PERFORMANCE AND PRESSURE DISTRIBUTION CHANGES IN A CENTRIFUGAL PUMP UNDER 2-PHASE FLOW

Pump performance characteristics change drastically under two-phase fl ow conditions from those of single-phase flow. This is due to a change in flow characteristics in the impeller. Owing to a positive pressure gradient the air bubble moves more slowly than the water in the impel ler channel, but in the suction surface region of the impeller inlet, where a negative pressure gradient prevails, the bubbles move more qui ckly than the water. Thus, in the space just after this region the dis tributions of the void fraction obtained are considerably higher and u neven. The change in the pressure distribution owing to air admission is also particularly evident in the inlet region of the impeller. Thes e changes bring about an alteration of the whole how pattern in the im peller and also cause a drop in pump performance. The Reynolds-average d Navier-Stokes equations for two-phase flow in a centrifugal pump imp eller are solved using a finite volume method to obtain the pressure, velocities and void fraction respectively. Good agreement is achieved when the predicted results are compared with those measured experiment ally within the range of bubbly flow conditions.