Investigation on the frictional pressure drop of gas liquid two-phase flows in vertical downward tubes

Abstract Experimental studies on the frictional pressure drop of air-water two-phase flows in vertical downward tubes are conducted in this paper. Experiments are performed at room temperature with the outlet pressure of experimental tube ranging from 0.17 MPa to 0.28 MPa, and four tubes are used with the tube inner diameter being 15 mm, 25 mm, 40 mm and 65 mm respectively. Based on the 978 data obtained in the experiments, prediction performances of 19 existing correlations, which have been developed for predicting the frictional pressure drop of gas-liquid two-phase flow in different tubes, are evaluated to assess the possibility and rationality of using these correlations to predict the frictional pressure drop of gas-liquid two-phase flow in vertical downward tubes as studied in the present paper. The results show that the prediction accuracy of the existing correlations for the frictional pressure drop of air-water two-phase flow in vertical downward tubes decreases remarkably with the increase in tube diameters, and the prediction values are far less than the experiment results under conditions with slug flow and churn flow patterns. It is also found that the buoyancy of bubbles can lead to the increase in the frictional pressure drop of the gas-liquid two-phase flow in vertical downward tubes, especially when big bubbles exist in the two-phase flow. A new model is then established in this paper by introducing a new parameter B into the separated flow model to consider the effect of buoyancy. It is found that in comparison with the existing correlations, the new model can well predict the frictional pressure drop of gas-liquid two-phase flows in vertical downward tubes with higher accuracy.