Flow Pattern and Transformation Mechanism of Upward Gas-Liquid Two-Phase Flow in Vertical Tubes Under Undulating Vibration

The flow patterns and transition mechanisms of gas-liquid two-phase flow in vertical tubes under undulating vibration were studied experimentally and theoretically. There are six flow patterns in vertical tubes under undulating vibration, named bubbles flow, mixed flow, slug flow, churn flow, stagnant flow and annular flow and the mixed flow and stagnant flow were found firstly. The flow pattern maps were plotted and the influence of tube diameter, vibration frequency and amplitude on the flow pattern transition boundary were also revealed. The results showed that when the surface velocity of the liquid is fixed, the surface velocity of the gas required to convert the flow pattern from slug flow to churn flow decreases with the increase of the tube diameter, vibration frequency and amplitude, while the gas superficial velocity required to form the annular flow increases. When the gas superficial velocity is constant, the increase in tube diameter, vibration frequency and amplitude make it necessary to need a higher liquid superficial velocity to form the bubble flow. Transition mechanisms were analyzed, and the flow transition boundaries predicted by the transition equations in static and rolling state were compared with experimental data. It was found that the calculated values of the existing models have large errors and are inapplicable to undulating vibration state. By Vibration parameters were introduced and new models applicable to undulating vibration state were established. The average errors of different transition boundaries are 13.24%, 10.3% and 15.25%, respectively.