Flow pattern and pressure drop for oil\u2013water flows in and around 180\xb0 bends

Paul Onubi Ayegba,Nurudeen Yusuf,Lawrence C Edomwonyi-Otu,Abdulkareem Abubakar

doi:10.1007/s42452-020-04031-z

Abstract

Pressure drop and flow pattern of oil–water flows were investigated in a 19-mm ID clear polyvinyl chloride pipe consisting of U-bend with radius of curvature of 100 mm. The range for oil and water superficial velocities tested was 0.04 le U_{{{text{so}}}} le 0.950 ;{text{m/s}} and 0.13 le U_{{{text{sw}}}} le 1.10 ;{text{m/s}}, respectively. Measurements were carried out under different flow conditions in a test section that consisted of four different parts: upstream of the bend, at the bend and at two redeveloping flow locations after the bend. The result indicated that the bend had limited influence on downstream flow patterns. However, the shear forces imposed by the bend caused some shift flow pattern transition and bubble characteristics in the redeveloping flow section after the bend relative to develop flow before the bend. Generally, pressure gradient at all the test sections increased with both oil fraction and water superficial velocity and there was a sharp change of pressure gradient profile during phase inversion. The transition point where phase inversion occurred was always within the range of 0.4 le U_{{{text{sw}}}} le 0.54 ;{text{m/s}}. Pressure losses differed at the various test sections, and the difference was strongly linked to the superficial velocity of the phases and the flow pattern. At high mixture velocity, pressure losses at the redeveloping section after the bend were higher than that at the bend and that for fully developed flows. At low mixture velocity, pressure losses at the bend are higher than in the straight sections. Pressure drop generally decreased with level of flow development downstream of the bend.

Highlights

Co-current flow of oil and water in pipeline is common in chemical, process and petroleum industry operations [1]
Few investigations have been conducted on the co-current flow of oil and water in U-bends with the view of characterising the flow patterns and pressure gradient associated with such flows [12,13,14]
It should be stated that they reported a predominance of core annular flow in their lube–water experiments and an additional flow pattern classified as droplet flow which was absent in the kerosene–water experiments of Sharma et al [14]

Summary

Introduction

Co-current flow of oil and water in pipeline is common in chemical, process and petroleum industry operations [1]. In a separate investigation (with same experimental set-up) using high viscosity oil (lube), Sharma et al [13] reported that the bend as well the direction of flow had significant influence on the downstream flow patterns. Was the flow pattern before and after the bend different for a given flow direction, but it varied from one flow direction to the other This may be associated with the significant difference in viscosity of kerosene and lube oil and the resulting difference in interfacial stress between kerosene–water and lube–water. Pietrzak [12] in their study of oil–water flow in horizontal U-bends categorised flow patterns in terms of the dominant continuous phase (oil dominant, W/O or water dominant, O/W) Their flow pattern characterisation was, limited to the U-bend and did not extend to effects of the bend on downstream flow patterns. High-speed imaging technique was used to capture phase distribution immediately after the bend as well as at the bend and before the bend

Methods

Results

Conclusion