Accepted Manuscript

Title: Flow Characteristics of Surfactant StabilizedWater-in-Oil Emulsions

Author: M. Al-Yaari A. Al-Sarkhi I.A. Hussein F. Chang M.Abbad

PII: S0263-8762(13)00363-8DOI: http://dx.doi.org/doi:10.1016/j.cherd.2013.09.001Reference: CHERD 1367

To appear in:

Received date: 6-2-2013Revised date: 16-5-2013Accepted date: 6-9-2013

Please cite this article as: Al-Yaari, M., Al-Sarkhi, A., Hussein, I.A.,Chang, F., Abbad, M., Flow Characteristics of Surfactant Stabilized Water-in-Oil Emulsions, Chemical Engineering Research and Design (2013),http://dx.doi.org/10.1016/j.cherd.2013.09.001

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Flow Characteristics of Surfactant Stabilized Water-in-Oil Emulsions

M. Al-Yaaria, A. Al-Sarkhib, I. A. Husseina, F. Changc, M. Abbadc

aDepartment of Chemical Engineering, King Fahd University of Petroleum & Minerals, Saudi Arabia

bDepartment of Mechanical Engineering, King Fahd University of Petroleum & Minerals, Saudi Arabia

cSchlumberger Dhahran center for Carbonate Research, , Saudi Arabia

ABSTRACT

In this paper, an investigation was carried out to study the effect of water fraction and flow

conditions on the flow characteristics of surfactant stabilized water-in-oil emulsion.

Pressure drop measurements were conducted in 2.54-cm and 1.27-cm horizontal pipes. The

influence of water fraction and flow conditions on emulsion stability, type, conductivity,

droplet size distribution, viscosity and pressure drop were reported. The results showed a

significant increase in the emulsion stability, viscosity and pressure drop with increasing

water fraction up to 70%. In addition, shear thinning behavior was observed for the

emulsions especially at high water fractions. Furthermore, pressure drop measurements of

high concentrated emulsions showed pipe diameter dependency especially at high

Reynolds (Re) numbers. Moreover, drag reduction was observed with decreasing water

fraction. The viscosity of surfactant-stabilized water-in-oil emulsions were modeled with a

modified fluidity-additivity model.

Keywords: Water-in-Oil Emulsion; Shear Thinning; Pressure Drop;

b Corresponding author; Tel.: +966 3 8607725; Fax: +966 3 9602949; E-mail: alsarkhi@kfupm.edu.sa (A. Al-Sarkhi)

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INTRODUCTION

One of the common occurrences in the petroleum industry during transportation and

production is oil-water flow in pipes. Moreover, two-phase liquid-liquid flow is common

in the process and petrochemical industries. Although the accurate prediction of oil-water

flow is essential, oil-water flow in pipes has not been explored as much as gas-liquid flow.

The majority of studies reported in literature, have mainly focused on oil-water segregated

flow patterns (annular and stratified flow). The pipeline flow behavior of water-in-oil

and/or oil-in-water emulsions has received less attention.

Emulsion technology has been utilized in the acid treatment of reservoir rocks in the region

near well bore. Sometimes, the pore structure near the well bore is plugged either by

particulates from drilling process or by production precipitation deposits caused by

pressure or temperature changes. As a result, permeability is reduced as well as the well

productivity. To remove these unwanted deposits, acid stimulation is used. The carbonate

matrix acidizing process consists of injecting hydrochloric acid into the formation pore

space. The acid reacts with and dissolves portions of rock matrix and hence permeability is

increased. The effectiveness of the treatment depends on the penetration depth of the acid

into the formation.

Acid is consumed very quickly and it causes corrosion in the metal tubular goods.

Therefore, deep penetration of the acid as well as corrosion rate reduction is the target. One

method to achieve such retardation and to avoid corrosion is the use of the emulsified acid

where the hydrochloric acid is injected as a water-in-oil emulsion. To maintain

hydrochloric acid as the dispersed phase, it is necessary to use a composition that sits near

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the oil apex of the pseudo ternary diagram as reported by Hoefner and Fogler (1985) to

form stable emulsion.

