Evaluating of the effect of the cavitation-vortex interaction on the energy conversion in a two-stage LNG cryogenic submerged pump

Abstract

The quantitative investigation on the unsteady interaction of the thermodynamic cavitation-vortex dynamics has been conducted via the developed entropy production diagnostic model in a two-stage liquefied natural gas cryogenic submerged pump. A thermodynamic cavitation modeling framework and Liutex method are applied to capture the characteristics of the formation, development and collapse of the cavities and vortex. It is found that the increasing flow rate and temperature both intensify the thermodynamic effect of cavitation. As the increase of flow rate, the thermodynamic effect suppresses the growth of cavities, thus raising the maximum temperature drop by 0.65 K at NPSH3% and 0.87 K at NPSH5% with the same temperature. Massive bubbles collapse causes the twist, deformation and breakdown of U-type vortex at the interface, which directly leads to the significant increase of interface entropy production rate in heat transfer entropy production rate (HTEPR). As the increase of temperature, the thermodynamic effect both shortens the cavity size and development period under the same flow rate. The strong shear and rotation regions drive upstream and the pressure rebounds rapidly downstream that weakens the backflow. The shrinkage of upstream cavity and the accelerated collapse of small-scale cloud cavity reduce the HTEPR and viscous flow entropy production rate