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

本研究已经完成，以开发一种替代的淹没水射流系统，该系统在中等低水平的排放压力下运行，并且能够提高通常使用的系统的运行效率和安全性。研究的主要结果如下。（1）发展了在液体中产生微气泡并测量其特性的新实验方法。通过旋转多孔盘将压缩空气注入水中，能够产生直径为10 μ m 40[μm]、数密度为（1 μ 4）× 10^5 [个数/cm ^3]的微气泡，通过新开发的图像处理技术测量。（2）研究了射流出口速度为15 ~ 20[m/s]时淹没射流中空化气泡的产生和发展规律。在射流发展的早期阶段产生的气泡的一个突出特征被发现形成类似于涡环的形状。从摄影数据评价环状气泡的平均轨迹、尺寸和几何形状。（3）采用一种新型的浸没式水射流系统进行了水中有机物的分解实验。结果表明，该系统可以在比现有系统低得多的排气压力下实现有机物的分解。(4)A提出了一种基于双流体模型的淹没水射流数值计算方法。通过考虑在气-液界面处的液体的表面平均压力和跨界面的相变，可以描述在空化气泡破裂时局部高压的发生。

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.