Two-phase flow in diffusers is often accompanied by pronounced gas accumulation caused by low-pressure regions associated with flow separation, leading to a deterioration in pressure recovery. This behavior poses a major limitation to the performance of centrifugal pumps operating under gas–liquid flow conditions. Compared to rotating pump components, diffusers provide a simplified and well-controlled environment, making them particularly suitable for detailed experimental investigations. In this study, the influence of surface geometry modifications on gas accumulation is examined by introducing grooves and bars of different sizes on the upper wall of a diffuser. These structures are intended to enhance local turbulence and promote gas dispersion in regions prone to accumulation. A diffuser with a gradually increasing opening angle was designed to deliberately trigger flow separation and gas entrapment. The two-phase flow behavior was analyzed using high-speed visualizations to capture the interaction between gas and liquid phases under various operating conditions. The results show that small-scale grooves and bars have only a marginal effect on mitigating gas accumulation. In several cases, these modifications intensify flow separation, leading to increased gas hold-up, particularly at low liquid flow rates combined with high gas flow rates. In contrast, larger bars, especially the largest tested configuration, demonstrate a pronounced ability to reduce gas accumulation, most notably at higher liquid flow rates. The findings provide valuable experimental insight for validating numerical models and offer practical guidance for geometric optimization aimed at improving centrifugal pump performance under two-phase flow conditions.
Mansour et al. (Mon,) studied this question.