Effect of Air Content on Cavitation Inception as Investigated by Depressurizing Still Water

It has been recognized that air content in water affects inception of cavitation and its development. Number of nuclei in the water which are considered to trigger cavitation, however, has been found to be almost independent of air content, as far as the nuclei are counted by a coulter counter. In this study, the mechanisms of cavitation inception are investigated with emphasis on the role of air content in water. As a result, it is shown that nuclei in water increase with air content when the water is supersaturated with air by depressurization. This was proved by experiments both in atmospheric and reduced pressure conditions. From this study the effect of air content on cavitation may be interpreted as follows: free air bubbles are formed when the water is supersaturated by depressurization and they become nuclei which induce cavitation inception.