Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: 15.3.2 - Effect of Return Bends on Kerosene-Water Flow Through a Horizontal Pipe
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Title: 15.3.2 - Effect of Return Bends on Kerosene-Water Flow Through a Horizontal Pipe Experimental Methods for Multiphase Flows
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Ravi, P.
Sharma, M.
Ghosh, S.
Das, G.
Das, P.K.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
Subject: oil-water flow
return bend
Abstract: In the present work, effect of return bends on the hydrodynamics of kerosene and water flow through horizontal conduits has been studied. Extensive experiments are performed with two different types of bends namely U bend and rectangular bend. It is observed that the type of return bend has a strong influence on the downstream flow patterns. It is also noted that the rectangular bend increases the pressure drop at bend in comparison with U bend. The loss coefficients are estimated for each case which are found to be independent of flow patterns in both the cases.
General Note: The International Conference on Multiphase Flow (ICMF) first was held in Tsukuba, Japan in 1991 and the second ICMF took place in Kyoto, Japan in 1995. During this conference, it was decided to establish an International Governing Board which oversees the major aspects of the conference and makes decisions about future conference locations. Due to the great importance of the field, it was furthermore decided to hold the conference every three years successively in Asia including Australia, Europe including Africa, Russia and the Near East and America. Hence, ICMF 1998 was held in Lyon, France, ICMF 2001 in New Orleans, USA, ICMF 2004 in Yokohama, Japan, and ICMF 2007 in Leipzig, Germany. ICMF-2010 is devoted to all aspects of Multiphase Flow. Researchers from all over the world gathered in order to introduce their recent advances in the field and thereby promote the exchange of new ideas, results and techniques. The conference is a key event in Multiphase Flow and supports the advancement of science in this very important field. The major research topics relevant for the conference are as follows: Bio-Fluid Dynamics; Boiling; Bubbly Flows; Cavitation; Colloidal and Suspension Dynamics; Collision, Agglomeration and Breakup; Computational Techniques for Multiphase Flows; Droplet Flows; Environmental and Geophysical Flows; Experimental Methods for Multiphase Flows; Fluidized and Circulating Fluidized Beds; Fluid Structure Interactions; Granular Media; Industrial Applications; Instabilities; Interfacial Flows; Micro and Nano-Scale Multiphase Flows; Microgravity in Two-Phase Flow; Multiphase Flows with Heat and Mass Transfer; Non-Newtonian Multiphase Flows; Particle-Laden Flows; Particle, Bubble and Drop Dynamics; Reactive Multiphase Flows
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Volume ID: VID00374
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Holding Location: University of Florida
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Resource Identifier: 1532-Ravi-ICMF2010.pdf

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7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

Effects of return bends on kerosene-water flow through a horizontal pipe

P.Ravil, M. Sharma2, S.Ghosh', G. Dasl', P. K.Das2

1 Department of Chemical Engineering, IIT Kharagpur
2 Department of Mechanical Engineering, IIT Kharagpur
Kharagpur 721302, India
Email of the presenting author: g.=l !~cjc.7h i !-cl.ic il !in.I

Keywords: oil-water flow, return bend


In the present work, effect of return bends on the hydrodynamics of kerosene and water flow through horizontal conduits has
been studied. Extensive experiments are performed with two different types of bends namely U bend and rectangular bend. It
is observed that the type of return bend has a strong influence on the downstream flow patterns. It is also noted that the
rectangular bend increases the pressure drop at bend in comparison with U bend. The loss coefficients are estimated for each
case which are found to be independent of flow patterns in both the cases.

four U-type return bends with tube diameter 3 and 5.07
mm and curvature ratio ranging from 3.91 to 8.15. They
have proposed a correlation for two-phase friction factor.
Wang et al. (2004) have observed the influence of return
bend on the flow patterns during air-water flow in a small
diameter tubes. They noted the formation of annular flow
to be favored for tube diameters greater than 3 mm.
Similar study is also reported by Wang et al. (2003). Wang
et al. (2005) have performed experiments to study
two-phase slug flow across small diameter tubes in
presence of vertical U-type return bends. They have also
proposed correlations to predict the variation of translation
velocity within the bends. Subsequently, Chen et al. (2007)
carried out experiments to study single-phase and
two-phase pressure drop for oil-R134a mixture flowing in
U type bends made of tubes of 5.07 and 3.25 mm diameter
and 5.18 to 3.91 curvature ratios. They have reported that
the ratio of two-phase pressure gradient of the U-bend to
the straight tube is about 2.5-3.5. The ratio increased
slightly with increasing oil concentration and vapor quality.
Similar work was also been performed by Chen et al.
(2008) in vertical and horizontal arrangements of a U-bend
with inner diameter of 5.07 mm and a curvature ratio of 5.

