A Study on the Improvement of Submerged Water Jet Performation by the Efficient Use of Cavitation

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The present study has been done to develop an alternative submerged water jet system which is operated at a moderately low level of discharge pressure and is capable to improve the efficiency and safety in operation of customarily used systems. The main results of the study are as follows.(1)Novel experimental methods were developed to generate micro-bubbles in liquid and to measure their properties. The injection of compressed air into water through a rotating multi-hole disk enabled to produce micro-bubbles with their diameter of 10〜40[μm] and number density of (1〜4) x10^5[number/cm^3] which were measured by a newly-developed image processing technique.(2)The generation and development of cavitation bubbles in a starting submerged water jet were investigated at jet exit speeds of 15〜20[m/s]. A prominent feature of bubbles generated at the early stage of jet development was found to form a shape similar to a vortex ring. The average trajectory, size and geometry of the ring-like bubbles were evaluated from photographic data.(3)Experiments on the decomposition of organic compounds in water were made using a new submerged water jet system where the cavitating water jet was discharged through a specially designed nozzle. The result indicated that the decomposition of organic compounds could be achieved under the discharge pressure much lower than that of currently available systems.(4)A new computational method based on the two-fluid model was developed to calculate submerged water jet flows. By taking into account of both a surface average pressure of liquid at the gas-liquid interface and a phase change across the interface, it became possible to describe the occurrence of locally high pressure at the collapse of cavitation bubbles.