Visualization study of gas-liquid two-phase flow patterns inside a three-stage rotodynamic multiphase pump

Visualization experiments were conducted to investigate (under different operating conditions) the gas-liquid two-phase flow patterns at the entry section and the impellers inside a three-stage rotodynamic multiphase pump designed by the authors. A mixture of water and air was selected as the medium. The high-speed photography technology was used to investigate the flow field. The flow pattern presented at the entry section was observed to be bubbly flow. The average diameter of the bubbles increased with the increasing inlet gas volume fraction (IGVF) but decreased with the increasing rotational speed. The flow patterns in the impellers could be classified into four categories with the increasing IGVF. For the tiny IGVF, isolated bubbles flow emerged in all the three impellers. For small values of the IGVF, no obvious gas pocket was observed and the bubbly flow was the main flow pattern in three stages. As the IGVF increased, the gas pocket first appeared in the first stage, while the bubbly flow pattern remained as the main flow pattern in the second and third stages. With further increasing IGVF, the three stages all exhibited as gas pocket flow. The gas pocket originally formed at the suction surface of the blades and then moved to the pressure surface as the gas pocket flowed downstream with the fluid. In addition, some bubbles moved upstream leave the diffuser entrance along the axial direction. Segregated gas flow was observed as the final catagory with the increasing IGVF. The flow pattern maps of the gas-liquid two-phase flow were drawn under different conditions, the ranges of flow patterns extended in the direction of high IGVF with the increasing rotational speed and shrank in the direction of low IGVF with the increasing liquid volume flow rate. With continued increases in the IGVF, the differential pressure of the pump decreased sharply in the range of the gas pocket flow and then decreased smoothly in the range of segregated gas flow.