泵自吸过程气液两相流的可视化试验

自吸泵的自吸过程属于复杂的气液两相流动过程。通过建立泵自吸性能外特性及自吸过程气液两相流动特性协同测试系统,采用NI虚拟仪器Lab VIEW编程平台,实现了对泵自吸过程中的进出口压力、流量、转速的瞬态测试;同时采用高速摄影观测系统对自吸泵叶轮、蜗壳及气液分离室内部的气液两相流动过程进行了可视化观测。结果表明:在流量未上升之前,自吸离心泵的自吸过程一直处于动态的稳定过程。气液分离室进口出现的稳定气液分离面有利于气液分离,有助于气泡的排出。而扩散段出口出现的停滞回旋气泡不利于气泡的及时排出,对自吸性能有不良的影响。在自吸末期,流量、压力均有突变的过程,且气液分离室内小水珠、扩散管处气泡数目急剧增多,随后又急剧下降,体现了明显的瞬态效应。

Visualization Experiment of Gas-liquid Two-phase Flow of Pump during Self-priming Process

The transient self-priming process is characterized by a complex gas-liquid two-phase flow in the pump, and the gas-liquid mixture and separation effects play a crucial role in gas exhaustion, which further affect the self-priming performance. The collaboration system between the external characteristic of self-priming performance and gas-liquid two-phase flow characteristic during self-priming process was built. Then the experimental instant pump inlet and outlet pressure, pump inlet and outlet flow rate, rotational speed were obtained and programmed by the LabVIEW software. Gas-liquid two-phase flow phenomena in the impeller, volute and gas-liquid separation chamber was observed by high-speed photography system. Results showed that the self-priming process was stable under dynamic conditions before liquid flow was increased. The stable gas-liquid separation interface which appeared at the outlet of the diffuser contributed to gas-liquid separation and gas exhaustion. Bubbles which convoluted at the outlet of the diffuser were not conducive to gas exhaustion in time. During the start-up process, the gas-liquid velocity and the number of bubbles at each section of the volute were in the oscillatory process due to the unstable pressure differential in the impeller. At last instant self-priming process, there was a sudden change in flow rate and pressure. Drops in the gas-liquid separation chamber and bubbles in the diffuser were increased sharply, and then decreased rapidly. The results testified the transient effect during the last instant self-priming process. Microscopic variations of gas-liquid two-phase flow are consistent with macroscopic variations of pressure, flow rate and rotational speed measured by experimental instruments.