Numerical study of gas pocket distribution and pressurization deterioration mechanism in a centrifugal pump

Abstract

In the event of a loss-of-coolant accident at a nuclear power plant, a large amount of steam enters the main pump, causing the pump's pressurization to deteriorate or even fail. To reveal the deterioration mechanism of the pump performance, the gas-liquid distribution characteristics in the centrifugal pump were studied by using structured grids and the Eulerian-Eulerian model. Based on the dimensional analysis method, a predictive correlation for bubble size was established, which included factors such as inlet gas volume fraction (IGVF), rotational speed, liquid flow rate, and impeller geometric parameters. When the predictive correlation is applied to the numerical simulation, the numerical two-phase pressurization agrees well with that obtained from the experiment. As the IGVF increases, the gas begins to accumulate at the impeller inlet under the effect of the pressure gradient force. Due to the large increase in liquid velocity, the gas begins to accumulate from the middle of the diffuser flow channel. The area occupied by the gas pocket in the impeller loses its pressurization capability. The pressure vortex formed at the inlet of the channel causes the diffuser to lose its pressurization capacity. An increase in rotational speed and a decrease in liquid flow rate can effectively prevent the formation and development of gas pockets in the impeller.