ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT
AZOJETE, June, 2019. Vol. 15(2):248-258

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

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248

ORIGINAL RESEARCH ARTICLE

ALOE VERA MUCILAGE AS DRAG REDUCING AGENT IN OIL-WATER FLOW
M. N. Abdallah1, L. C. Edomwonyi-Otu1,2*, N. Yusuf3, and A. Baba1

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

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

ARTICLE INFORMATION

Submitted 2 September, 2018
Revised 19 February, 2019
Accepted 19 February, 2019

Keywords:
Drag Reduction
Natural DRAs
Aloe Vera
Oil-Water Flows

ABSTRACT
Drag reduction is the deliberate reduction of the frictional pressure drop
in flow systems by the addition of heavy molecular weight polymeric
materials as well as other means such as pipeline modifications.
Environmentally friendly and cheaper heavy molecular weight polymeric
drag reducing agents (DRAs) has become a necessity in the
transportation of fluids particularly in the oil and gas industry. However,
very few reports exist on the potentials of natural polymers such as
extracts from the Aloe Vera plant. In this study, the effects of Reynolds
number and polymer concentration on the drag reduction effectiveness
of Aloe barbadensis miller were tested. An experimental flow facility using
unplasticized Polyvinylchloride (uPVC) pipe of 12 mm ID was constructed
with diesel (density = 832 kg/m3, dynamic viscosity = 1.664 mPa.s at 25°C)
and water (density = 1000 kg/m3, dynamic viscosity = 0.891 mPa.s at
25°C) as test fluids. Drag reduction as a function of Aloe polymer
concentration in the range 50 ppm to 500 ppm and Reynolds number
20000<Re<90000 were investigated by comparing the U-tube
manometer pressure drop readings with and without aloe polymer. The
pressure drop difference expressed as a percentage of the pressure drop
without aloe polymer is termed drag reduction and was used to
demonstrate the effectiveness of the Aloe Vera extracts or polymer as a
DRA. In single phase horizontal (water) flow, a maximum drag reduction
of 64% (U = 4.67 m/s) was measured, while in multiphase horizontal flow,
a maximum drag reduction of 53.80% (α = 25%, Um = 4.67 m/s) was
measured. Furthermore, measurements showed that pipe inclination had
minimal effect on the drag reduction achieved. It was deduced that Aloe
Vera mucilage can be used as a drag reducing agent in oil-water flows for
Reynolds number below 63,000.

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

1.0 Introduction
One of the major operations in the process industry is the transportation of fluids along
pipelines. It has been shown that frictional drag between the fluids and pipe wall causes
substantial pressure drop along the pipelines (Al-Wahaibi and Angeli, 2007; Edomwonyi-Otu,
2015). Today, pumping systems constitute 20% of the world’s electrical energy demand and
consumes 20-50% of the energy usage in certain industrial plant operations (Hameed, 2014).
Hence, the importance of drag reduction cannot be overemphasized. Drag reduction generally

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refers to a process where the frictional pressure drop within a piping system is deliberately
reduced thus significantly reducing pumping energy required (Manfield et al., 1999; Edomwonyi-
Otu and Angeli, 2014; Edomwonyi-Otu, 2015). The relevance for practical applications is thus
enormous (Edomwonyi-Otu and Adelakun, 2018). Savins (1964) was the first to use the term
“Drag Reduction” with the definition:
DR = ∆Psolvent−∆Ppolymer

∆Psolvent
X100 (1)

