Analysis of internal flow and energy loss in a LNG cryogenic submerged pump

The liquid natural gas (LNG) submerged pump is the core fluid transportation equipment in the LNG industry. The analysis of energy loss and flow characteristics can improve its performance. In this paper, the flow field is numerically simulated for a LNG cryogenic multistage pump and the energy loss is quantitatively evaluated using entropy generation theory. For each stage, there are significant differences for the energy loss and fluid flow at low flow rates, but they are basically the same except for the first stage when the operating flow rate is greater than 0.8Qd. The higher entropy generation appears in the gap between the impeller and the guide vane. In the first-stage impeller passage and import, the entropy generation is distinctly lower than that in other stages because the circumferential velocity gradient is reduced by the inducer pre-rotation. Meanwhile, as the shear force of the blade on the fluid weakens, the vortex at the first stage impeller can also be decreased. However, it has little effect on the energy loss caused by rotor–stator interaction at the impeller outlet.