Generally, water-in-oil or oil-in-water emulsions are unstable thermodynamically. As the

water/oil droplets are hydrophilic/ hydrophobic they tend to separate from the oil/ water

continuous phase. In order to form a stable emulsion, a surfactant (emulsifier) must be used

to reduce the interfacial tension and promote the formation of smaller droplets. High

pressure drop, caused by friction losses, can be a problem while pumping emulsified acid.

As a result, emulsified acid is pumped at low flowrates and thus limited job efficiency is

achieved. Consequently, methods of pressure drop reduction are highly desired.

Laminar and turbulent flow behaviors of unstable oil-in-water and water-in-oil emulsions

in pipes have received a considerable attention (Baron et al. (1953), Cengel et al. (1962),

Pal (1987), Pal (1993), Angeli and Hewitt (1998), Masalova et al. (2003), Pal (2007), Al-

Yaari et al. (2009) and Omer and Pal (2010)). The emulsion effective viscosities were

calculated form single phase Hagen-Poiseuille equation and Blasius equation for laminar

and turbulent flow, respectively. It was reported that since emulsion effective viscosity

calculated for turbulent flow is lower than that for laminar flow or since the measured

turbulent pressure drop is lower than that calculated from Blasius equation, drag reduction

was claimed (Cengel et al. (1962), Pal (1987), Pal (1993), and Omer and Pal (2010)). In

addition, it was reported that such drag reduction increases with: the increase in the volume

fraction of the dispersed phase (Pal (1987) and Pal (1993)); the decrease in pipe diameter

(Pal (1993) and Masalova et al. (2003)) and the decrease in the viscosity of oil continuum.

(Omer and Pal (2010)). Moreover, drag reduction is a function of emulsion type (Pal 1993)

and pipe material (Angeli and Hewitt (1998)). Droplets stretching and elongation, in

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turbulent regime, is proposed as a mechanism of the reported drag reduction of studied

unstable emulsions (Pal (2007)). Furthermore, phase inversion of unstable emulsions was

also reported (Pal (1993) and Al-Yaari et al. (2009)).

However, pipeline flow behaviors of stable oil-in-water and water-in-oil emulsions have

received less attention. While drag reduction was reported for surfactant stabilized oil-in-

water emulsions (Rose and Marsden (1970) and Zakin et al. (1979)), little or no drag

reduction was addressed for surfactant stabilized water-in-oil emulsions (Pal (1993) and

Omer and Pal (2010)). In addition, with increased dispersed phase volume fraction, phase

inversion and increased emulsion effective viscosities, calculated from the single phase

equations, were reported (Pal (1993) and Omer and Pal (2010)).

This paper aims at studying the flow characteristics of surfactant stabilized water-in-oil

emulsions. The influence of water (dispersed phase) fraction on emulsion stability, droplet

size, viscosity and pressure drop is investigated. Also, it aims to examine a possible friction

reduction through the control of water fraction. In addition, stable water-in-oil emulsions

dependency on pipe diameter are studied.

EXPERIMENTAL SETUP & PROCEDURE

Surfactant stabilized water-in-oil emulsions were prepared using brine (with 50 kppm

NaCl) as the aqueous phase and a type of kerosene, known as SAFRA D60 produced in

Saudi Arabia, as the oil phase.. Some physical properties of the oil are presented in Table

1. The emulsifying agent is ARMAC T from Akzo Nobel (Tallowalkylamine acetates),

was used as the surfactant (emulsifier) and its physical properties are tabulated in Table 2.