where: ΔPpolymer and ΔPsolvent (N/m2) signify the frictional pressure drops in the presence
and absence of drag reducing polymers respectively.
Drag reduction can be carried out via several methods including the use of drag reducing agents
(Edomwonyi-Otu and Adelakun, 2018). Drag reducing agents are added to the flow in order to
reduce frictional drag and can be categorized as: polymers, surfactants, fibers, micro-bubbles
and compliant coating. This research however is limited to the use of natural polymers as drag
reducing agents in oil-water flow. The first documented work on oil-water flow was carried out
by Al-Wahaibi and Angeli, (2007). They investigated the effects of Magnafloc 1011 (a co-polymer
of polyacrylamide and sodium acrylate) on the pressure drop and flow patterns of oil-water
flows in a 14-mm ID horizontal acrylic pipe. They reported a maximum drag reduction of 50%.
Yusuf et al., (2011) also investigated the effect of a DRP (Drag Reducing Polymer) on pressure
drops using a mineral oil in a 25.4 mm ID. They noted that drag reduction showed an increase
with the polymer concentrations. They reported a maximum drag reduction of 60% in oil-water
flow.
Recently, Edomwonyi-Otu (2015), Edomwonyi-Otu et al. (2015), and Edomwonyi-Otu and Angeli
(2019) investigated the effect of DRP on oil-water mixture in a horizontal 14-mm ID acrylic pipe.
They used low concentration of solutions of partially hydrolysed polyacrylamide (HPAM, 8 x 106
g/mol.) and two types of PEO (5 x 106 and 8 x 106 g/mol.) and as drag reducing agents. The
changes that occur to Reynolds stresses with polymer addition were studied with particle image
velocimetry (PIV) technique. The addition of 20 ppm of HPAM resulted in DR of 80% in water
flows as well as 52% in oil-water flows. In addition, the turbulence properties (velocity profiles
and Reynolds stresses) as well as the interfacial wave characteristics of the flows were affected by
the polymer addition. Higher molecular weight polymers gave better DR owing to their better
ionic strength and resistance to mechanical degradation. Their reports supported the proposed
mechanism of drag reduction that suggests that turbulent kinetic energy of flows is redistributed
with addition of polymeric solutions.
Abubakar, (2016) worked with an anionic copolymer of polyacrylamide and 2-Acrylamido-2-
Methylpropane Sulfonic acid in a 30.6 mm pipe ID, using an inclined pipe orientation. He
reported 64% drag reduction for horizontal oil-water flows. Positive inclination led to 3.3%
improved drag reduction (when compared to horizontal flow), while negative inclinations had
mixed results; varying between increased and decreased drag reduction when compared to
horizontal flow. A general problem encountered in drag reduction studies is the fact that though
many mechanisms of drag reduction have been brought forward (Al-Sarkhi, 2010; Manfield et al.,
1999; Mowla and Naderi, 2006; White and Mungal, 2008), none have been universally accepted.
Lumley (1973) postulated that the increased extensional viscosity due to the stretching of
randomly coiled polymers tends to dampen the small eddies in the buffer layer and thickens the
buffer layer, to give rise to the drag reduction. Conversely, De Gennes (1990), criticized the

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Abdallah, et al: Aloe Vera Mucilage as Drag Reducing Agent in Oil-Water Flow. AZOJETE, 15(2):248-258. ISSN 1596-
2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: uceclce@ucl.ac.uk 250

earlier extensional viscosity postulate. He went on to argue that the elastic energy stored in the
macromolecules are responsible for drag-reduction.
Reports in some extant literature suggest that mucilage, a viscous substance found in plants,
exhibits drag reducing properties. Lim, (2010) used extracts from Malabar Spinach in a 25.4 mm
pipe ID and achieved 78.2% drag reduction in single water flow. Abdulbari (2011) studied the
effects of Aloe Vera mucilage in single phase flow and achieved a maximum drag reduction of
63% in a 25.4 mm pipe ID. However, reports studies using natural polymers in oil-water flows are
generally unavailable There is therefore a need to explore this system in order to generate more
data on drag reduction using natural polymers in oil-water flows. This will give insight on the
extent of drag reduction that can be achieved using natural polymers in oil-water flows. Hence,
this research aims to determine the effectiveness of Aloe Vera mucilage, a natural polymer, in
oil-water flow.
Natural DRAs also offer a biodegradable alternative to the synthetic polymers currently being
used. This study aims at determining the effectiveness of Aloe Vera mucilage as a drag reducing
agent in multiphase flow.

2. Experimental Set-Up
The experimental set-up was designed and fabricated at the Chemical Engineering Department
of the Ahmadu Bello University Zaria, Nigeria. A schematic diagram of the experimental set-up is
shown in Figure 1.
2.1 Polymer Preparation
Aloe Vera leaves were cut from the base of the plant and washed thoroughly. The leaves were
then cut vertically on both sides and soaked in water for 10 minutes, to remove the Aloin (bitter,
yellow residue) within them. The leaves were then peeled and the Aloe Vera mucilage was
extracted by scraping the gel from the aloe leaves and pressing on a No. 4 (4.75 mm) sieve. Aloe
Vera leaf contains 98% water Davis, (1997) while the remaining 2% is the active Aloe Vera. This
was carried out in the chemical engineering laboratory of the Ahmadu Bello University, Zaria,
Nigeria. The 20,000 ppm master solution was then used immediately after preparation. A
polymer injector pump (New Era Model No. NE-9000; ±2%) was used to introduce the polymer
solution into the test section. A material balance was used to achieve the required concentration
in the water phase.

