Experimental investigation of the effect of 90° standard elbow on horizontal gas–liquid stratified and annular flow characteristics using dual wire-mesh sensors

Abstract

  Fluid flowing through pipelines often encounters fittings such as elbows. Although it is true that two-phase flow patterns observed in elbows are qualitatively the same as those seen in straight pipes, the presence of a pipe elbow can modify relative positions and local velocities of the two phases as they are subjected to forces in addition to those encountered in a straight pipe. That redistribution can affect pressure drop values, chemical inhibitor concentration and distribution to the top of the pipe, as well as the erosion pattern occurring from solid particles such as sand that is entrained in oil and gas transportation pipelines. In this work, a wire-mesh sensor technique based on conductance measurements of void fraction was applied to investigate two-phase pipe flow through a standard elbow. The horizontal flow test section, consisting of a 76.2 mm ID, 18 m long pipe, was employed to generate stratified-wavy and annular flow conditions. Two 16 × 16 wire-mesh configuration sensors were positioned either 0.9 m upstream or 0.6 m downstream of the bend. The experiments were conducted at superficial liquid velocities equal to 0.03 m/s and 0.2 m/s and superficial gas velocities that ranged from 9 m/s to 34 m/s. The effects of liquid viscosity on the measured parameters are also investigated using two different viscosities of 1 and 10 cP. Stratified–slug transition, stratified wavy and annular flow patterns were observed visually in the clear section placed upstream of the wire-mesh sensors. Analysis of time series void fraction data from the dual wire-mesh sensors allows the determination of mean void fraction, local time average void fraction distribution, liquid phase distribution around the tube periphery, interfacial structure velocities, as well as probability density function characteristic signatures within the cross-section of pipe before and after the elbow. The results indicate that the distribution of gas and liquid phases and interfacial velocities are significantly altered even 20 diameters downstream of the elbow.