Simultaneous Cavitation Susceptibility Meter and Holographic Measurement of Nuclei in Liquids

Cavitation Susceptibility Meter (CSM) and holographic measurements of cavitation nuclei distributions are compared in this paper. The CSM optically detects cavitation in water samples passed through a venturi. The flow rate, cavitation event rate and upstream pressure are related to the unstable nuclei concentration, as a function of the applied tension, in the fluid. A ruby laser holographic system measured the total nuclei size distribution directly. Microbubbles in the fluid were used as the dominant nuclei source. The data from the two detection schemes were compared by allowing for the dynamical behavior of the bubbles as they pass through the CSM venturi. Both measurements show that the nuclei concentration rises approximately exponentially as the applied tension is increased and then, with further reduction in the pressure, reaches a constant maximum due to the shortage of remaining cavitatable nuclei. The CSM underestimated the concentration of active cavitation nuclei in all the water samples tested. The CSM measured cavitation event rate changes over a range of throat pressures much larger than that predicted using the holographic data. Mutual interference effects between bubbles in the CSM venturi are believed to be partially responsible for this behavior. Attempts to cavitate saturated water of the C.I.T. Low Turbulence Water Tunnel in the CSM were unsuccessful even at the lowest attainable CSM throat pressures. These results bring into question the utility of this CSM concept.