Effects of reflux-hole position on gas–liquid separation and self-priming performance in a vortex self-priming pump

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This study investigates the influence of reflux-hole height on self-priming performance in a vortex self-priming pump. Three-dimensional transient simulations were performed using an Eulerian volume-of-fluid model, and Liutex-based vortex identification and local entropy production analysis were employed to reveal the coupling between vortex structures and irreversible energy loss. The baseline pump without a reflux hole serves as the reference case. Results show a distinctly non-monotonic effect of reflux-hole height: a low-position hole (58 mm) increases the inlet gas mass flow rate by 41% relative to baseline and reduces the self-priming time from 2.35 to 1.65 min, whereas intermediate heights (88–99 mm) degrade performance due to back-pressure accumulation, liquid-ring discontinuity, and blockage vortices. The optimal high-position hole (114 mm) achieves a 62% increase in gas mass flow and shortens self-priming time to 1.45 min. Entropy production analysis indicates that turbulent dissipation dominates energy loss, with severe irreversible loss arising mainly from shear-dominated deformation around vortex boundaries rather than rigid-body rotation. Within the tested pump geometry and operating conditions, intermediate reflux-hole heights should be avoided, while a high-position reflux hole near the gas-discharge side maximizes gas evacuation and minimizes nonproductive energy dissipation.