Experimental study on gas–liquid pressurization characteristics and prediction for critical gas volume fractions of a mixed-flow pump

In the nuclear power system, the gas–liquid two-phase flow appears in the system pipeline when some unexpected situations such as the loss-of-coolant accident (LOCA) occur. Under the conditions of high gas volume fraction (GVF), pumps are prone to pressurization deterioration and even performance failure, which is a serious threat to the operation safety of reactor. In order to reveal the influence mechanisms of pressurization deterioration and performance failure, the gas–liquid pressurization characteristics of a mixed-flow pump (MFP) are experimentally studied. It is found that the critical GVFs of the pressurization deterioration and performance failure of MFP show a U-shaped parabolic variation and an exponential decreasing trend with the increase of liquid-phase flow rate respectively. Increasing the inlet pressure, rotational speed and stage number can improve the overall and inter-stage gas–liquid pressurization performance of MFP, and delay the occurrence of pressurization deterioration and performance failure in the direction of high GVF. The research results show that under different operating conditions, the inter-stage pressure loss ratio increases monotonically with the increase of inlet GVF, and the inter-stage GVF ratio follows the same monotonically decreasing distribution law with the increase of inter-stage pressure ratio. Based on the inter-stage gas–liquid pressurization performance curves, two flow pattern transition boundaries are identified and obtained. The internal relationship between inter-stage gas–liquid pressurization performance and flow patterns is established. The prediction correlations for the critical GVFs of inter-stage pressurization deterioration and performance failure are developed, and the relative errors of prediction for both are within ±10 % and ±8 % respectively. The research results of this paper provide reference and guidance for the operation control and structural optimization of pumps under gas–liquid conditions.