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Schematic layout of the flow loop is shown in Figure 1. The flow loop consists of two

small tanks (1 and 2), made from PVC, with a volume of 70 liters each. Two centrifugal

pumps (3 and 4) are used for low and high pumping rates. Test sections are two horizontal

pipes with inside diameter of 2.54-cm and 1.27-cm made from acrylic resin to allow visual

observation. Flowrate is measured by two OMEGA magnetic flowmeters (5 and 6). The

total length of the flowloop test sections is 11 m. Emulsion pressure drop is measured by

two differential pressure transducers (7 and 8), made by ROSEMOUNT Company. The

first pressure tap, of each, is located at 8 m from the entrance to be sure that the flow is

fully developed. The two pressure taps are 1 m apart from each other. In addition, the

flowloop contains a conductivity measurement cell, which is used to detect the emulsion

type and to measure emulsion conductivity while flowing in the 2.54-cm piping system.

The conductivity measurements as well as pressure drop measurements are monitored by

PC through a data acquisition system. Furthermore, emulsion temperature was maintained

at 25 oC by the designed cooling system, consisting of a chiller (9), brass coiled tubings

and a submersible pump, as illustrated in Figure 1.

Information and accuracies of the used flowmeters and differential pressure transmitters’

are presented in Table 3. All uncertainties were calculated within the 95 % confidence

level using a method described by Dieck (2007). The uncertainty values summarized in

Table 3 represent the combined uncertainties of random and systematic uncertainties.

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Emulsion Preparation

36 liters of surfactant stabilized water-in-oil emulsions were made by adding the required

volume % of brine at 1 L/min to the emulsified oil (oil with 0.6 volume % emulsifier)

while mixing at 8000 RPM (for 30 minutes) by using high power homogenizer (Ultra

Turrax T 50 basic, WERKE IKA, Germany). Emulsion quality was tested by dilution and

conductivity measurements tests. Emulsions were then transferred to one of the flowloop

tanks. This procedure was followed to prepare all emulsions with different brine volume

fraction.

Stability Test

Bottle test was used to achieve stability tests for all formed emulsions by monitoring

percentage of separated oil and/or separated water layers with time. Such test can give an

indication about emulsion quality. In other words, it can tell qualitatively about the average

size of the dispersed phase (brine) droplets. As a rule of thumb, the smaller the droplets,

the more stable the emulsion is if other conditions are same.

Emulsion type

Dilution test was used to identify the emulsion continuous (external) phase. In this test, a

droplet of the formed emulsion was injected in an oil or water sample. If the injected

droplet disperses, the emulsion continuous (external) phase is the same as the fluid used for

the test. For example, water-in-oil emulsion droplets disperse in oil and oil-in-water

emulsions disperse in water. Also, emulsion type was detected by measuring its

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conductivity. This test is based on the fact that brine solution is conductive and oil is

nonconductive and emulsion continuous phase is dominating emulsion conductivity.

Rheological Test

All rheological measurements were conducted using Rheologica StressTech rheometer.

The rheometer has a torque range from 3.0x10-8 to 2.0x10-1 N∙m with a torque resolution of

1.0x10-10 N∙m. The bob/cup set, where bob is the rotating part, was used to conduct steady

shear rate sweep tests. The tested emulsion volume is 15.9 cm3.

Once water-in-oil emulsions have been produced, steady shear rate sweep tests were

conducted to produce emulsion viscosity curves at different water fractions. In this test,

15.9 cm3 of the emulsion sample, containing specific water composition, was sheared

gradually with increasing the bob rotating speed till a level where the emulsion sample

started spelling out of the cup. The shear rate at this point (upper shear rate), for all the

tested emulsions, was ≥ 1000 s-1. The upper shear rate increases as emulsion viscosity

increases.

RESULTS AND DISCUSSION

Emulsion stability

To investigate the effect of water fraction on emulsion stability, emulsions with different

water to oil volume % (10/90 (a), 40/60 (b), 50/50 (c), 60/40 (d) and 70/30 (e)) were used.

Brine with 5 wt% NaCl (50 kppm) was used as an aqueous phase. This concentration was

used to have water-in-oil emulsion over the whole range of water volume fraction from 10

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to 70 % and to eliminate the inversion to oil-in-water emulsion. As an example if 10 kppm

NaCl is used for the 70/30 water to oil volume fraction case, then oil-in-water emulsion

will exist. After preparing such emulsions, stability tests were carried out using bottle test,

by monitoring phase separation with time. These results are presented in Figures 2 and 3.

