Investigating the Behaviour of Two-Phase Vertical Upward and Downward flows in Large Diameter Pipe

Abstract

The understanding of the behaviour of vertical upward and downward two-phase flow in large diameter pipes is very important in chemical, petroleum and nuclear sector where safety is of utmost concern. This work helps to add to the little research done on vertical downward flow in large diameter pipes as compared to numerous works done in vertical upward flow. This work analysed the experimental results obtained from using a conductance ring probe of the void fraction measurements done on air-water flow in 127mm diameter pipe for vertical upward and downward. A gas superficial velocity (USG) and liquid superficial velocity (USL) ranges from (3.45-16.05) m/s and (0.02-0.2)m/s respectively. Annular flow regime was identified in vertical upward and downward flow with the use of the probability density function (PDF), time series of average void fraction and Sholam’s flow pattern map and the result was compared with previous studies. The analysis of the 15000 data points for the 17 runs for the upward and downward flow showed tendency in the effect of void fraction and dominant frequency with varying flow rates. The differences in the behaviour of the vertical upward flow and vertical upward flow observed were as a result of the gravity, buoyancy and interaction of the liquid inertia. Using the drift flux model, the linear relationship between the gas actual velocity and mixture velocity was established for both pipe orientations for USL of (0.02-0.2)m/s to give the distribution parameter (Co) and drift velocity (UGM).The available drift-flux models developed for vertical upward flow can be equally used for downward flow by changing the sign of the drift velocity from positive to negative. The result of the top 10 drift-flux model correlations and the one derived from momentum equation for falling film/annular flow available for upward flow and downward flow to predict the void fraction were used and compared to the one in this work to check for the percentage error and RMS error.