Cavitation Erosion in a Thin Film as Affected by the Liquid Properties

Abstract

The effect of liquid properties and the atmospheric environment on cavitation erosion was investigated in a thin film cavitation apparatus which consists of an ultrasonic horn with a flat tip vibrating against a stationary 1/2 in. ball at a frequency of 20 KC. The experimental results show that cavitation erosion is less severe for liquids of higher gas solubility or at vapor pressures greater than 100 torr. It is therefore possible to reduce the damage by blending a light component in lubricants or liquids and/or by environmental control. The effect of ambient pressure was also observed by tests in vacuum and under various reduced pressures up to one atmosphere. The damage increases with the increase of pressure. These results indicate that the most important factor in cavitation erosion is the differential pressure inside and outside the cavities, with the dissolved gases and/or vapor serving to control this pressure differential. The investigation of cavitation erosion with liquids of various properties also provides information for the understanding of the erosion mechanism. Evidence was obtained which supports the theory that the damage is caused by fatigue failure attributable to the impingement of liquid jets during bubble collapse. The liquid properties may control the jets velocity and thus affect the applied stress on surface boundaries.