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251

Figure 1: Schematic representation of the experimental flow facility for drag reduction

2.2 Experimental System
The experimental system consisted of two buildup tanks (for water and diesel respectively), with
capacity of 200 liters each. Two 1-horsepower surface pumps. 0.012 m ID unplasticized
polyvinylchloride (uPVC) pipes. A U-tube manometer. Globe and Gate valves and two (LZM-20J;
±5%) flowmeters, with capacities of 60 L/min. The U-tube manometer (Pyrex) was used to detect
the pressure drop and the flow meters, used to regulate the flow rate of fluid passing through
pipes.
From each of the storage tanks, a centrifugal pump was used to transport the fluid to the testing
section. Each flow line was fitted with a flow meter and a gate valve. The flow meters, with two
globe valves attached for regulation, were calibrated before use. The fluids were brought
together via the use of a smooth Y-junction (at an angle of 45°), which minimized their mixing.
The design was such that the diesel entered from the top and the water from the bottom before
reaching the testing area. The prepared drag reducing agent was injected using a new Era-
programmable peristaltic pump (model NE-9000; ±2%) before the point of mixing, into the
water phase.
The test section comprised of 0.012 m ID uPVC pipe, a 1m long acrylic view section with two
pressure ports located 0.5 m apart and a U-tube manometer connected via rubber tubing to the
pressure ports. The first pressure port was located 3.0 m from the mixing point; well in excess of
the recommended 150 times the diameter of the pipe used (Lien et al., 2004). This is to allow for
fully developed turbulent flow before pressure drop readings were taken. Aloe Vera mucilage
concentrations, ranging from 50 ppm to 500 ppm were used. Also, several Reynolds numbers
were used (by varying the input flowrate), with a maximum Reynolds number of 83,690.20
investigated for the single-phase experiments. For the multiphase experiments, oil (diesel) was
introduced to the system at different concentrations. A mixture velocity (Umix) range of 4.67 to

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Abdallah, et al: Aloe Vera Mucilage as Drag Reducing Agent in Oil-Water Flow. AZOJETE, 15(2):248-258. ISSN 1596-
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1.11 m/s was used and oil input fraction ranged from 0 to 1. In the single-phase experiments, an
optimal concentration of the DRA was observed and recorded (the point at which further
addition of the DRA did not yield an increase in the observed drag reduction). The
concentrations and flowrate at which the optimum drag reduction was achieved in single phase
was adopted for the multiphase experiments. DRA concentrations higher and lower than the
optimal, were used to confirm if the drag reduction would change, thus changing the optimal
concentration for multiphase flow. The drag reduction in both cases showed no change, thereby
confirming the optimum DRA concentration in single-phase and multiphase to be the same. The
optimal flowrate from the single-phase was also used to determine the optimal velocity. This was
then used to determine the mixture velocity for the oil and water in the multiphase experiments.
The separator, with a capacity of 220 liters, was used to recover used diesel; which was then
recycled to the diesel buildup tank. This separation was done using the differences in density
between the testing fluids (Helmenstein, 2017). Drag reductions were determined for both single
and multiphase experiments using Equation 1. The experiments were carried out for horizontal
flow, 2° inclination and also -2° and -5° inclinations (2° and 5° declinations). The results were
then compared.

3. Results and Discussion
3.1 Single Water Phase Drag Reduction
Figure 2 shows percentage drag reductions against polymer concentration at different Reynolds
number (NRE). It was observed that drag reduction increases as the polymer concentration is
increased. This may be as a result of the increased amount of polymer particles available to
interact in the system. These particles suppress eddies and further thicken the buffer layer
(Lumley, 1969). This phenomenon continues until a plateau point is reached. As observed at 400
ppm, further increase in the polymer concentration did not yield a corresponding increase in
drag reduction. Injection of 450 ppm and 500 ppm resulted in the same drag reduction as
observed at 400 ppm. This occurrence may be as a result of the turbulent structures of the flow
becoming saturated with DRA molecules (Edomwonyi-Otu, 2015) to the point where further
addition had very little effect on drag reduction; as the overall viscosity of the system is
increased (Hameed et al., 2014). It can thus be deduced that, for this system, 400 ppm of Aloe
Vera mucilage is the critical concentration.

Figure 2: Effect of polymer concentration on percentage drag reduction at various Reynolds
numbers.

