Fluid Dynamic clarification of Bubble Generation Phenomena in Human Body under the Decompressed Environments

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Submarine sickness is taken ill with vesication in dived human body, however very little is known about the dynamic mechanism of the sideration yet. The purpose of this report is to study experimentally and theoretically the bubble generation in human body from a viewpoint of fluid dynamics. First, the apparatus about bubble formation in liquids with pressure variation was manufactured for trial, which used to model for the environmental conditions in deep sea. By making the experiment applied this apparatus, it is found that the bubble density in liquid becomes high with increasing the decompression in the pressure vessel, and that the tendency is noticeably with an increment of the maximum additional pressure. As carbon dioxide was dissolved in liquid, the bubble densities in the liquid are three-quintuple times as compared with air, and some relatively large spherical bubbles with about 2mm in diameter are observed. For dissolved air, the spherical bubbles whose radii are about 1mm appear in the decompressed liquid. Cavitation phenomena around a high-speed rotating disk were studied in water and human blood. In blood, cavitation occurs at lower Reynolds number than in water. The cavitation noise level in blood is higher than in water. Numerical calculations were conducted by combination of the equation of motion for a bubble and the diffusion equation of gas. As a result, the bubble growth rate increases with the elapsed time, and the maximum radius of the bubble is large with the depth in sea. Small bubbles are affected by gas diffusion, consequently the growth rates of bubbles become large.