Entropy production analysis of interfacial hydrodynamic instability and gas-pocket evolution in a centrifugal pump

Gas–liquid two-phase flows in centrifugal pumps exhibit severe performance degradation driven by complex interactions among centrifugal forces, adverse pressure gradients, and dynamically evolving interfacial instabilities. This study establishes a generalized entropy production (EP) framework within the Eulerian–Eulerian paradigm to systematically quantify the irreversible energy dissipation mechanisms in a multistage centrifugal pump operating under both single-phase and gas–liquid two-phase conditions. Baseline single-phase analysis reveals that turbulent dissipation (TD), driven by intense shear-layer interactions, dominates EP in the diffuser, whereas viscous dissipation (VD) governs the loss within the impeller. For gas–liquid flows, a generalized theoretical expression for EP that explicitly accounts for interphase momentum exchange, interfacial viscous drag, and turbulent fluctuations of the continuous phase is formulated. The analysis uncovers a critical, previously overlooked loss mechanism: the interfacial VD is strongly coupled with gas-pocket instability at the impeller shroud. Furthermore, as the inlet gas volume fraction increases from 2% to 15%, the dominant dissipative regions undergo a spatial migration from the shroud-side outlet toward the hub-side inlet. Despite the significance of interfacial effects, the TD of the continuous liquid phase remains the paramount contributor to overall EP. These insights advance the thermodynamic understanding of energy degradation in multiphase rotating machinery, providing a theoretical baseline for the hydrodynamic optimization of gas-handling centrifugal pumps.