Although the emulsion preparation procedure is the same (including the emulsification

time and intensity and the brine adding rate), an increase in the volume fraction of the

dispersed phase (water) resulted in more concentrated emulsion and the chance for the

dispersed phase droplets to sediment was lower and the separation occurred only from the

oil side.

As shown in these figures, increasing water fraction resulted in more stable emulsion. As

water fraction increased, the dispersed phase droplets size became smaller (see Figure 4).

This is obvious because when diluted system is mixed, the probability of the dispersed

phase droplets to break is lower than that for concentrated systems. Thus, stable water-in-

oil emulsion with 0.7 volume fraction of water was the most stable one compared with the

other emulsions covered in this study.

Emulsion type and conductivity

Emulsion type and conductivity tests were conducted by dilution tests and conductivity

measurements tests, respectively. Emulsion conductivity test was conducted statically,

after preparing the emulsion using a conductivity meter. All the tested emulsions were

water-in-oil with a conductivity of 0 μS/cm (static test), which was confirmed by dilution

test.

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Emulsion droplets size distribution

Some microscopic photos were taken for all tested emulsions. Since all emulsions were

milky, careful use of cover slips were mandatory to get micrographs. These photos are

shown in Figure 4.

As shown in this figure, increasing the water (dispersed phase) fraction resulted in tight

emulsion with smaller droplet size distribution of the dispersed phase which enhances

emulsion stability.

Emulsion Rheology

Viscosity curves for all surfactant stabilized water-in-oil emulsions were produced using a

Bob and Cup viscometer. As shown in Figure 5, almost all emulsions showed a shear

thinning behavior. Shear rate dependency of the viscosity increases as brine (dispersed

phase) volume fraction increases. Steady shear rate viscosities were used to calculate

emulsion Reynolds numbers (Re) at different shear rates (flowrates).

Power-law or Ostwald-de Waele model represents the fluid viscosity as a function of shear

rate ( as shown in equation (1) where k and n are the consistency and the power-law index,

respectively. It can be used for shear thinning fluids for the shear rate range within which viscosity

decreases as shear rate increases. Water-in-oil emulsions behaved as shear thinning fluids when

water volume fraction was ≥ 0.4 (see Table 4).

��= ����̇��−1 (1)

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The true wall shear rate and the behavior index (n) were calculated using equations (2) and

(3), respectively (Wilkes, 2010). However, and are related to the power-law

constants as shown in equations (4) and (5), respectively (Wilkes, 2010). In addition, zero-

shear rate viscosity ( o ) as well as infinite-shear rate viscosity ( ) of all emulsions were

calculated from data fittings using Cross model (R2 ≥ 0.99), expressed by equation (6).

Behavior index (n, n’), consistency index (k, k’), ηo and η∞ shear rate viscosities are

reported in Table 4.

��̇�� = 4 ������334 + 14 ��(ln��)��(ln����) (2)

where w = True wall shear rate

Q = Volumetric flowrate

R= Pipe radius

w = Wall shear stress

The term in brackets in equation (2) is the Robinowitsch correction for non-Newtonian

fluids.

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��(ln��)��(ln����) = 1 �� (3)

��– ��∞����− ��∞ = 11 + (�� )

�� (6)

where = Emulsion viscosity

ηo = Emulsion zero shear rate viscosity

η∞= Emulsion infinite shear rate viscosity

= Shear rate

λ, m = constants

By fitting data presented in Figure 6, ηo and η∞ for stable water-in-oil emulsion can be

related to water fraction (xw) as shown in equations (7) and (8), respectivelly.

