenon of cavitation was first discovered in 1894 when the tests were made to determine why a ship could not reach its design speed during sea trials. It was found that the generated cavitation makes the hydrodynamic performance of a propeller reduce, while also give rise to vibration and erosion. After that, cavitation bubbles have been observed in many different fields, and their dynamic behaviors have been studied in detail experimentally, theoretically, and numerically. In experiment, there are some generation methods of cavitation bubbles, such as hydrodynamic method including hydraulic and ultrasonic cavitation, and liquid breakdown induced by laser, electric discharge, or underwater explosion. When local static pressure in liquid decreases rapidly below a limiting pressure, the hydrodynamic cavitation occurs and finally would develop into cloud cavitating flow, such as the flows of hydraulic machinery of pump, screws, and water turbines. The collapse and shedding of the cavitation would bring destructive damage to the machinery (1-4). However, the destruction also has a positive effect with appropriate controlling techniques, in the fields of medical therapy, drug delivery, food engineering, waste water treatment, and so on. Takayama (5) found the liquid jet induced by the motion of cavitation bubble near body stone could enhance the effect of extracorporeal shock wave lithotripsy. These cavitation bubbles were generated in tensile region behind underwater shock wave focusing. For drug delivery, the controlled motion of cavitation bubbles by acoustics were proven to enhance drug activity and uptake when high intensity focused ultrasound was introduced to develop a novel technique of targeting drugs to tumors (6). Song et al. (7) applied a high-power l...

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