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It can also be observed in Figure 2 that as Reynolds number increased, the drag reduction also
increased, until a threshold Reynolds number was reached at 62,949. After which (at Re=83,690)
drag reduction dropped significantly. This may be attributed to the increased Reynolds number
and subsequently, increased turbulence in the system; resulting in the polymer molecules
stretching further. As they stretch, they further absorb the energy within the system. This leads
to the suppression of turbulence and as a result, drag is reduced. The findings are in agreement
with results obtained from Yusuf et al., (2011) and Abubakar, (2016). Although they both used
synthetic polymers, they also observed a steady increase in drag reduction with increased
Reynolds number until a plateau point was reached. The maximum drag reduction observed for
this system was at 400 ppm, 450 ppm and 500 ppm.
However, beyond a Reynolds number of 62,949, it can be deduced from the increase in drag
(decrease in drag reduction) that the Aloe Vera mucilage undergoes mechanical degradation
due to the very high velocity within the system. As such, the DRA becomes much less effective
beyond this point. It has been reported that his mechanical degradation is one of the drawbacks
of natural polymers in drag reduction (Kamarulizan, 2012). For comparison, Abubakar, (2016)
used a synthetic copolymer of polyacrylamide and 2-Acrylamido-2-Methylpropane Sulfonic acid
and did not experience degradation of the DRA at Reynolds number as high as 120,000.
In view of these findings from the preliminary investigation, it is safe to suppose that further
increase in the concentration of the DRA beyond 400 ppm would not cause appreciable increase
in drag reduction. The single phase experiments also confirmed the use of Aloe Vera mucilage as
a drag reducing agent in single phase (water) flow, as established by (Abdulbari et al., 2011).
Different operating conditions were selected to improve data on the viability of the natural DRA
and it proved to be as effective as in their work.

3.2 Drag Reduction in Multiphase Flow
An optimum concentration of 400 ppm was used, as obtained from the single phase
experiments. Figure 3 represents the drag reduction obtained in the multiphase experiments.
The algebraic summation of the superficial velocity of water (Usw) and the superficial velocity of
oil (Uso) gives us the mixture velocity used in the experiments. It can be seen that drag
reduction is most effective in the pure water phase (α = 0). Subsequent addition of diesel
resulted in the percentage drag reduction reducing continuously until it is 0; in the pure diesel
phase (α = 1). Given that a water soluble DRA is used, it is expected that as the water Reynolds
number decreased, the drag reduction observed will decrease. Essentially, as the superficial
velocity of water (Usw) decreases, the water Reynolds number also reduces; thus reducing the
effectiveness of the drag reduction. As established in the single phase experiments and previous
works, drag reduction increases as Reynolds number increases and vice versa. This is in
agreement with the findings of Edomwonyi-Otu, (2015) and Abubakar, (2016). They noted that
addition of a water-soluble DRA in oil-water flow resulted in drag reduction being inversely
proportional to the oil input fraction. It can thus be deduced that drag reduction only takes
place in the water phase, since the aloe mucilage is insoluble in diesel oil and thus doesn’t
interact with it. A maximum drag reduction of 64% was therefore recorded at 0 oil fraction, 400
ppm and Um = 4.67 m/s.

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Abdallah, et al: Aloe Vera Mucilage as Drag Reducing Agent in Oil-Water Flow. AZOJETE, 15(2):248-258. ISSN 1596-
2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: uceclce@ucl.ac.uk 254

Figure 3: Effect of oil fractions on drag reduction at various mixture velocities (horizontal flow)

3.3 Effect of Inclination
Naturally, it is expected that the introduction of inclination will affect the total pressure drop of
the system as the gravitational pressure drop is affected either positively or negatively. Indeed,
Al-Sarkhi et al., (2006) established that an inclination of as little as 1.24o altered the effectiveness
of drag reduction. As observed by Abubakar, (2016) the new additional gravitational force
creates both normal and parallel pressure gradient components to the pipe axis. Figures 4 to 7
detail the effect of inclination on the system and the performance of the natural DRA used,
under these conditions. The optimum DRA concentration of 400ppm obtained in earlier
experiments was also used here.

Figure 4: Effect of oil fractions on drag reduction at various mixture velocities and 20 inclination
Figure 4 shows the effect of a 2o inclination on the drag reduction. It is observed that similarly to
the case of horizontal flow, drag reduction increases with increase in mixture velocity and
decrease in oil fraction. However, there is a slight increase of about 4% in drag reduction in the
2o inclined flow compared to the horizontal flow for α = 0, Um = 4.67 m/s and 400 ppm aloe
mucilage concentration. Consistently, other points on the 2o inclined flows showed slight
increase in drag reduction over the horizontal flows.
Lum et al., (2006) observed that the added gravitational flow component leads to increased
mixing between the phases. This in turn leads to dispersion of oil in the water phase thus
reducing the amount of oil in contact with the pipe walls (drag-inducing flow reduces),

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consequently reducing the total pressure drop of the system, and thereby enhancing the
effectiveness of drag reduction. These findings are in line with observations made by Abubakar,
(2016), who reported 3.33% higher drag reduction at 5o inclinations over horizontal flows in a
30.6 mm ID pipe. These results essentially indicate that inclination enhanced drag reduction for
the systems studied.

