ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT
AZOJETE, September 2019. Vol. 15(3) 792-801

Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria.
Print ISSN: 1596-2490, Electronic ISSN: 2545-5818

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Corresponding author’s e-mail address: uceclce@ucl.ac.uk 792

ORIGINAL RESEARCH ARTICLE

DRAG REDUCTION WITH POLYMER MIXTURES IN PIPES OF DIFFERENT DIAMETERS
M. M. Gimba1., L. C. Edomwonyi-Otu,1,2*., N. Yusuf,3 and A. Abubakar1

(1Department Chemical Engineering, Ahmadu Bello University, Zaria, Nigeria
2Department of Chemical and Petroleum Engineering, Delta State University, Abraka, Nigeria

3Department of Chemical and Petroleum Engineering, Bayero University, Kano, Nigeria)
* Corresponding author’s email address: uceclce@ucl.ac.uk

ARTICLE INFORMATION

Submitted 22 November, 2018
Revised 7 March, 2019
Accepted 10 March, 2019

Keywords:
Drag reduction
Polymers
polymer-polymer mixture
pipe diameter
oil-water flow

ABSTRACT
Transporting crude oil and other fluid in pipelines of different sizes over long
distances in process industries require high amount of energy which results to
high cost of installing pumping stations and maintenance. Addition in part per
million (ppm) of high molecular weight polymeric solution reduce such cost. The
effect of pipe diameter, oil input volume fraction and flow rate (superficial
velocity) on drag reduction (DR) in horizontal oil-waterflows was investigated in
unplasticised polyvinylchloride (uPVC) horizontal pipe with two different pipe
diameters (0.012 and 0.02 m IDs). The two liquids used were diesel oil (ρ = 832
kg/m3, µ = 1.66 cP) and water (ρ = 1,000 kg/m3, µ = 0.89 cP) as test fluids at
ambient conditions (25°C, 1 atm). Partially hydrolyzed polyacrylamide (HPAM;
magnafloc 1011), polyethylene oxide (PEO) and Aloe Vera Mucilage (AVM)
separately, as well as mixture of HPAM-AVM and PEO-AVM at different oil input
volume fraction (δo; 0,0.25, 0.5, 0.75 and 1) and flow rate (Q; 0.65, 1.28, 1.90
and 2.46 m3/hr) were used. The master solution of 2,000 ppm, 2,000 ppm and
20,000 ppm for HPAM, PEO and AVM respectively and their respective mixtures
were used to achieve the required concentrations. Mercury U-tube manometer
was used to measure the pressure drop. DR of 62%, 65%, 54% for HPAM, PEO
and AVM; 69 and 71% for HPAM-AVM and PEO-AVM respectively at mixing
ratio of 3:1 and 1:19 in 0.012 m ID. Also, DR of 58%, 62%, 43% for HPAM, PEO
and AVM; 67% and 68% for HPAM-AVM and PEO-AVM respectively in 0.02 m ID
were obtained at the same condition. The pressure drops observed in the
smaller pipe (0.012 m ID) was higher than that of the larger pipe diameter (0.02
m ID). From the experimental results, DR decreased with increase in the pipe
diameter at the same conditions. This result implies that, DR in oil-water
pipeline flow is a function of oil input volume fraction, superficial velocity and
pipe diameter

© 2019 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved.

1.0 Introduction
The turbulent pipeline transportation of two immiscible liquids (oil-water) is always encountered
in chemical and petroleum industries, which requires large amount of energy because of the
pressure drop experience. Turbulent structures (eddies) of different sizes are formed during the
turbulent liquids pipeline flow, which increase the pressure drop and dissipate pumping energy
(Yusuf et al., 2013; Abdulbari et al., 2014; Edomwonyi-Otu and Angeli, 2014, 2019). The large
decrease in pressure drop by addition of small amount of polymers in parts per million (ppm) is
referred to as percentage drag reduction (DR) (Sellin et al., 1982; Bewarsdorff and Gyr, 1995;
Gimba et al., 2018). One of the first industrial applications of DR was the Trans-Alaska pipeline

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system (1300 km, 1.2 m ID) in 1979, where 10 ppm of oil-soluble polymer was used to increase
the flow rate. Drag reduction of 50 % was achieved, which eliminated the need of installing
additional two pumping stations to boost the throughput from 1.45 to 2.1 million barrel per day.
Other application includes marine and biomedical system, crude oil pipeline transportation over
a long distances, irrigation, floodwater disposal and sewage, drilling of oil from reservoir,
firefighting, Extraction, filtration, heat and mass transfer application (Marmy et al., 2012; Gimba
et al., 2017). It is also now being suggested for transportation of drinking water because of its
harmless properties (Edomwonyi-Otu and Adelakun, 2018).

