Abstract: The gas-liquid two-phase flow field inner a rotodynamic multiphase pump has a direct relationship with the mixed condition of gas and liquid in the entrance. An independent designed buffer tank is installed in front of the multiphase pump and visualization tests are conducted to investigate the flow pattern of gas-liquid two phases and the distribution rule of bubble size in different conditions of rotational speed and inlet gas volume fraction (IGVF). The test results show that the flow pattern of the gas-liquid two phases is presented as uniform bubble flow after the mixture passing through the buffer tank and there is no aggregation of big bubbles, which can verify the rationality of the designed structure and the opening scheme on central porous pipe of the buffer tank. More importantly, the buffer tank has the ability to well mix the gas and liquid. From the analyses of bubble sizes, a normal distribution of them can be seen. With the increase of IGVF (0-50%), the gas volume flow rate increases and then the initial bubble size increases, which cause the bubble size also grows in the entrance when the rotational speed and liquid volume flow rate are constant. When the IGVF and liquid volume fraction are constant, the initial bubble sizes keep constant too. However, with the increase of rotational speed (1 800-2 700 r/min), the drag force between liquid and gas increases correspondingly, which causes bubble sizes decrease. In addition, curves are drawn to express the relationships of bubble size with IGVF and rotational speed, which will provide theoretical support for the setting of inlet boundary conditions to simulate the inner flow of the multiphase pump.

Key words: buffer tank, flow pattern, gas-liquid two-phase, visualization test