Void fraction development in gas-liquid flow after a U-bend in a vertically upwards serpentine-configuration large-diameter pipe

Abstract

We investigate the effect of a return U-bend on flow behaviour in the vertical upward section of a largediameter pipe. A wire mesh sensor was employed to study the void fraction distributions at axial distances of 5, 28 and 47 pipe diameters after the upstream bottom bend. It was found that, the bottom bend has considerable impacts on up-flow behaviours. In all conditions, contour plots of the crosssectional phase distribution measurement using the wire mesh sensor (WMS) show that centrifugal effect of the U-bend causes appreciable misdistribution in the adjacent straight section. However, flow asymmetry significantly reduces at an axial distance of 47D from the U-bend. Flow regime maps generated from three axial locations showed that, in addition to bubbly, intermittent and annular flows, oscillatory flow occurred particularly when gas and liquid flow rates were relatively low. At this position, the mean void fractions were in agreement with those from other large-pipe studies.Comparisons were made with existing void fraction correlations. Among the correlations surveyed, drift flux-type correlations were found to give the best predictive results.

Steady-State Hydraulic Analysis of High-Rise Building Wastewater Drainage Networks: Modelling Basis

“…The experimental evidence suggests that local flow patterns in the vicinity of such junctions are strongly influenced by the junction geometry, but that these influences diminish with distance travelled downstream. Studies on vertical upwards annular flow suggest that pressure gradient and film volume fraction require around 100-300 diameters to develop from an inlet [21], and that flow asymmetry reduces significantly with distance travelled downstream of U-bends [22]. Studies on vertical downwards annular flow indicate sensitivity of flow development processes to inlet junction geometry [23], and also to flow straightener devices which may be inserted to modify a flow profile [24].…”