The parameters responsible for pressure drop in oil-water pipeline flow include pipe diameter,
superficial velocities (mixture velocities), volume fraction of each phase (oil and water), density,
and viscosity of the fluids at constant pressure and temperature (Abubakar, et al., 2015). The
effect of pipe diameter on drag reduction in pipeline flow using drag reducing polymers (DRP)
was studied by many researchers (Lescarboura et al., 1971; Virk, 1975; Interthal and Wilski, 1985;
Ahmad et al., 2009; Karami and Mowla, 2012; Yusuf et al., 2013; Abubakar et al., 2015a;
Edomwonyi-Otu et al., 2016).

Abubakar et al., (2015b) studied the drag reduction on oil-water flow in relatively large pipe
diameter with polymer concentration of 40 ppm and pipe diameter of 0.0747 m ID. Mixture
velocities ranging from 0.1 – 1.6 m/s and 0.05 – 0.9 oil input volume fractions were used. They
compared their results with that of Abubakar et al., (2015a), where they used pipe diameter of
0.306 m ID at the same conditions. Maximum DR of 51% in 0.0747 m ID and 64% in 0.0306 m ID
at oil input volume fraction of 0.05 and mixture velocity of 1.6 m/s were achieved by (Abubakar
et al., 2015b). They (Abubakar et al., 2015b)also concluded that, DR increased with decrease in
pipe diameter. Karami and Mowla (2012) also studied DR of three drag reducing polymers in two
galvanized iron pipes of 0.0254 and 0.0127 m IDs at the same conditions. They also reported
that the drag reduction decreased with increase in pipe diameter for all DRP used. Ahmad et al.,
(2009) investigated the effect of Okra mucilage on DR in different size of pipes (0.015 and 0.025
m ID) in turbulent water flow. They observed that, DR increased (50 – 71%) with decrease in the
pipe diameter (0.025 – 0.015 m IDs) at the same conditions. They suggested that, decreasing the
pipe diameter means increasing velocity inside the pipe, which results to high degree of
turbulence. The high velocity observed in the smaller pipe brings good interaction between the
additive and the turbulent structure (eddies), which subsequently brings about the drag
reduction effectiveness. This agreed with the work of Karami and Mowla (2012). Interthal and
Wilski (1985) were among the first to publish the effect of drag reducing polymers and pipe
diameter on DR. They (Interthal and Wilski, 1985) also reported that DR increased (66 – 80%)
with increase in pipe diameter (0.003 – 0.014 m ID) and then fall to 76% at the highest pipe
diameter (0.03 m ID), showing lack consistency in their results. Lescarboura et al., (1971)
investigated DR in crude oil (single phase) pipeline flow with 8 and 32-inch ID and length of 28
and 32 miles, using polymer concentration of 300, 600 and 1000 ppm respectively. They
achieved DR of 16, 21 and 25% (8-inch ID) and 16, 16.2 and 16.9% (32-inch ID) at the same
conditions. They concluded that DR decreased with increase in pipe diameter and decrease in
velocity.

Despite the available works done in open literature, the influence of pipe diameter on drag
reduction is still scanty. More data were needed to develop models for the accurate prediction
of drag reduction in horizontal oil-water pipeline flow than is currently available. Hence, the
motivation of this work is to provide more data on the study of the effect of pipe diameter on

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Gimba et al: Drag reduction with polymer mixtures in pipes of different diameters. AZOJETE, 15(3):792-801. ISSN 1596-
2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: uceclce@ucl.ac.uk

794

drag reduction in horizontal oil-water flow system using aloe Vera mucilage (AVM), polyethylene
oxide (PEO) and hydrolyzed polyacrylamide (HPAM) as well as their mixture (HPAM-AVM and
PEO-AVM).