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ηo = ηoil *e5.8344 xw (7)

��∞ = ��������∗ ��4.3504 ���� (8)

where ηo = Emulsion zero shear rate viscosity

η∞ = Emulsion infinite shear rate viscosity

ηoil = Oil viscosity

xw = Water fraction

The mixture viscosity (η) of immiscible liquids can be expressed by the Fluidity Additivity

equation (Equation (9)) as reported by Bingham (1922). Lin (1979) introduced slip factor

(λ) to account for slippage effect in polymer liquids (Equation (10)). However, those

equations did not account for the presence of emulsifier and hence underestimate water-in-

oil emulsion viscosities at different water fraction. Therefore, a viscosity enhancement

factor (β) is introduced (Equation (11)). This factor, expressed by equation (12), is a strong

function of water fraction and at low shear rates (flowrates) it depends on shear rate as

well. Figure 7 shows a comparison between the fluidity additivity model ( Equation (9))

and the proposed model (Equation (11) and (12)) to predict stable water-in-oil emulsion

viscosities. Noting that the Cross model (equation (6)) used only to calculate the emulsion

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zero and infinite shear rate viscosities. The proposed model fits the experimental data very

well.

1��= ��������+ �������� (9)

where η = Emulsion or mixture viscosity

xw = Water fraction

x0 = Oil fractio

ηw =Water viscosity

ηo = Oil viscosity

1��= [1 + ��(��������)0.5] ��������+ �������� (10)

1��= 1− ��(��������)0.5 ��������+ �������� (11)

��= 1.2381 ��0.7721 ���� (12)The majority of the proposed models to predict emulsion viscosities are for low capillary

numbers (Nca 0), where the emulsion droplets are almost spherical and under creeping

flow conditions (Re 0) (Hatschek (1911), Richardson (1933), Broughton and Squires

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(1938), Eilers (1941) and Pal and Rhodes (1989)). Therefore, their models are not

function of shear rate.

������= ��̇�������� (13)

wherec = Viscosity of the continuous phase

Rd= Droplet radius

σ= Interfacial Tension

However, our proposed model is adding the shear rate effect. In addition, other proposed

models such as that proposed by Pal (2003); although it is not for zero capillary No., it’s

more complicated and additional information such as interfacial tension, droplet radius,

…etc are required to use it.

Emulsion Pressure Drop

Pressure drop of all prepared surfactant stabilized water-in-oil emulsions were measured at

different flowrates in both 2.54-cm and 1.27-cm pipes. All measurements were conducted

at steady state conditions. Emulsion temperature was maintained at 25 oC. Based on the

pipe flow shear rate (Equation (1)), emulsion viscosity were extracted from rheological

measurements and used to calculate Reynolds number for emulsion flow. Reynolds

number (Re) and friction factor (f) were defined as shown in equations (13) and (14),

respectively.

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����= �������� (14)

where ρ= Emulsion density at 25 oC

u = Emulsion average velocity

D= Pipe diameter

= Emulsion viscosity extracted from the steady shear rate sweep test data at the

flow corresponding shear calculated by equation (1) at 25 oC

L

P

= Fully developed pressure gradient

Pressure drop measurements results for emulsions in the 2.54-cm pipe are illustrated in

Figure 8. However, pressure drop results for emulsions in the 1.27-cm pipe are illustrated

in Figure 9. As shown in these figures, as water (dispersed phase) fraction increased

frictional pressure drop, due to emulsion flow in both pipes, increased significantly

especially in laminar regime. This is could be due to emulsion crowding at high dispersed

phase volume fraction. In addition, surfactant stabilized dispersed phase droplets have

strong interface. Therefore, emulsion viscosity as well as stability will be higher with

increasing water fraction.

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Emulsion Pressure Drop Reduction

Understanding surfactant stabilized water-in-oil emulsions will help to achieve one of the

important practical goals, which is pressure drop reduction of such stable emulsions. Based

on the results presented in this paper, pressure drop reduction of surfactant stabilized

water-in-oil emulsions can be achieved by controlling the water fraction and pipe diameter.

Firstly, pressure drop reduction of stable water-in-oil emulsions can be achieved by

decreasing the water fraction (at least for the studied range of Re). For example, for the

acidizing purpose, emulsified acid contains 70 volume % water. Therefore, if water

fraction is reduced to 60 volume % water, pressure drop could be reduced by (78% to 48%)

in 2.54-cm pipe and by (63% to 41%) in 1.27-cm pipe for Re range of (100 to 1000).

