An experimental study on air entrainment in a suction sump over critical-submergence condition

In pump's sumps, the air entrainment sometimes occurs. In various industrial and environmental problems, the air entrainment often induces vibration, noise, low pumping efficiency or pump's collapse at the worst. The present aim is to understand the air entrainment appearing inside a simple and basic suction sump in the vertical-wet-pit-pump configuration. In particular, we focus upon the influences of governing parameters upon the occurrence-time ratio r of the air entrainment, using a conductance-type electric sensor which can detect the existence of air bubbles through a suction pipe with no disturbances by the sensor probe and with a fine spatial resolution in order to achieve accurate measurements. As a result, we reveal the influences of the Froude number, the Reynolds number, the Weber number (or the Bond number) and three geometric parameters upon the air entrainment in over-critical-submergence condition.