Experimental investigation on the performance of drag reducing polymers through two pipe diameters in horizontal oil–water flows T. Al-Wahaibi a,⇑ , Y. Al-Wahaibi a , A. Al-Ajmi a , N. Yusuf a , A.R. Al-Hashmi a , A.S. Olawale b , I.A. Mohammed b a Department of Petroleum and Chemical Engineering, Sultan Qaboos University, P.O. Box 33, Al-Khoud P.C. 123, Oman b Department of Chemical Engineering, Ahmadu Bello University, Zaria, Nigeria article info Article history: Received 10 September 2012 Received in revised form 22 April 2013 Accepted 30 May 2013 Available online 12 June 2013 Keywords: Oil–water flow Flow pattern map Flow pattern transition Drag reducing polymer Drag reduction Two pipe diameter abstract In this paper, experiments were conducted to understand the influence of a small change of pipe diam- eter in the effectiveness of drag reducing polymer (DRP) in horizontal oil–water flow. Two pipe diameters were used in this study; 19 and 25.4 mm pipes. The results showed a remarkable influence of pipe diam- eter on the polymer efficiency in modifying flow patterns and drag reduction. The results from both pipes showed that only 10 ppm polymer concentration is needed to achieve the maximum drag reduction for each investigated condition. The presence of DRP extended the region of stratified and dual continuous flows. However, the percentage increase in the stratified region is more significant in the 25.4-mm pipe while the extent of the dual continuous pattern in the 19-mm pipe is larger than that in the 25.4-mm pipe. Regardless of the pipe diameter, annular flow changed for all the investigated conditions to dual continuous flow. The dispersed region (water continuous or oil continuous) decreased after introducing DRP but the decrease is larger for the 19-mm pipe especially for dispersion of oil in water. The results for both pipes revealed that the maximum drag reduction is achieved when the flow is dispersed oil in water; however, higher drag reduction was obtained in the larger pipe diameter. Drag reductions up to 60% were observed in the 25.4-mm pipe in comparison with up to 45% achieved in the 19-mm pipe. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction The simultaneous flow of multiphase is a common occurrence during petroleum production operations. Oil–water–gas mixture flowing from wellbore is normally not separated at the well site because it is a very expensive exercise. Hence, for separation, the multiphase mixture is transported to a separation or processing plant through pipelines spanning several kilometres. The presence of many fields would result in hundreds or even thousands kilome- tres of multiphase flow pipelines. Due to these long distances through which the oil–water–gas mixture is travelling, pressure drop in the pipelines becomes significant causing a reduction in production rate and/or an increase in the pumping requirements. Also, turbulence in the flowing mixture results in the formation of oil–water emulsion which makes the separation of phases in the separator and in the storage tanks difficult. Overcoming these challenges can offer considerable economic return and a higher effectiveness in both separation and transportation. It is well known that the addition of a small amount of drag reducing polymer (DRP) can reduce the pressure drop in pipeline. This phenomenon is known as drag reduction (DR). Thus adding a small amount of polymer into the oil–water flow can overcome the aforementioned challenges. Amongst the successes in the applica- tions of DRPs was the use of 10 ppm oil-soluble polymers in the trans-Alaska pipeline system which significantly increased pipe- line flow rates [13]. The effect of drag reducing polymer (DRP) in single phase flow has been the subject of extensive literature (for reviews see [15]). Apart from single phase systems, a number of studies exists on drag reduction in multiphase flow. The majority of these studies have been carried out for two-phase gas–liquid flows (for a com- prehensive review see [5]). Oliver and Young Hoon [16] were one of the first to investigate the effect of DRP in multiphase flows using polyethylene oxide (PEO). Al-Sarkhi and Hanratty [6,7] inves- tigated the influence of a co-polymer of polyacrylamide and so- dium acrylate on annular air–water flow in 9.53 cm ID and 2.54 cm ID pipes. Drag reduction up to 63% was observed in the small pipe while only 48% drag reduction was obtained in the large pipe. The observed drag reduction was attributed to the reduction of interfacial waves which cause drop formation and help the li- quid to spread around the pipe as an annulus. Al-Sarkhi and Solei- mani [8] investigated the effect of DRP on gas–liquid flow in a 2.54 cm ID horizontal pipe. They found a significant change in 0894-1777/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.expthermflusci.2013.05.014 ⇑ Corresponding author. Tel.: +968 95180328. E-mail address: alwahaib@squ.edu.om (T. Al-Wahaibi). Experimental Thermal and Fluid Science 50 (2013) 139–146 Contents lists available at SciVerse ScienceDirect Experimental Thermal and Fluid Science journal homepage: www.elsevier.com/locate/etfs