Numerical analysis of entropy production on a LNG cryogenic submerged pump

Abstract

LNG cryogenic submerged pumps are the core component of LNG terminals and filling stations for mass transmission. A deep understanding of hydraulic behavior in LNG cryogenic submerged pumps is helpful to improve their performance. However, traditional analysis of hydraulic losses lacks intuitiveness. In this study, the irreversible energy loss was investigated based on entropy production theory, focusing on the magnitude and position of hydraulic loss of a two-stage LNG cryogenic submerged pump. Subsequently, a 3D steady flow field with a Reynolds stress turbulence model and energy equation model was conducted, and a UDF was used to calculate the entropy production. The results indicated that entropy production theory had advantages for evaluating the energy characteristics of the LNG pump. Turbulent dissipation and wall friction were considered to be the primary sources of generating irreversible hydraulic loss. Turbulent entropy production and wall entropy production accounted for approximately 73.25%–77.48% and 22.49%–26.72% of the entire production, respectively. At a 1.0Qd flow condition, STD and SW were 73.51% and 26.46%, respectively. The impeller at the second stage and guide vanes at the two stages (greater than 40 W/K) were the hydraulic loss domains, and the volumetric entropy production rate in impeller of the second stage was extremely high (average 10 000 W/m3K). The separation flow, shock phenomenon and vortex were considered to be hydrodynamic factors for the formation of entropy production. This research indicated that the entropy production theory can help to quantify irreversible energy loss and locate where and how it occurs, and even further to optimize pump performance.