Figures 10 and 11 present the percentage of emulsion pressure drop reduction, if emulsion

water fraction was reduced from 0.7 to lesser values, in 2.54-cm and 1.27-cm pipes,

respectively. The pressure drop reduction relative to the 70% case was defined as follows:

brine

brinexbrine

P

PP

%70

%%70Reduction Dropessur Pr

(16)

where

ΔP70% brine = Pressure drop of emulsion containing 70 volume % water

ΔPx% brine = Pressure drop of emulsion containing x volume % water

In the carbonate acidizing process, higher acid volume fraction is preferable to do the job.

Therefore, emulsified acid with only 10% volume fraction of acid cannot be used although

the pressure drop is very low.

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Secondly, as shown in Figures 12-14, surfactant stabilized water-in-oil emulsions showed

emulsion friction factor reduction with decreasing pipe diameter and this effect increased

with increasing water fraction for low Re. This could be attributed to the viscoelastic

properties of high concentrated emulsions.

CONCLUSIONS

Emulsion flow characteristics of surfactant stabilized water-in-oil emulsions at different

water fractions and pipe diameters have been studied. Such emulsion features include:

stability, type, conductivity, viscosity and pressure drop. Stable water-in-oil emulsion with

70% volume of brine was the most stable one compared with the other tested emulsions

and showed the highest pressure drop at the same flowrate. As the dispersed phase (water)

fraction decreased, emulsion stability, viscosity as well as pressure drop decreased for all

emulsions reported in this paper at different pipe diameters. Therefore, surfactant stabilized

water-in-oil emulsions pressure drop can be reduced by reducing brine (dispersed phase)

volume fraction. In addition, surfactant stabilized water-in-oil emulsions friction factor

can be reduced by pumping fluids in small pipe diameters due to the shear thinning effect

of the high concentrated stable emulsions. It is highly recommended to investigate such

effects at high Reynolds number. Furthermore, surfactant-stabilized water-in-oil emulsions

viscosity was modeled with a modified fluidity-additivity model as shown in equations 10

and 11.

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ACKNOWLEDGMENTS

The authors would like to acknowledge the support provided by King Abdulaziz City for

Science and Technology (KACST) for funding this work through project No. 09-OIL

788-04. The technical support provided by Schlumberger Dhahran center for Carbonate

Research (SDCR), Saudi Arabia, is highly appreciated.

REFERENCES

Al-Yaari, M., Abu-Sharkh, B., Soleimani, A., Al-Mubayeidh, U., Al-Sarkhi, A., 2009,

Effect of drag reducing polymers on oil-water flow in a horizontal pipe, Int. J. Multiphase

Flow, 35, 516–524.

Angeli, P. and Hewitt, G., 1998, Pressure gradient in horizontal liquid-liquid flows, Int. J.

Multiphase Flow, 24, 1183-1203.

Baron, T., Sterling, C. and Schueler A., 1953, Viscosity of suspensions-review and

application to two-phase flow, Proc. Midwestern Conf. on Fluid Mechanics, 103, Univ. of

Minnesota Institute of Technology, Minneapolis.

Bingham, E. C., 1922, Fluidity and elasticity, McGraw-Hill, New York.

Broughton, J., and Squires, L., 1938, The viscosity of oil-water emulsions, J. Phys. Chem.,

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Cengel, J., Faruqui, J., Finnigan, W., and Knudsen J., 1962, Laminar and turbulent flow of

unstable liquid-liquid emulsions, AIChE J, 8(3), 335.

Dieck, R., 2007, Measurement uncertainty methods and applications, 4th Edition, the

Instrumentation, Systems and Automation Society (ISA), USA.

Eilers. H., 1941, The viscosity of very viscous emulsion materials as a function of

concentrations, 97, 313.

Hatschek, E., 1911, Viscosity of the dispersion, Kolloid-Z, 8, 34.

Hoefner, M. and Fogler, H., 1985, Effective matrix acidizing in carbonates using

microemulsions, Chem. Eng. Prog., 81(5), 40-44.

