Enhanced quantitative methodology for energy loss analysis and its application to transient annular vortex of an annular-casing nuclear reactor coolant pump

This study proposes and applies a novel enhanced methodology for quantifying energy loss, aiming to more accurately analyze the characteristics of a newly discovered annular vortex within the annular casing of a nuclear reactor coolant pump (NRCP). The results show that turbulent entropy production dominates, contributing 59.09%, while direct entropy production accounts for 40.91%. Using the proposed formulation, the energy loss attributed to the annular vortex is quantified and found to represent 85.497% of the total loss. In comparison, the kinetic energy retained by the fluid inside the casing accounts for 13.49%, and the remaining 1.013% is associated with other small-scale vortex structures. A new dimensionless number—the energy loss coefficient—is introduced to characterize local energy loss intensity. This coefficient, combined with the pressure fluctuation coefficient, enables a joint analysis of energy loss distribution, revealing that the bottom of the casing experiences the most significant energy dissipation. These findings provide theoretical insight into the internal energy distribution and loss mechanisms within the NRCP casing and offer technical guidance for its future optimization.