Energy conversion and loss characteristics of multi-stage cryogenic submerged pumps based on power density evolution model

Abstract

Cryogenic submerged pumps (CSPs) are imperative for the efficient transport of cryogenic fluids; however, their multi-stage energy conversion mechanisms remain insufficiently understood under extreme operating conditions. This study aims to quantitatively elucidate the internal flow field and energy transfer characteristics of a two-stage CSP by developing an energy conversion and loss analysis method based on power density distribution. This method integrates high-fidelity numerical simulations and experimental validation using liquid nitrogen. The results reveal that the first-stage impeller is highly sensitive to inlet flow disturbances under off-design conditions, with local flow separation increasing turbulence intensity and energy dissipation; the deviation proportion (DP) in certain channels exceeds 15%. Conversely, the second-stage impeller exhibits a more uniform power density distribution and maintains stable outlet pressure even at 1.4Q_d, where its kinetic energy increment extends to a streamline distance of 0.36 compared to 0.2 in the first stage. Guide vanes account for 65 % of the total turbulent dissipation power and 59 % of wall friction loss, with peak kinetic-to-pressure energy conversion efficiency occurring at a streamline distance of 0.3. Both the impeller and guide vanes exhibit similar energy transfer processes: power density increases slightly at the inlet, decreases gradually along the channel, and rebounds near the outlet. These findings clarify inter-stage synergy and loss mechanisms while providing quantitative design guidance for optimising impeller–guide vane matching, thereby improving overall efficiency and expanding the high-efficiency operating range of multi-stage CSPs.