2. Experimental Set-Up
2.1 Description of the flow facility
The schematic diagram of the experimental set-up is shown in Figure 1. The flow facility is
divided into: the handling section, pumping or regulating section and test section. The handling
section consists of three tanks where the fluids are stored: the oil, water and separator tanks
have capacity of 200, 200 and 220 liters respectively. The separator tank allows settling under
gravity where water is drain through the bottom opening and the oil is recycled. In the
regulating or pumping section, 0.012 and 0.02 m ID unplasticised polyvinylchloride (uPVC) pipes
are each connected to water and oil tanks. The centrifugal pumps (model Jet 102M/N.31227)
with maximum flow rate of 65 l/min each were used to circulate the test fluids into the test
section. The globe valves were used to regulate the flow rates which were measured with
variable area flow meters (LZM-20J; ±5% accuracy), separate for each fluid. The water flow meter
has maximum flow rate of 100 liters per minute (LPM). The flow meter was calibrated before the
commencement of experiments. The injection port for the polymer master solution is located by
the side of the water pipeline before the Y-junction. The new Era-programmable peristaltic
pump (model NE-9000; ±2% accuracy) was used to inject the polymer master solution into the
water phase. The test section was made up of straight acrylic pipe of 0.012 and 0.02 m ID and
140 times the diameter of the pipe (140D) long from the Y-junction to the second pressure port.
The pressure taps were created by making small holes at the bottom of the acrylic pipe walls at
the distance of 140D which provides fully developed flow in the test section.

Figure 1: Schematics of experimental set-up of flow facility

2.2 Polymer preparation
The polymers used are partially hydrolysed polyacrylamide, HPAM (Magnafloc 1011)
manufacture by BASF chemicals 10 × 106 g/mol, polyethylene oxide (PEO) manufacture by
Sigma-Aldrich with average molecular weight of 8 × 106 g/mol, and Aloe Vera mucilage (AVM)
extracted from Aloe Vera plant. All the polymers are water soluble and were used without further
purification. The polymers solutions were prepared individually first, before the polymer mixture

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solutions were prepared. A master solution of 2,000 ppm of each of the synthetic polymer was
prepared as follows. 10 g of each of the polymer powder was measured using weighing balance
(Kerro, BLC 3002) and gently spread over 5 liters of water surface and stirred for 3 hours with a
mechanical stirrer (Gilverson, L28) at a very low speed (to avoid degradation of the polymer) for
the mixture to be completely homogenized. The stirred solution was left for 12 hours to ensure
complete dissolution of the polymer particles and removal of trapped gas bubbles to form the
master solution (Gimba et al., 2018;Edomwonyi-Otu and Angeli, 2014, 2019). Aloe Vera leaves
were harvested from a garden and washed thoroughly with tap water. The leaves were then cut
vertically on both sides and soaked in tap water for 10 minutes, to remove the Aloin within them.
The leaves were then peeled and the Aloe Vera mucilage (AVM) was extracted by scraping and
sieving the gel from the aloe leaves (Gimba et al., 2017). Aloe Vera leaf contains about 98%
water while the remaining 2 % is the AVM (Bozzi et al., 2007; Davis, 1997). Master solution of
AVM was prepared with 20,000 ppm. For the polymer mixture preparation, the total
concentration (TC) of 30 ppm and 400 ppm for the mixture (HPAM-AVM and PEO-AVM) were
because one of the polymers in the mixture gave maximum DR at that concentration (Reddy and
Singh, 1985). 250 milliliters of 20,000 ppm of AVM master solution was measured and diluted
with 10,000 milliliters of water to achieve 500 ppm.1500 ppm of the synthetic polymers (HPAM
and PEO) was mixed with 500 ppm of AVM and stirred for 3 hours and the stirred solution was
left for 12 hours to form a master solution of 2000 ppm for the polymer mixtures (Reddy and
Singh, 1985; Malhotra et al., 1988). It was injected into the water phase at specific flow rate to
achieve the required concentration in the water flow line.

