Thermodynamic effects at Venturi cavitation in different liquids

Abstract

Thermodynamic effects delay the growth of cavitation bubbles and may accumulate to a considerable level in a bubbly cloud. Under thermo-sensitive conditions, due to thermodynamic effects, a bubbly cloud is often believed to behave similarly to a single cavitation bubble with respect to its shape, oscillation, etc. Discrepancies in thermodynamic effects on cavitating flows in previous experimental studies may result from the lack of control of non-dimensional parameter groups under this special condition. In the present paper, we first derive the non-dimensional parameter groups from the dynamics of a single cavitation bubble traveling through a Venturi tube. Among them, three major non-dimensional parameters are proposed for similitude conditions of Venturi cavitation experiments between different liquids, namely, the thermodynamic parameter, the Reynolds number, and the relative cavitation number. Our theory is validated with systematic experiments of Venturi cavitation in water, Freon 113, and fluoroketone in a small-scale closed-circuit cavitation tunnel under well-controlled conditions. Simultaneous high-speed observations from top and front views provide improved measurement of the cavitation characteristics. By comparing the variations of the attached cavity lengths and their oscillation frequencies, we successfully achieve similarities between different working liquids. The results are of particular importance for surrogates, when the original working liquid is too costly or too hazardous, e.g., cryogenic liquid hydrogen LH2 or liquid oxygen LO2.