On the influence of thermal phenomena during cavitation through an orifice

Abstract

Thermal properties of cryogenic fluids can profoundly change the nature of cavitation since the fluid pressure drop is not, anymore, the only driving parameter of this phenomenon.In this research, we have conducted experiments inducing cavitation via a cylindrical orifice using Liquid Nitrogen as working fluid and exploring cavitation regimes going from bubbly cavitation to full flashing. Among others, we performed unsteady pressure measurements to derive the speed of sound during cavitation and high-speed imaging to understand the evolution of the two-phase flow along the pipe.In our analysis we use five dimensionless numbers to describe the flow conditions upstream and downstream of the orifice, and the type of transition taking place across the orifice.In this paper, we show that the fluid initial subcooling level ΔTsub upstream of the orifice and the superheat level Rp of the flow downstream of the orifice are two parameters essential to take into account the metastability of the fluid. Therefore, we propose a new semi-empirical model for predicting the effect of the fluid thermal properties on cavitation. Specifically, we define a parameter T which, multiplied by the saturation pressure at the inlet temperature, allows us to estimate the pressure reached at the orifice to cavitate.