Investigation on mechanism of critical cavitating flow in liquid jet pumps under operating limits

Abstract

a b s t r a c tThe critical cavitating flow in liquid jet pumps under operating limits is investigated in this paper. Measurements on the axial pressure distribution along the wall of jet pumps indicate that two-phase critical flow occurs in the throat pipe under operating limits. The entrained flow rate and the distribution of the wall pressure upstream lowest pressure section does not change when the outlet pressure is lower than a critical value. A liquid-vapor mixing shockwave is also observed under operating limits. The wave front moves back and forth in low frequency around the position of the lowest pressure. With the measured axial wall pressures, the Mach number of the two-phase cavitating flow is calculated. It's found that the maximum Mach number is very close to 1 under operating limits. Further analysis infers a cross-section where Mach number approaches to 1 near the wave front. Thus, the liquid-vapor mixture velocity should reach the local sound velocity and resulting in the occurrence of operating limits.

Experimental investigation on liquid absorption of jet pump under operating limits

“…6(a), which is similar to the liquidegas mixing shockwave proposed by Witte and Brennen [25,26]. The interface wave is instability and moves forward and backward [27], crossing which the density, velocity and pressure change sharply. Hence, there is a great pressure gradient VP appearing when the interface wave passes.…”

Cavitating flow in annular jet pumps

“…In our previous studies, pressure coefficient distribution (C p ) is suitable to describe the inner flow details, especially when cavitation appears (Long et al, 2009). In this study, by monitoring C p , the cavitation state and the development of vapor cloud were obtained.…”

“…Hence the inception of cavitation in CJP can be due to high shear and vortex in jet boundary (namely shearing layer). However, Long et al (2009) pointed out that adverse pressure gradient caused by the convergent suction chamber was another reason for cavitation occurrence.…”

Experimental investigation of the propagation characteristics of an interface wave in a jet pump under cavitation condition

“…It was found that the sound velocity decreases sharply as the gas fraction increases, declining to only 25 m/s at a high gas fraction. Long et al [15] investigated the critical cavitation flow in the jet pump and observed a liquid-vapor mixing shockwave. The wave front moves back and forth around the lowest pressure point at a low frequency, while the pressure fluctuation and propagation rule of the wave are not mentioned in further study.…”