Thermodynamic Effect on Cavitation in High Temperature Water

Thermodynamic effect on cavitation appears in cryogenic fluids, refrigerant and high temperature water. The thermodynamic effect is considered to suppress the development of cavitation and improve the performance of hydraulic machinery. However, the actual appearance degree of thermodynamic effect depends on not only thermal property of each fluid but also each hydraulic machinery and its operating condition. So, the clarification of the influence of the flow field with unsteady cavitation on the degree of thermodynamic effect is necessary. In order to investigate thermodynamic effect, many experiments had been conducted with using cryogenic fluids or refrigerant as working fluids. However, there are some difficulties to visualize cryogenic fluids and the experimental results cannot be directly correlated to the condition without thermodynamic effect in same fluid. In the present study, in order to conduct cavitation experiments with and without thermodynamic effect in same fluid, high temperature and high pressure cavitation tunnel had been constructed. The working fluid of this tunnel is water and the free-stream temperature can be varied from room temperature to 140 °C. In the present study, NACA 0015 hydrofoil had been chosen as a cavitator. The extent of thermodynamic effect was estimated through the measurement of temperature in the cavity. The temperature was measured by a thermistor probe which has high accuracy. When the thermodynamic effect appears, temperature depression in the cavity is observed. The maximum temperature depression of cavity about 0.3 K had been measured in water of 80 °C.