2.3 Experimental procedure
The flow meters and injection pump were tested before running the experiments to ensure
accurate delivery of the required amounts of oil and water into the test section, and the polymer
master solution into the water phase. The experiment was carried out in horizontal pipe
diameter of 12 mm ID and length of 140 times the diameter of each of the pipe at ambient
conditions (25 °C, 1 atm). The U-tube manometer (Pyrex) was used for the pressure drop
measurement. Each experimental run was repeated three times and the average of the pressure
drop measured before and after the addition of the DRAs. HPAM, PEO, AVM, HPAM-AVM and
PEO-AVM were tested at different oil input volume fraction (δo) and superficial velocity (Us). The
total concentration (TC) of 30 ppm and 400 ppm for HPAM, PEO, Aloe Vera mucilage (AVM) as
well as their mixtures at flow rate of 30 l/min was tested.The optimal polymer concentration (30
ppm for HPAM and PEO and 400 ppm for AVM) and 30 l/min were obtained from our
preliminary single phase water experiments (Gimba et al., 2017 and 2018). The optimal
concentration was selected to be the total concentration (TC) of the polymer mixture (Reddy and
Singh, 1985). The mixing ratio of 3:1 and 1:19 were used. The superficial velocities investigated
range from 0 m/s to 1.68 m/s for 0.020 m and 0 m/s to 4.67 m/s for 0.012 m ID. They superficial
velocity and the oil input volume fraction (δo) was calculated from the Equations 1 - 4. The
pressure drop was recorded and used for calculation of drag reduction as defined by Equation 5;

U =
Q
A (1)

Usw =
Qw
A

(2a)

Uso =
Qo
A (2b)

δo =
Qo

Qo+ Qw × 100% (3)

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Gimba et al: Drag reduction with polymer mixtures in pipes of different diameters. AZOJETE, 15(3):792-801. ISSN 1596-
2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: uceclce@ucl.ac.uk

796

δw+ δo = 1 (4)

DR =
∆PWO − ∆PW

∆PWO
× 100% (5)

Where; � is the average velocity of the fluid in a pipe (m/s),�th and �th are the superficial
velocities of water and oil (m/s). � is the cross-sectional area of the pipe (m), �h and �h are the
flow rate of water and oil (m3/s) and δw and δo are the input volume fraction of water and oil.
∆��� and ∆�� is pressure drop of the fluid without and with DRAs (N/m2).

Table 1: Fluid properties
Density of water, �h at 25°C 1000 kg/m3
Density of diesel oil, �h at 25°C 832 kg/m3

Viscosity of water, �h at 25°C 8.9 × 10−4 Ns/m2

Viscosity of oil, �h at 25°C 1.664 × 10−3 Ns/m2

3.0 Results and Discussion
Only average values of the pressure drop obtained from three measurements were used in the
calculation of percentage drag reduction as well as the viscosity readings. The DR calculated
using Equation (1) was presented graphically against oil input volume fraction and pipe diameter
(Figures 2 to 8).

3.1 Effect of oil input volume fraction, superficial velocity and pipe diameter
The DR of three polymers (HPAM, PEO and AVM) was studied in oil-water flow (Multiphase flow;
MPF) at different oil input volume fractions (δo; 0, 0.25, 0.50, 0.75 and 1), superficial velocities (0,
1.17, 2.33, 3.50 and 4.67 m/s) and pipe diameters (0.012 and 0.02 m ID). Figures 2 - 4 show that,
DR decreased with increase in the oil volume fraction (25 - 75%) due to decrease in the
superficial velocity of the water phase because the DRP used were only soluble in the water
phase. The decreased in superficial velocity of the water phase decreased the turbulent intensity
of the water phase, this results to a decrease in DRP - turbulent eddies interaction and increase
the pressure drop. The pressure drop increase (DR decreased) since the superficial velocity of the
water phase inside the pipe was not enough to stretch the polymer molecules due to the
increase in superficial velocity of the oil phase. This was in agreement with previous reports (Virk,
1975; Yusuf et al., 2013; Abubakar et al., 2014b; Abubakar et al., 2015b; Edomwonyi-Otu et al.,
2015).

