Estimation of temperature inside unsteady cavitation in high-temperature water

Cavitation is a phenomenon that degrades the performance of fluid machinery, whereas the thermodynamic self-suppression effect of cavitation is prominent in pumps transporting cryogenic fluids because the effect suppresses cavity development. The thermodynamic self-suppression effect is caused by the temperature decreasing inside the cavity by the evaporation and the reduction of saturation pressure inside the cavity; therefore, the cavity temperature is essential to understand the thermodynamic self-suppression effect. The temperature measurement inside the cavity has been limited in the quasi-steady cavitation because it is difficult to accommodate the fast responsiveness of a temperature sensor to respond to the temperature variation of unsteady cavitating flow varying from 10–100 Hz. This study aims to develop the estimation method for the cavity temperature from unsteady temperature response, visualized cavity image, and lumped capacitance model, which is applicable even if the responsiveness of the sensor cannot be increased. The temperature in the unsteady cavitating flow of water at 100 °C and 10 m/s with various cavitation numbers were measured, although the temperature responsiveness was insufficient for the unsteadiness of the cavity. In addition, the phase index, which is the parameter to distinguish the fluid phase around the thermistor, was determined from high-speed video images. The cavity temperature was estimated using the lumped capacitance model with the time variation of the temperature and phase index. As the result of the estimation, the temperature fluctuation of the thermistor and the estimated temperature fluctuation were in general agreement by adjusting the cavity temperature and heat transfer coefficient in the estimation equation. The estimated cavity temperature was smaller than the averaged value and the minimum value of the temperature fluctuation of the thermistor at each cavitation number.