However, to the best of authors knowledge no information
is available on oil-water flow through bends. The present
work reports extensive experiments on low viscous
oil-water upflow through return bends installed in a
horizontal pipe. Two bend geometries viz a U shape and a
rectangular shape ( ) have been used for this purpose.

Nomenclatu re

Pipe diameter
gravitational constant (ms ')
Frictional energy loss per unit mass


Flow of liquid -liquid mixtures is frequently encountered
in process industries. As a result, the past few decades have
observed a growing interest in the hydrodynamics of
oil-water flow. In case of low viscous oil-water systems,
the investigations are primarily confined to the estimation
of flow pattern and pressure drop [Hasson et al. (1970),
Chakrabarti et al. (2005), Jana et al. (2006 a, b), Mandal et
al. (2007)] through horizontal and vertical pipes of uniform
cross section. Not much is known about the
hydrodynamics and loss coefficients when such flow
encounters a return bend in its flow path.

A survey of the past literature shows that the majority of
the works performed with return bends are confined to
gas-liquid flows. Researchers have reported the effect of
return bend on flow distribution for air-water flows (Usui
et al.(1980), Usui et al. (1983), Chen et al. (2002),Wang et
al.(2005)) as well as the bend pressure drop during flow of
various refrigerant and their vapor (Geary 1975, Chen et
al.2007, Chen et al.2008, Domanski and Hermes 2008).

One of the earliest studies dates back to Geary (1975),
who performed experiments with liquid-vapor flow of
R-22 in bends having inner diameters of 11.4 mm and 11.6
mm. He correlated two-phase pressure drop in return bends
with single phase pressure drop of vapor. Wang et al.
(2003) have investigated flow patterns for air-water
mixtures inside smooth tubes of diameter 3, 4.95, and 6.9
mm in presence of horizontal return bends of curvature
ratios ranging from 3.2 to 7.1. They observed that the flow
pattern transition from stratified to annular was not
prominent with the decrease in curvature ratio and have
attributed this to the influence of surface tension and length
of the developing region. Chen et al. (2004) reported
single-phase and two-phase frictional data for R-410A in

Experimental Facility

A schematic of the experimental setup is depicted in Figure
1. The set up comprises of two test rigs of 0.012 m
diameter acrylic resin tubes. As shown in the figure, two
identical horizontal sections of 4 m length are connected
by a U shaped bend in one case and a rectangular bend
(denoted as n for the ease of reference) in the second
case. The distance between two horizontal pipes is 0.2 m
for both the cases. The curvature ratio (R/D) of the U bend
is 8.33. Kerosene ( p=787 kg/m3, pu=0.0012 Pa-s), and
water are used as the test fluids.

7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

flowmeter (E) for water and rotameter (R) for kerosene.
Both the flowmeters have been calibrated before use and
their calibration is checked from time to time. The
rotameter ranges from 0 to 3.33 x 10-4 m3/S With a least
count of 3.33 x 10-6 m3/s and the Electromagnetic
fl0Wmeter from 0 to 4.17x10 -4 m3/S With a least count of
4.17 x10 -6 m3/s. The accuracy of measurement using the
rotameter lies within 2 % as supplied by the manufacturer
and also verified by calibration and that of the
Electromagnetic flow meter is 10.5 % as supplied by the
manufacturer. Accordingly, the maximum experimental
errors in measuring superficial velocities are & 1.67% and
& 0.67% for kerosene and water respectively.
Two three way valves (Vl and V2 in Figure 1) direct the
flow of two liquids to either of the test rigs. They are
introduced at the entry section through a specially designed
nozzle where the oil flows centrally while water is injected
in the annular space. After the test section, the two-phase
mixture enters the separator (S) where they are gravity
separated and recycled back to their respective storage
The flow patterns as observed for various combinations of
oil and water superficial velocities are noted visually and
photographed by a high-speed digital camera (DSCH9,
SONY). Photographs are taken at a distance of 1.5 m
from the entry section as well as at bend and downstream
sections as shown in Figure 1. View boxes are installed in
the photographic section to minimize the effects of
reflection and refraction by the walls of the cylindrical
pipe. The pressure drop is noted with differential pressure
transmitter (Honeywell, STD120) at the upstream, bend
and downstream sections. The accuracy in measuring the
pressure drop is +0.5 % .The first pressure tap (PTI) is
located at a distance of 120D from the entry section and
the last tap (PT6) is at a distance of 120D from the outlet
(Figure 1). The distance between two taps at the upstream
(PT1 and PT2) and downstream section (PT~and PT6) is
100D. Two taps PT3 and PT4 are also provided to measure
the pressure drop across the bend.