Lin, C., 1979, A mathematical model for viscosity in capillary extrusion of two-component

polyblends, Polymer J. (Tokyo), 11, 185-192.

Masalova, I., Malkin A., Slatter, P., and Wilson, K., 2003, The Rheological

characterization and pipeline flow of high concentration water-in-oil emulsions, J. Non-

Newtonian Fluid Mech., 112, 101-114.

Omer, A. and Pal, R., 2010, Pipeline Flow behavior of water-in-oil emulsions with and

without a polymeric additive, J. Chem. Eng. Tech., 33(6), 983-992.

Pal, R., 1987, Emulsions: Pipeline flow behavior, viscosity equations and flow

measurement, PhD Thesis, University of Waterloo, Ontario.

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Pal, R., 1993, Pipeline flow of unstable and surfactant stabilized emulsions, AIChE J, 39

(11), 1754-1764.

Pal, R., 2003,Viscous behavior of concentrated emulsions of two immiscible newtonian

fluids with interfacial tension, J. Colloid Interf. Sci., 263, 296-305.

Pal, R., 2007, Mechanism of turbulent drag reduction in emulsions and bubby suspensions,

Ind. Eng. Chem. Res., 46 (2), 618-622.

Pal, R., and Rhodes, E., 1989, Viscosity/concentration relationships for emulsions, Journal

of Rheology, 33 (7), 1021-1045.

Richardson, E., 1933, Viscosity of emulsions, Kolloid-Z, 65, 32.

Rose, S., and Marsden, J., 1970, The Flow of north slope crude oil and its emulsions at low

temperatures, SPE 2996, SPE 45th Annual Fall Meeting and Exhibition, Houston.

Wilkes, J., 2010, Fluid mechanics for chemical engineers, 5th edition, Prentice Hall, USA.

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Figures captions

Figure 1: A Schematic layout of the flowloop

Figure 2: Effect of water volume fraction on water-in-oil emulsion stability

Figure 3: Water-in-oil emulsion stability (after 2 hours) at different water volume fractions; a:

0.1, b: 0.4, c: 0.5, d: 0.6 and e: 0.7

Figure 4: Water-in-oil emulsion droplets size and distribution at different water volume

fractions; a: 0.1, b: 0.4, c: 0.5, d: 0.6 and e: 0.7

Figure 5: Effect of water fraction on water-in-oil emulsion viscosity

Figure 6: Effect of water fraction on emulsions zero and infinite shear rate viscosities at 25 oC

Figure 7: Comparison of experimental data of stable water-in-oil emulsion viscosities with

predictions using Fluidity Additivity and the proposed models

Figure 8: Effect of Reynolds number on water-in-oil emulsion pressure drop in 2.54-cm pipe at

different water fractions

Figure 9: Effect of Reynolds number on water-in-oil emulsion pressure drop in 1.27-cm pipe at

different water fractions

Figure 10: Emulsion pressure drop reduction in 2.54-cm pipe by changing water volume fraction

from 0.7 to lesser values

Figure 11: Emulsion pressure drop reduction in 1.27-cm pipe by changing water volume fraction

from 0.7 to lesser values

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Figure 12: Friction factor of stabilized water-in-oil emulsion with 0.1 water volume fraction

Figure 13: Friction factor of stabilized water-in-oil emulsion with 0.5 water volume fraction

Figure 14: Friction factor of stabilized water-in-oil emulsion with 0.7 water volume fraction

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Tables captions

Table 1: Properties of the oil phase

Table 2: Properties of the emulsifying agent

Table 3: Instruments information and accuracies

Table 4: Some rheological parameters of water-in-oil emulsions at 25 oC

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.

