Experimental and theoretical study on the association between entrainment vortex evolution and pressure oscillation of steam jet condensation

Abstract

Condensation pressure oscillation of steam jet has great influence on direct contact condensation (DCC) equipment. Therefore, it is essential to reveal the microscopic mechanism of pressure oscillation of steam jet condensation. In this study, the association between entrainment vortex evolution and pressure oscillation of steam jet condensation is investigated. Firstly, the periodic variation of characteristic parameters of jet oscillation caused by periodic vortex shedding is obtained based on the image processing techniques. Secondly, by synchronous comparison between the pressure oscillation cycles and the jet parameters oscillation cycles, it is found that the periodic evolution and shedding of two-phase entrainment vortexes formed in the upper and lower mixing layers is the microscopic mechanism which causes condensation pressure oscillation. Specifically, the high-frequency pressure oscillation near the steam jet results from the high-frequency transverse oscillation of the steam jet which is caused by the periodic vortex evolution in the mixing layer and the periodic shedding of the vortex blob at the tail of the jet; the low-frequency pressure oscillation near the steam jet results from the low frequency oscillation of the whole steam jet caused by periodic shedding of the paired vortex blobs; the pressure oscillation in the downstream of the steam jet is caused by the condensation oscillation of periodic shedding vortex blobs. Finally, the dominant frequency distribution of condensation pressure oscillation under various test conditions is analysed. Combined with the vortex shedding model, a prediction equation of the dimensionless characteristic frequency St of the shedding vortexes is established. The predicted values had good agreement with the experimental results.