AN INVESTIGATION OF TWO-PHASE FLOW REGIME TRANSITION IN LARGE DIAMETER PIPES

Abstract

<p>The characteristics and flow regime transitions of two-phase (gas/liquid) flow in a vertical large diameter pipe were experimentally investigated. The experiments were performed in a 20cm diameter and 10m long pipe using air and water. The bubble characteristics were measured with a dual-optical probe. Data reduction techniques were developed to estimate the local void fraction, bubble diameter, frequency and velocity. A total of twenty-one flow conditions with superficial air velocity in the range 0.02 to 0.24m/s and superficial water velocity in the range 0.25 to 0.45m/s were investigated. Flow pattern transitions from bubbly to churn flow, without an intermediate slug flow, were observed in the present facility. The bubbly to churn transition occurs at lower superficial air velocities compared to that in small diameter pipes. An empirical transition boundary for bubbly to churn transition is developed for the present experiment. The wall-peak local void fraction and bubble frequency profiles, which are characteristic of bubbly flow in small diameter pipes, were only observed at very low void fraction (〈α〉< 0.04) bubbly flows. The bubbly flow can be classified into undisturbed and agitated bubbly flow according to the bubble motion. The current data is used to evaluate existing drift-flux model correlations for large diameter pipes.</p>