Results and Discussion

Effect of Bend geometry on flow pattern:

In order to understand the influence of return bends on the
phase distribution, the flow patterns in the upstream,
downstream and at the bend sections are observed. The
schematic and representative photographs of various flow
regimes encountered at upstream and downstream section
during the flow of kerosene and water through both the
bends are depicted in Figure 2.
As shown in Figure 2, the flow regimes observed at the up
and downstream of both the bends are wavy stratified, plug,
kerosene dispersed and water dispersed. Wavy stratified
flow pattern is observed at low to moderate water velocity
for all kerosene flowrates. It is characterized by a wavy
interface between kerosene and water (Figure 2a). At a
relatively higher water velocity kerosene forms tiny drops
in a continuous water medium. This is known as kerosene
dispersed regime (Figure 2c). Reverse interfacial
configuration is observed for low water and high kerosene





Loss coefficient
Pressure gradient (Pa/m)
Volumetric flow rate
Superficial phase velocity
Density (kg/ m-3)
Viscosity (Pas)
Insitu volume fraction
Inlet volume fraction


Figure 1: Schematic of experimental set up

Centrifugal pumps (Pl) and (P2) with maximum discharge
flow rate of 1.3 X10 -3 m3/s and head of 294.3 kPa are used
to pump kerosene and water through the test rigs. The
inflow of the test fluids are metered using Electromagnetic

Flow regimes IShematic htgrps

(b) Plug flow

( Krosene ,

(d) Water

Figure 2: Schematic and representative photographs of
flow patterns observed at up and down streams of bends

7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

diameter tube is provided by Mandal et al. (2007).
The range of existence of the aforementioned flow regimes
have been shown in the form of maps in Figure 3a-e. The
maps have been constructed in terms of superficial
velocities of oil (Usk) and water (Usw) as their axes. Part a
of the figure depicts the upstream flow pattern map for
both bend geometry.
The influence of bend geometry on the downstream flow
pattern is noted by comparing Figures 3a-e. A few
representative photographs of the downstream flow
patterns under similar phase velocities, as observed during
upflow through U and n bend have been presented are
in Figure 4 to highlight some of the differences.

Upstream Downstream (U bend) Downstream (f bend)

