1 Copyright © 2014 by ASME

EFFECT OF VISCOSITY ON THE PRESSURE GRADIENT IN 4-INCH PIPE

M. Mudasar Imamb mudasarimam@kfupm.edu.sa

Mehaboob Bashaa nbbasha@kfupm.edu.sa

S. M. Shaahida mshaahid@kfupm.edu.sa

Aftab Ahmada aftab@kfupm.edu.sa

Luai M. Al-Hadhramia

luaimalh@kfupm.edu.sa

a Centre for Engineering Research- Research Institute

b Department of Mechanical Engineering

King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia

ABSTRACT

The pressure drop of liquids of different viscosities in

multiphase flow is still a subject of research. This paper

presents pressure drop measurements of water and oil single

phase flow in horizontal and inclined 4 inch diameter stainless

steel pipe at different flow rates. Potable water and Exxol D80

oil were used in the study. Experiments were carried out for

different inclination angles including; 0°, 15°, 30° (upward and

downward flows). Inlet liquid velocities were varied from 0.4

to 1.2 m/s and reference pressure was set at 1 bar. Water and

Oil viscosities are 0.798 Pa.s and 1.56 Pa.s at 30°C,

respectively.

Pressure drop has been found to increase with increase in liquid

velocity. Pressure drop has been observed to increase

asymptotically with pipe inclination. Upward flows are

associated with high pressure drop as compared to downward

flows. The pressure drop of water is greater than that of oil for

all inclinations. This difference can be attributed to the

difference in fluid viscosities and densities. Measured pressure

drops were compared with existing empirical relations and

good agreement was noticed.

Keywords: Multiphase flow-loop, Pressure drop, inclined

pipe, Viscosity effect.

INTRODUCTION

The pressure drop of liquids of different viscosities in

multiphase flow is still an active research area. This is partly

because fluids with different properties exhibit different flow

behaviors in different pipe configurations under different

operating conditions. Even a single phase flow with different

viscosities can impact pressure drop appreciably.

Fan and Hanratty [1] proposed correlation to predict the

pressure drop across a pipeline. In their model hydraulic jump

is considered to be due to slug. They concluded that pressure

drop change could be positive or negative depending on growth

of slug. Greskovich and Shrier [2] extended the work of

Hubbard and Dukler to predict the pressure gradient. They used

1.5 inch diameter pipe to measure the pressure gradient. Then

they compared their predicted values of pressure gradient to the

experimental pressure gradient taken from various systems and

pipes.

A new model was introduced by Gopal [3] to predict the

pressure gradient and liquid holdup independent of pipe

geometry and fluid properties. They used the iterative

procedure to calculate these values. Barnea and Brauner [4]

investigated liquid holdup of two phase flow in both horizontal

and vertical pipes.

Andritsos and Hanratty [5] considered the influence of

interfacial stress effect in gas-liquid two phase flows. These

stresses were calculated by measuring the liquid height and

pressure gradient for a horizontal pipe when flow is fully

developed. A computational approach was developed by

Vlachos and Karabelas [6] to predict liquid holdup and wall

shear stress. They compared their predicted values with

experimental ones and results showed good agreement.

Maley [7] investigated the void fraction distribution in a slug

with various gases and liquids. They used large diameters pip to

Proceedings of the ASME 2014 International Mechanical Engineering Congress and Exposition IMECE2014

November 14-20, 2014, Montreal, Quebec, Canada

IMECE2014-37918

2 Copyright © 2014 by ASME

conduct experiments. This model was used to predict the liquid

holdup. An equation was introduced by Hubbard and Dukler [8]

to calculate the total pressure gradient in one and two phase

system. They assumed that when the two phases are

homogenously mixed and there is no slip between them then

the frictional pressure gradient could be calculated by an

equation similar to ones in single phase flow. The effect of

inclination on slug characteristics was studied by

Mantripragada [9]. In this work it was concluded that at low

superficial liquid velocities the gravity has dominant effect than

at high superficial liquid velocities. It was further concluded

that slug velocity was found independent of pipe inclination.

The objective of the present study was to measure pressure

drop of water and oil single phase flow in horizontal and

inclined 4 inch diameter stainless steel pipe at different flow

conditions. Two fluids (water & oil) with different viscosities

and densities were used. Water and Oil viscosities are 0.798

Pa.s and 1.56 Pa.s at 30°C, respectively. Experiments were

conducted for different inclination angles including; 0°, 15°,

30° (upward and downward flows). Inlet velocities were varied

from 0.4 to 1.2 m/s and reference pressure was set at 1bar.

EXPERIMENTAL SETUP

The water and oil single phase experiments were

conducted at recently established multi-phase laboratory at

King Fahd University of Petroleum and Mineral (KFUPM),

Dhahran, Saudi Arabia. The multi-phase flow loop is equipped

with a screw type compressor (AC), two compressed air tanks

(CAT), five centrifugal variable speed pumps(3 for pumping

water WP and 2 for pumping oil, OP), two-pass 4 inch stainless

loop (28 m length), a horizontal separator tank (WOST), two

level indicators for oil and water each. The loop is constructed

on moveable platform (inclination can be varied from 0 deg -

60 deg), which toggles on flexible pipe connection (FC). The

loop can be positioned at any given angle using over-head jack.