Figure 5: Effect of oil fractions on drag reduction at various mixture velocities and 20 declination

Figure 6: Effect of oil fractions on drag reduction at various mixture velocities and 50 declination
Figures 5 and 6 show the drag reductions measured at various input oil volume fraction and
mixture velocities, for 2° and 5° declinations, respectively. The highest drag reductions observed
for both 2° and 5° declinations were at zero oil fractions and were equal at were about 63.33%.
However, it is observed from figures 5 and 6 that the drag reductions at oil fraction of 0.25 for 2°
and 5° declinations at Umix = 4.67 m/s were 53.3% and 58.33%, respectively, within experimental
error (a slight 5% difference). These results show slight increase in drag reduction for the 5o over
the 2o case. This may be attributable to the greater gravitational flow component in the 5o case
as there is increased turbulence in this case that can lead to more mixing of the phases, thus
reducing the amount of oil in contact with the pipe walls (drag-inducing flow reduces),
consequently reducing the total pressure drop and thus increasing the drag reduction, of the
system.
A further comparison of the horizontal flow system (Figure 3) with the declination flows (Figures
5 & 6) showed mixed results. For instance, in the case of 400 ppm, Um=4.67 m/s, the horizontal,
2° and 5° declined flows show drag reductions of 53.8%, 53.3% and 58.33% respectively. This

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Abdallah, et al: Aloe Vera Mucilage as Drag Reducing Agent in Oil-Water Flow. AZOJETE, 15(2):248-258. ISSN 1596-
2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: uceclce@ucl.ac.uk 256

shows that a declination of 2° affected drag reduction similarly to horizontal flows and a further
declination to 5° yields slightly higher drag reduction than horizontal flows and also slightly
higher than 2° inclination (55.75%). This may occur due to the fact that as flow is aided by
gravitational forces, increased turbulence in the system can lead to uneven mixing. Which in turn
could lead to the DRA not uncoiling as effectively as in the horizontal set-up. Thus being less
effective when absorbing the energy of the flow; as such, hindering drag reduction. Thus
indicating that declination is not favorable for drag reduction. In addition, the angle of
inclination itself did not seem to significantly affect drag reduction.

Figure 7: Effect of angle of inclination on drag reduction
Figure 7 shows us that although inclination altered the effectiveness of drag reduction, it did so
to minimal degree, despite the introduction of the gravitational component to the flow system.
As the high velocity within the pipe negates a significant amount of the phenomenon observed.

4. Conclusion
From all the experiments carried out (testing the viability of Aloe Vera as DRA in oil-water flow)
and the results obtained, the following conclusions can be drawn:
A maximum drag reduction of 64% was achieved using a 12 mm ID pipe in single phase water
flow; agreeing with earlier work done by Abdulbari (2011) as similar conditions were used.
Drag reduction increased as Reynolds number increased until a Reynolds number of 62,949 was
reached. Indicating that the mucilage is a viable drag reducing agent only for Reynolds numbers
below 63,000
Multiphase flow experiments showed that the addition of the DRA only affected the water-
dominated flow regions. Indicating that drag reduction is only possible when the DRA is soluble
in the fluid being transported.
Drag reduction reduced as the oil fraction increased. Maximum drag reduction of 53.80% was
achieved at an oil input fraction of 25%
The effect of pipe inclination was significantly negated by the high velocity within the system.
Indicating that the DRA can viable for most pipe orientations.

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When used at Reynolds numbers below 63,000, Aloe Vera proved to be an effective DRA in oil-
water flow, thereby providing a biodegradable alternative to the synthetic polymers more
commonly used.
The synergistic effect of the mucilage should be studied, to further enhance its viability as a bio-
degradable alternative to synthetic polymers.
The findings obtained add substantial data to the study of drag reduction, as we strive towards
understanding the dynamics and most importantly, the mechanisms of drag reduction.

Acknowledgement
The Authors wish to thank all members of the Multiphase Flow and Separation Systems Research
Group of the Department of Chemical Engineering, Ahmadu Bello University, Zaria, for their
moral and technical support.

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