Figure 15: A Schematic layout of the flowloop

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Figure 16: Effect of water volume fraction on water-in-oil emulsion stability

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Figure 17: Water-in-oil emulsion stability (after 2 hours) at different water volume fractions;

a: 0.1, b: 0.4, c: 0.5, d: 0.6 and e: 0.7

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Figure 18: Water-in-oil emulsion droplets size and distribution at different water volume

fractions; a: 0.1, b: 0.4, c: 0.5, d: 0.6 and e: 0.7

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Figure 19: Effect of water fraction on water-in-oil emulsion viscosity

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Figure 20: Effect of water fraction on emulsions zero and infinite shear rate viscosities at 25 oC

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Figure 21: Comparison of experimental data of stable water-in-oil emulsion viscosities with predictions using Fluidity Additivity and the proposed models

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Figure 8: Effect of Reynolds number on water-in-oil emulsion pressure drop in 2.54-cm pipe at

different water fractions

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Figure 9: Effect of Reynolds number on water-in-oil emulsion pressure drop in 1.27-cm pipe at

different water fractions

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Figure 22: Emulsion pressure drop reduction in 2.54-cm pipe by changing water volume fraction

from 0.7 to lesser values

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Figure 23: Emulsion pressure drop reduction in 1.27-cm pipe by changing water volume fraction from 0.7 to lesser values

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Figure 24: Friction factor of stabilized water-in-oil emulsion with 0.1 water

volume fraction

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Figure 25: Friction factor of stabilized water-in-oil emulsion with 0.5 water volume fraction

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Figure 26: Friction factor of stabilized water-in-oil emulsion with 0.7 water volume fraction

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Table 4: Properties of the oil phase

Product Name SAFRA D60

Flash Point 67 C

Density 780 kg/m3

Viscosity 1.57 cp @ 25C

Interfacial Tension Oil-Water 0.017 N/m @ 20C

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Table 5: Properties of the emulsifying agent

Commercial Name ARMAC T

Common Name Tallowalkylamine acetates

Appearance @ 25 oC Solid

Hydropile- Lipophile Balance (HLB) 6.8

Table 6: Instruments information and accuracies

Parameter Test Section Instrument Supplier Range Uncertainty1.27-cm pipe 0.001%

Flow rate2.54-cm pipe

Magnetic Flowmeter

OMEGA0 - 30

gal/min 0.584%1.27-cm pipe 0 - 1.8 psi 0.391%Pressure

Drop 2.54-cm pipe

Smart Rosemount Pressure

TransmitterEmerson

0 - 0.8 psi 0.732%

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Table 7: Some rheological parameters of water-in-oil emulsions at 25 oC

Behavior Index Consistency IndexZero-Shear Rate

Viscosity, Pa.s

Infinite-Shear Rate Viscosity,

Pa.sWater

Fraction(xw)

n n' k k' ηo η∞

0.7 0.614 0.614 0.4502 0.27052 0.09515 0.0336

0.6 0.586 0.586 0.3302 0.19415 0.05642 0.022

0.5 0.346 0.346 0.703 0.38561 0.02246 0.0118

0.4 0.403 0.403 0.4437 0.24216 0.019071 0.0101

0.1 N/A N/A N/A N/A 0.00281 0.00243

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Highlights

Characteristics of surfactant stabilized water-in-oil emulsions flow are investigated.

Significant increase in the emulsion stability, viscosity and pressure drop with increasing

water fraction up to 70%.

Shear thinning behavior was observed for the emulsions especially at high water fractions.

The rheology of surfactant-stabilized water-in-oil emulsions were modeled with a modified

fluidity-additivity model.

Pipe diameter effect on pressure drop of surfactant stabilized water-in-oil emulsions is

identified

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Figure 1: Friction factor of stabilized water-in-oil emulsion with 0.5 water volume fraction

0.01

0.1

1

100 1000 10000

Fri

ctio

n F

acto

r,ƒ

Reynolds Number, Re

ID= 2.54 cm

ID= 1.27 cm

Hagen Poissuille Eq.

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Figure 2: Friction factor of stabilized water-in-oil emulsion with 0.7 water volume fraction

0.01

0.1

1

100 1000

Fri

ctio

n F

acto

r,ƒ

Reynolds Number, Re

ID= 2.54 cm

ID= 1.27cm

Hagen Poiseuille Eq.