The layout of the flow loop is presented in Fig 1. The loop is

instrumented with air flow meter (AFM), two ultra-sonic oil

flow meter (OFM), three magnetic water flow meters (WFM),

air pressure regulator (PR), line pressure transmitter (LPT),

one upward flow differential pressure transmitter (DPT1), one

downward flow differential pressure transmitter (DPT1),

turbine flow meter (TFM). More details of the loop components

and instruments are given in table 1.

WGV WOST

WP1

WP2

WP3

OP1

OP2

OGV

WFM

OFM

Top Veiw

TFM

FC

FC

AFM

AGV

AC

CAT

Upstream

Downstream RGV

FC

Upstream

30°

15°

FC

Downstream

-30°

-15°

Return

Side View

DPT2

DPT1

LPT

PR

FIGURE 1 SCHEMATIC LAYOUT OF THE MULTIPHASE

FLOW LOOP.

TABLE 1 DETAILS OF EQUIPMENT

items Manufactur

er

Model Capacity/R

ange

Accurac

y/Error

Screw type

compressor

JAGUAR EAS20 8.5 bar -

Two

compressed

air tanks

1-

JAGUAR

2-

JAGUAR

1-GB150-

98

2-60034-1

1-1.43 mpa

2-0.8 mpa

-

Five pump

(three

water, two

oil)

NEWAR

FLOW

SERVE

50-

32CPX200

35 m3/hr -

Air flow

meter

OMEGA FMA-

1613A

4-60

ACFM

±1.0 %

Two

ultrasonic

flow meter

Spire

metering

technology

EF10 ±10 m/s ±1.0 %

Three

electromag

netic flow

meter

Spire

metering

technology

MAG888 ≤12m/s ±0.5%

Line

pressure

gauge

ROSEMO

UNT

AOB-20 0-7 bar ±0.25%

DP1

upward

ROSEMO

UNT

300S2EAE

5M9

0-70 inches

of water

column

±0.1%

DP2

downward

ROSEMO

UNT

300S2EAE

5M9

0-10 inches

of water

column

±0.1%

3 Copyright © 2014 by ASME

Oil flow

FIGURE 2 FLOW LOOP INLETS.

FIGURE 3 FRICTION FACTORS FOR SINGLE PHASE OIL

AND WATER

EXPERIMENTAL PROCEDURE

Experiments were conducted for water and oil single

phase to validate the measurements of the loop against

available models, and to calibrate instruments (pressure

transmitter and flow meters) of the loop. In this respect, water

is pumped in the loop using induction motors powered pumps.

Required volume flow rate was attained by varying speed of

induction motor through variable speed drives. Magnetic flow

meters installed on pumps were used for measuring the

cumulative flow rate. Return gate valve (RGV, figure1) of the

loop is throttled to set the required outlet pressure (eg. 1 bar or

2 bars). For given flow rate, experiments were conducted

pressure drop measurements were made on either side of the

loop. Differential pressure were recorded when the flow

reached steady state. CR 1000 was used to log experimental

data. Similar procedure is followed for oil flow experiments.

Figure 2 shows flow loop inlets.

Pressure drop data was used to calculate friction factor

using Eq. (1) and compared with Eq. (2) and Eq. (3).

f =∆P

L

2D

ρv2 (1)

∆P Pressure drop (Pa). L distance between the two pressure taps (m).

D inner diameter of the pipe (m).

ρ fluid density (Kg m3)⁄ .

v average velocity of the fluid (m/s).

ε pipe roughness (m).

Re Reynolds number

𝑓 = 0.079 𝑅𝑒−1/4 (2)

The turbulent friction factor can also be determined using other

correlations, such as the Zigrang & Sylvester 1985 correlation

defined in eq. (2) above.

1

√f= −2log [

ε D⁄

3.7−

5.02

Relog [(

ε D⁄

3.7) +

13

Re]] (3)

Then this friction factor was compared with the friction factors

calculated by using Blasius correlation and Zigrang & Sylvester

correlations as shown in the figure 3. The result showed a close

agreement particularly with the Blasius friction factor.

Figure 4 shows the pressure drop of single phase water and oil

for horizontal flows against liquid velocity. As known, pressure

gradient drop increases with increase in velocity. Experimental

data is found to be in good agreement with established

theoretical relation (Eq. 1). Figure 3 shows the comparison of

friction factor from present experimental data with Blasius

correlation and Zigrang & Sylvester correlations for oil and

water single phase flow. It can be notice that experimental

results are in good agreement with Blasius correlation.

Table 2 shows uncertainty (%) of different parameters of the

study. The uncertainty calculations have been done using

Engineering Equation solver (EES) and it can be seen that the

uncertainty of pressure drop is about 2%.

