Thermodynamic Effect on a Cavitating Inducer in Liquid Nitrogen

For experimental investigations of the thermodynamic effect on a cavitating inducer, it is nesessary to observe the cavitation. However, visualizations of the cavitation are not so easy in cryogenic flow. For this reason, we estimated the cavity region in liquid nitrogen based on measurements of the pressure fluctuation near the blade tip. In the present study, we focused on the length of the tip cavitation as a cavitation indicator. Comparison of the tip cavity length in liquid nitrogen $(80K)$ with that in cold water $(296K)$ allowed us to estimate the strength of the thermodynamic effect. The degree of thermodynamic effect was found to increase with an increase of the cavity length. The temperature depression was estimated from the difference of the cavitation number of corresponding cavity condition (i.e., cavity length) between in liquid nitrogen and in cold water. The estimated temperature depression caused by vaporization increased rapidly when the cavity length extended over the throat. In addition, the estimated temperature inside the bubble nearly reached the temperature of the triple point when the pump performance deteriorated.