Effect Of Rolling Condition On Two-phase Flow Pattern In Vertical Tubes

A variety of flow patterns with different flow characteristic could exist when co-current gas-liquid containing different component flowed through tubes. The characteristic of flow patterns not only depended on the gas and liquid flow rates, pipe structure, pipe layout et al, but also was affected by the state if the device was under the stable condition. So, this dissertation aimed at studying experimentally and theoretically the effect of rolling condition on gas-liquid flow pattern properties in vertical tubes.The experimental research was mainly carried out in a rolling test facility at atmospheric pressure and temperature, and the test section was glass tube, through which the air and water co-current flow and form different flow patterns. During the experiments, it was observed that flow patterns periodically changed during the rolling motion. Depending on pressure differential fluctuation method and visual observation, the onset of bubble flow and annular flow could be decided; Using separated two-phase flow model to make qualitative analysis, and the results showed that the turning point of inside pressure difference curve was just the point where the churn flow took place.Through the analysis of experimental data, it was found that the area of flow pattern was obviously influenced by tube diameter, rolling period and rolling angle, and average void fraction also changed with the vary of mass flow rate, tube diameter, rolling period and rolling angle. Based on the experimental data, the average void fraction correlations of bubble flow, slug flow and churn flow were fitted. Besides, by comparing the average void fraction calculation and experimental data of annular flow, it was found that mixture-single phase model could well predict the average void fraction of annular flow under rolling condition. Based on the analysis of single phase water with rolling motion and experimental research on the effects of Reynolds number, rolling angle and rolling period on single-phase frictional coefficient, a new single-phase frictional coefficient semi-empirical correlation for rolling condition had been proposed. Using this correlation, frictional pressured drop correlations of slug flow, bubble flow and annular flow were also developed, and the calculated results were in good agreement with experimental data, respectively. Moreover, the transition mechanisms between flow patterns under rolling condition were individually analyzed. The Transition criterion correlations of slug flow to bubble flow, slug flow to churn flow and churn flow to annular flow were firstly proposed with the consideration of additional inertia action. By comparing the experimental data, these Transition criterion correlations could be used to predict the transition boundary between flow patterns under rolling condition.Owing to the two-phase flow rate in forced circulation was not changed by the rolling motion, the gas superficial velocity and liquid superficial velocity were chose to be the horizontal coordinate and longitudinal coordinate, and the flow pattern map under rolling condition was drawn, which was hoped to provide some reference in engineering.