Influence of thermal effects on the cavitation of orifices in nuclear power plants

Abstract

Orifices are widely used as throttling devices in nuclear power plants. The pressure drop is not the only driving parameter of cavitation when the fluid is operating at its critical temperature, and the thermal effects cannot be neglected owing to the phase change. This study aims to extend a cavitation model to investigate the impact of thermal effects by modeling the water cavitation flow in an orifice. The thermal effects on the mass transfer process are considered using the Zwart–Gerber–Belamri cavitation model, and the effect of the two-phase flow on the turbulence viscosity is considered in the turbulence model. The numerical results reveal that the period of the variation in vapor volume is shorter under thermal cavitation than under isothermal cavitation. The pressure downstream of the orifice fluctuates with the heat transfer during thermal cavitation. The thermal cavitation model can reproduce the instability downstream of the orifice, which is caused by cavity shedding. The shedding cavities become mushy and frothy during thermal cavitation. The thermal effect term plays a dominant role during vaporization. The influence of thermal effects is positively correlated with the vapor volume fraction, and as the free-stream temperature and velocity increase, the ratio of the thermal effects term to the pressure difference effect term increases during the phase change process.