Development of Cavitation Nuclei Distribution Measuring Equipment

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The cavitation nuclei distribution measuring equipment which has a high mobility has been developed. Cavitation nuclei are measured by a light scattering method. This equipment has the following feature: (1) Microbubbles are able to be distinguished from solid particles in the liquid. (2) Cavitation nuclei are measured directly in the liquid. (3) Measurement and data treatment can be done in real time.Preceding the development, the scattered light intensities are calculated using the Mie's theory. The collecting efficiency of the scattered light and the detected light intensity in the control volume are estimated in various alignments of optical parts. According to these calculations, the scattered light is detected from two directions ( <theta> , <phi> )=(90, <-!+> 15). The laser light incidents into the control volume from the direction of ( <theta> , <phi> )=(0,90), and the flow enters into the control volume from the direction of ( <theta> , <phi> )=(90,0). The light scattered from … More a microbubble is not detected correctly due to not only the nonuniformity of the light intensity but also the distorted image of the microbubble on the aperture. In order to estimate the accuracy of the system, a Monte Carlo simulation is employed, where the size of nuclei and the location within the control volume are determined randomly. This simulation reveals that 5000 data are required to obtain reliable data.The equipment is divided into four parts, i.e. light source, probe part which is installed in a cavitation tunnel, photo detector and data processor. The light source, the probe and the photo detector are connected by the optical fibers, which improved the mobility. The two detected lights from the microbubble are collected when the two signals observed at the same time. The collected two signals are compared each other and the signals are recognized as the scattered light from a microbubble only when the signals coincide within from 200% to 50%.The measuring system is tested in a cavitation tunnel and the reliability of the system is confirmed. Less