In addition, it was observed that at the same conditions, DR increased (58% to 62%; 62% to 65%
and 43% to 54% for HPAM, PEO and AVM respectively) with decrease in the pipe diameter
(0.02 – 0.012 m IDs). The velocity inside the pipe increased as the pipe diameter was reduced,
resulting to a high pressure drop in the smaller pipe diameter, which increased in the degree of
turbulence. The high degree of turbulence in the smaller pipe brings about formation of many
smaller eddies in the water phase due to collisions of larger eddied. The DRP easily overcome
smaller eddies due to lower amount of energy require by the smaller eddies than the larger once.
This corroborate with the findings of Virk, (1975); Interthal and Wilski, (1985); Ahmad et al.,
(2009); Karami and Mowla, (2012). At lower flow rate, the effect of pipe diameter is clearly

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noticeable than at higher flow rate where DR values for 0.012 and 0.02 m are closed to each
other.

Figure 2: Effect of oil input volume fraction on drag reduction at different flow rate and pipe
diameter (0.012 and 0.02 m ID) in oil-water flow for HPAM.

Figure 3: Effect of oil input volume fraction on drag reduction at different flow rate and pipe
diameter (0.012 and 0.02 m ID) in oil-water flow for PEO.

Figure 4: Effect of oil input volume fraction on drag reduction at different flow rate and pipe
diameter (0.012 and 0.02 m ID) in oil-water flow for AVM.

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Gimba et al: Drag reduction with polymer mixtures in pipes of different diameters. AZOJETE, 15(3):792-801. ISSN 1596-
2490; e-ISSN 2545-5818, www.azojete.com.ng

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798

3.2 Effect of oil input volume fraction, superficial velocity and pipe diameter
The percentage DR of two polymer mixtures (HPAM-AVM and PEO-AVM) was studied in oil-
water flow at different oil input volume fractions (0, 0.25, 0.50, 0.75 and 1), superficial velocities
(0, 1.17, 2.33, 3.50 and 4.67 m/s) and pipe diameters (0.012 and 0.02 m ID). Figures 5 - 8 show
that, DR decreased with increase in the pipe diameter (from 0.02 – 0.012 m IDs) at same
conditions. Even though DR decreased due to the increase in oil input volume fraction, the effect
of pipe diameter is clearly noticeable at lower flow rate than at higher flow rate. This corroborate
with the previous findings (Virk, 1975; Interthal and Wilski, 1985; Ahmad et al., 2009; Karami and
Mowla, 2012). Synergism in DR observed for both pipe diameters (0.012 and 0.02 m ID) in the
water phase may be due to the interaction among the polymer molecules, which influence the
extension of the molecules. It may also be attributed to the increase in the polymer coil
dimension and their rigidity. This was in agreement with the work of Edomwonyi-Otu et al.
(2016); Dingilian and Ruckenstein (1974); Reddy and Singh (1985); Malhotra et al., (1988);
Gustavo and Soares (2016) who reported a decrease in drag reduction with increased pipe
diameter.

Figure 5: DR against oil input volume fraction at different flow rate (superficial velocity) and pipe
diameter (0.012 and 0.02 m ID) in oil-water flow for HPAM-AVM at total concentration of 30 ppm.

Figure 6: DR against oil input volume fraction at different flow rate (superficial velocity) and pipe
diameter (0.012 and 0.02 m ID) in oil-water flow for PEO-AVM at total concentration of 30 ppm.

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Figure 7:DR against oil input volume fraction at different flow rate (superficial velocity) and pipe
diameter (0.012 and 0.02 m ID) in oil-water flow for HPAM-AVM at total concentration of 400 ppm.

Figure 8: DR against oil input volume fraction at different flow rate (superficial velocity) and pipe
diameter (0.012 and 0.02 m ID) in oil-water flow for PEO-AVM at total concentration of 400 ppm.

4.0 Conclusion
The effect of pipe diameter, oil input volume fraction and superficial velocity on drag reduction
in oil-water flow has been studied. From the results obtained, it can be concluded that:

DR decreased with an increase in pipe diameter and decrease in the superficial velocity of
the water phase.
DR is a function of oil input volume fraction, superficial velocity and pipe diameter.
Combining HPAM and PEO onto AVM enhanced effectiveness of drag reduction of the AVM.

Acknowledgements
The authors would like to thank the Department of Chemical Engineering, Ahmadu Bello
University Zaria and the members of the Multiphase Flow and Separation Systems Research
Group of the Department, for their moral and technical support.

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