Usk=0 3 m/s, Usw-0 75 mis

Wavy trhatlfied flow
Wavy stratlfied flowWaedsesd
Usk=1 0 m/s, Usw-0 15 m/s

~~~~~~Wavy stratified flwWv tate ow
Usk=0 75 m/s, Usw-0 6 m/s

Figure 4: Flow patterns observed at up and down stream
of U and n bends

In a nbend kerosene dispersed flow exists for a
larger range at the bend and downstream as compared
to U bend.
* The water dispersed regime is not observed at the U
bend but occurs at the Pl bend as well as its
downstream sections. This can be attributed to the
increased effect of turbulence introduced by sharp
changes in flow direction in the latter case.
* The plug flow pattern is noted to exist at higher Usw
at the U bend as compared to other geometry. This is
further evident from the photographs of Figure 4.
* The phenomena of film inversion, is observed at the U
bend but not the 1-- bend. This can be attributed to
presence of centrifugal forces. It is also reported by
Usui et al. (1983) for air-water flow through retun

Effect of Bend geometry on pressure drop

Next, attempts have been made to understand the effect of
return bends on the frictional pressure gradient and loss

a) Frictional pressure gradient:

In this section, a comparison of the pressure gradient at
upstream, bend and downstream sections of the two bend
geometries are made. The two phase pressure gradient at
bend section has two components frictional and
gravitational given below as:

flowrates where water form
kerosene medium. This flow
dispersed (Figure 2d).

small drops in continuous
regime is known as water

9 4I 44 46 44
(a) Up stream

UBend (b) Downstream

FIBend (d) Downstream
n Wavy stratified a


(c) Bend section

c~ c

(e) Bend section
Core-annular flow' Plug flow

x Kerosene dispersed -- Water dispersed

Figure 3: Flow pattem map

It is observed at the downstream and bend section incase of
kerosene-water flow through rectangular bend. Plug flow
appears as a transition regime between wavy stratified and
kerosene dispersed. In this regime, a well defined bullet
shaped plugs of kerosene are observed in a continuous
water medium (Figure 2b).
A detailed description of the patterns in a 0.0127 m

7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

dp. dp. dp
( )f ()+( )g

3500 -

E 2500 -
PI 2000 -

1500 -

o Way hrtfiedflow
S xKa~rosendirspene

The frictional pressure gradient at bend in case of kerosene-
water upflow can be obtained by subtracting the
gravitational component of two-phase mixture from the
measured total pressure gradient as:

(-dp) = k a k (2)
dz dz

Where (ip~d can be measured using the pressure
transmitter, ak is the insitu volume fraction of the kerosene

and p,,, pk are the densities of water and kerosene
respectively and g is the acceleration due to gravity. a is
taken as the inlet volume fraction in case of slug, kerosene
and water dispersed.


0 2 4 6 8
(c Downstream (U type)

--- Usk=~lsrds~

a lu fow
:~- Waterdispened

12000 -

10000 -

8000 -

6000 -






- VsW.Is mte
- Usk-0.45 m/s
- Usk =19 0 Ms



a 2


3000 -

2500o -

2000 -

S1000 -(

5001 -

(d) Bend action (n type)

-Usk-0.45 m/s
-- UA=00Om/s
o Wavy stratified fo

0 2 4 6 8

(a) Upstream

8000 -
10 -
7000 -

5000 -
4000 -

7 /
' -"

0 2 4 6 8
(e) Downstream (n type)

Figure 5: Pressure gradient observed in U and n bend
0 2 4 6 8 at different sections

(b) Bend section (U type)

In case of core annular flow at bend it can be obtained using
the empirical correlation proposed by Arney et al. (1993) as:

aw = B[1+ 0.3 5(1- B)] (3)

Where it is the inlet water fraction defined as:



Ccharnwlsr ie"'

7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

Qk and Q denote the volumetric flow rate of kerosene and
total two phase mixture respectively.

Figures 5a-e depict the variation of frictional gradient as a
function of water to kerosene volumetric flowrate ratio
(Qw/IQk) with Usk as parameter.

> The figures show that pressure gradient for a
particular kerosene flowrate increases as the flow
of water is increased and higher gradients are
observed for higher kerosene flow rates.
> The magnitude of frictional gradient at bend are
always higher than the corresponding pressure
drop in the downstream section.
> Moreover the rectangular bend has higher
frictional pressure gradient than U bend due to
sharp changes in direction introduced by the

SPlug flow
* Kerosene dispersed
*Colre-annular flow
- Water dispersed
x Singlephase






1.5 -

1 .

0.5 -


10000 15000
b) E- Bend

Figure 5: Pressure loss coefficient

b) Corresponding loss coefficients:

The loss coefficients are defined as:

The trend of all the figures shows an inverse relation of the
loss coefficient with Reynolds number. This is mn
agreement with the observations of Ito et al. (1960) The
l0SS coefficients for rectangular bend are always higher
than that of U bend. It can also be noted that the loss
coefficients are independent of flow patterns.


From the above study it can be concluded that
*Type of return bend influences the flow regimes
at downstream and at the bend section. Water in
oil dispersed flow regime is observed at bend and
downstream section in case of FI bend.
However this regime is not observed in U bend
within the same experimental condition. Also
kerosene becomes dispersed in water at a lower
water velocity in case of rectangular bend as
compared to U bend.
*Because of a sharp change in direction,
rectangular bend causes a higher frictional
pressure drop at bend section.


Arney, M.S, Bai, R., Guevara, E., Joseph, D.D, Liu, K.
Friction factor and hold up studies for lubricated
pipelining-1 Experiments and correlations. Int. J of
Multiphase Flow, Vol. 19, 1061-67 (1993).

Balakhrisna, T., Ghosh, S., Das, G., Das, EK. Oil-Water
flows through Sudden Contraction and Expansion in a
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Chakrabarti, D.E, Das, G.., Ray, S. Pressure drop in
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prediction. Chem. Eng. Technol., Vol. 28, 1003-1009

hf =k Um2

Where h, can be estimated by applying Bemoulii's eqn
across the bend. The error in estimating loss coefficients in
case of kerosene-water system as calculated from Holman
(1989) and described in Balakhirshna et al. (2010) lies
within 4.4 %. Figures 6a-b represent the variation of k with
Reynolds number for single and two-phase flow through
both the bend geometries. The Reynolds number for
two-phase flow is defined as Re =m weeP

Pm and Um are the mixture viscosity, density and velocity
respectively and D is the pipe diameter. From Figures 6a-b
it can be noted that in case of U bend the average value of
loss coefficients for single and two-phase system are
comparable and can be depicted by a single best-fit line.
However in rectangular bend single-phase loss coefficients
are higher than two-phase values.


Plug flow "
SKerosene dispersed
* Core-annular flow
SSingle phase

soooO loose0 MIso
a) U bend

zoooo0 zso(O

20000 25000

7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

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