Table 2 The Uncertainty Analysis Results

Parameter Instrument Uncertainty

% Water flow rate

(m3/hr)

MAG888 electromagnetic

flow meter

2.6

Oil flow rate

(m3/hr)

EF10 Ultrasonic flow meter 3.0

4 Copyright © 2014 by ASME

Pressure drop

(kpa)

Pressure transmitter

1.5

Diameter (mm) Varnier Caliper 0.01

Density

(kg/m3)

Viscometer 0.24

Friction factor

(F)

Software EES 3.13

Upward flow

Downward flow

FIGURE 4 PRESSURE DROP OF SINGLE PHASE OIL AND WATER.

Results and Discussions

Experiments were carried out to measure pressure

drop for water and oil single phase flow for different liquid

velocities (0.4 to 1.2 m/s). Inlet reference pressure was set at 1

bar. The experiments were repeated for different inclination

angles including; 0°, 15°, 30° (upward and downward flows).

The oil has a density of 795 Kg/m3 whereas the water has a

density of 998 kg/m3. Water and Oil viscosities are 0.798 Pa.s

and 1.56 Pa.s at 30°C, respectively.

Effect of upward inclination on pressure gradient

Figure 5 shows the pressure gradient of single phase

oil and water for upward flows. For horizontal flow the

pressure drop increases as the water velocity increases. This is

because friction head increases as the velocity increases. Also,

the pressure increases with increase in inclination. For 30 deg

inclination, the maximum value of the pressure drop for single

phase oil and water is 0.12 kpa/m and 0.14 kpa/m at water

velocity 1.17 m/s. The difference in the pressure drop is due to

the difference in the viscosities and densities of the two fluids.

FIGURE 5 PRESSURE GRADIENT OF SINGLE PHASE OIL

AND WATER FOR UPWARD FLOWS.

FIGURE 6 PRESSURE GRADIENT OF SINGLE PHASE OIL AND WATER FOR DOWNWARD FLOWS.

Effect of downward inclination on pressure gradient

Figure 6 shows the pressure gradient of single phase

oil and water for downward flows. As expected, pressure drop

for horizontal flows is similar to upward flows. Also, the

pressure increases with increase in inclination. For 30 deg

inclination, the maximum value of the pressure drop for single

phase oil and water is 0.17 kpa/m and 0.22 kpa/m at water

velocity 1.17 m/s. Again, it can be said that the difference in the

5 Copyright © 2014 by ASME

pressure drop is due to the difference in the viscosities and

densities of the two fluids. At lower velocities, the pressure

drop magnitude is lower at higher inclinations.

Pressure drop has been observed to increase

asymptotically with pipe inclination. Pressure drop of water has

been found to be higher than oil for all inclination (figure 5 &

6). This can be attributed to difference in viscosities of fluids.

Conclusions In the present study, oil and water single phase flow

experiments were carried out for different inclination angles

including; 0°, 15°, 30° (upward and downward flows) in 4 inch

diameter stainless steel pipe. Inlet liquid velocities were varied

from 0.4 to 1.2 m/s and reference pressure was set at 1 bar.

Pressure drop has been found to increase with increase in liquid

velocity. Also, pressure drop has been observed to increase

asymptotically with pipe inclination. Upward flows are

associated with high pressure drop as compared to downward

flows. The pressure drop of water is greater than that of oil for

all inclinations. This difference can be attributed to the

difference in fluid viscosities and densities. Measured pressure

drops were compared with existing empirical relations and

good agreement was noticed.

NOMENCLATURE A Cross-sectional area of the pipe [𝑚2] D Diameter of the pipe [ 𝑚 ] f Friction factor

ID Inner diameter [ 𝑚 ] L Length of the pipe [ 𝑚 ] 𝑄𝑎 Volumetric flow rate of air [ 𝑚3 𝑠⁄ ] 𝑄𝑤 Volumetric flow rate of water [ 𝑚3 𝑠⁄ ] Re Reynolds’s number

Greek Symbols 𝜌𝑎 Density of air [ 𝑘𝑔 𝑚3⁄ ] 𝜌𝑤 Density of water [ 𝑘𝑔 𝑚3⁄ ] 𝜇𝑎 Viscosity of air [ 𝑃𝑎. 𝑠 ] 𝜇𝑤 Viscosity of water [ 𝑃𝑎. 𝑠 ] Δ𝑃 Pressure drop [ 𝑃𝑎 ] Δ𝑃

Δ𝐿 Pressure gradient [ 𝑃𝑎/𝑚 ]

ACKNOWLEDGMENTS

The authors would like to acknowledge the support of

King Fahd University of Petroleum & Minerals for conducting

the present experimental research work.

REFERENCES

[1] Fan. Z., Ruder. Z. and Hanratry. T. J., 1993,

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HORIZONTAL PIPELINES,” Int. J. Multiph. Flow,

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[2] Greskovich E. J., and Shrier A. L., 1971, “Pressure

drop and holdup in horizontal slug flow,” AIChE J.,

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[3] Gopal M., 1998, “Development of a mechanistic model

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