Paper id 25201450

International Journal of Research in Advent Technology, Vol.2, No.5, May 2014
E-ISSN: 2321-9637
Performance Assessment of Heat Exchanger Tubes to
Improve the Heat Transfer Rate in Turbulant Flows by
Using Different Types of Twisted Tapes Inserts in
428
Tubes
Prof. Rahul A. Lekurwale1, Prof. Pravin R. Ingole2, Prof. Yogesh G. Joshi3, Prof. Pawan R. Ingole4
Mechanical Department1, 2, 3, 4, D.M.I.E.T.R, Wardha.1, 2, 3 ,J.D.I.E.T., Yavatmal
Email: rahul.lekurwale2011@gmail.com1, pravin_iingole@rediffmail.com2, ehacker00@gmail.com3,
pawaningole5@gmail.com
Abstract- The article presents an investigation of the effect of different twisted tapes like alternate clock wise,
counter clock wise(c-cc twisted tape),and serrated-edge insert on heat transfer and pressure loss behaviors in a
constant heat-fluxed tube. In the experiments, this twisted tape was inserted into the entire test tube with a
constant twist ratio in order to generate a continuous swirling water flow. Two geometry parameters of the
serrated twisted tape (STT) to be considered in the present work are the serration width ratio and the serration
depth ratio and in case of c-cc twisted tapes included three twist ratio y/w=30,4.0,and5.0 as well as each with
three twist angles, θ=300, 600 and 900. The measurements have been conducted for the water flow rate based on
Reynolds numbers in the turbulent regime from 4000 to 20,000.The experimental results of the STT inserted
tube are compared with those of the plain tube. The results show that the heat transfer rate in terms of Nusselt
number, Nu increases with the rise in the depth ratio but decreases with raising the width ratio. The heat transfer
rate is up to 72.2% and 27% relative to the plain tube. The thermal performance factor of the STT tube under
constant pumping power is evaluated and found to be above unity indicating that using the STT tube is
advantageous over the (twisted tube) TT tube or the plain tube. In case of c-cc twisted tape experiments have
been performed over a Reynolds number range under uniform heat flux condition, using water as working fluid.
In addition, correlation of the Nusselt number and friction factor for using the both twisted tapes are also
determined.
Keywords: clock wise, counter clock wise and serrated twisted tapes, heat transfer enhancement, twist ratio,
twist angle.
1. INTRODUCTION
Twisted tapes have been used extensively as a swirl
generator to enhance convection heat transfer rate in
finding the way to reduce the weight, size and cost of
heat exchanger systems in several industrial
applications such as chemical engineering process,
heat recovery process, air conditioning and
refrigeration systems, chemical reactors, power plant,
and nuclear reactor, etc. Tubes with twisted tape
insert are also an important group of the continuous
swirling flow device that generates twin swirling flow
motion over the whole tube length of flow at constant
heat transfer coefficient (h) and friction factor (f).
There are many devices used for producing swirl flow
in the tube such as helical vanes, helical grooved tube,
helical screw-tape, axial-radial guide vanes and snail
entry while the twisted tape is one of the most popular
group because of low cost, low maintenance, low
pressure loss and ease of construction. All of swirling
flow devices have been used to generate the tangential
velocity, thin the boundary layer. Insertion of
twisted-tapes in tubes is one such augmentation
technique. Fig.1 shows the layout of a full-length
twisted-tape insert inside a circular tube. they can be
easily employed to improve the thermal performance
of the existing systems. Twisted-tapes reduce the
dominant thermal resistance of the viscous stream and
reduce the required heat transfer surface area.
However, the thermal improvements are accompanied
by increased pressure drop. Date and Singham [1],
Date [2], and Hong and Bergles [3] investigated heat
transfer enhancement in laminar, viscous liquid flows
in tubes with uniform heat flux (UHF). Ray and Date
predicted the heat transfer in a square sectioned duct
fitted with twisted tape in both laminar and turbulent
flows. They found that the plain tube fitted with
serrated twisted tape provides heat transfer higher
than the plain tube without tape inserts One way for
enhancing heat transfer in a tube is by using a twisted
tape having serrate edges in order to increase mixing
or turbulence intensity and breaking down the
boundary layer apart from using continuous swirling
flow in the tube. The aim of the present work is to
investigate the heat transfer rate (Nu) and friction
factor (f) characteristics of continuous swirl flow
through a round tube fitted with serrated twisted tape
(STT) using the water as the test fluid. Aoyama et al.
[33,34] studied the laminar heat transfer in a horizontal
taining a twisted-tapes wirler. In the present study, the

E-ISSN: 2321-9637
429
alternate clockwise and counter clockwise twisted
tape inserts with novel design are therefore presented
and proposed for heat transfer enhancement. This
modified twisted tape is designed to offer periodic
change of swirl direction along the test tube, which is
expected to provide better mixing than the typical
one. The experiments are conducted to examine the
Nusselt number and flow friction characteristics in a
circular tube under uniform heat flux condition. In the
test, influences of (1) typical twisted tapes (single
twisting direction), (2) twisted-tapes with C–CC
arrangement at various twist ratios (y/w = 3.0, 4.0 and
5.0), and (3) twist angle (h = 30o, 60o and 90o), on
heat transfer rate (Nu), friction factor (f) and heat
transfer enhancement index ( ח) characteristics in a
heat exchanger are studied experimentally in the
Reynolds number range of 4000-20,000.The
geometrical details of all twisted tapes used in the
present work are depicted in Fig3..
2. EXPERIMENTAL DETAILS
2.1. C-CC Twisted Tapes
The C-CC. twisted-tapes were made of aluminum
strips with thickness of 1.0 mm (δ), width of 18 mm
and length of 1000mm.while being held under
tension. For typical twisted-tapes, the straight tapes
were twisted with three different twist lengths in 1800
rotation (y) in a single clockwise direction. On the
other hand, the novel alternate clockwise and counter-clockwise
twisted-tapes were obtained by
modification of typical tape via the following steps:
(1) for every two twist lengths, the tape was cut on
both sides with 4 mm depth of cut, (2) both sides at
the cut were twisted simultaneously to the required
different angles with respect to that of the former
twist length (called twist angle (θ)=300,600,900),which
is in arrangement for producing of swirl flow in
opposing direction with regard to that of the former
twist length (from clockwise to counterclockwise and
vice versa).The details of twisted-tapes are shown in
Fig1.
Fig1.Test tube fitted with twisted-tapes (a)The typical twisted-tapes
(TT),(b) C-CC.TT. with θ=300,(c) C-CC.TT.with θ=600,(d) C-CC.
TT with θ=900.
2.2. Serrated Twisted Tapes
The characteristic geometries of all tape are illustrated
inFig.2.Each of the twisted tape made of aluminium
was 1250 mm long, 0.8 mm thick and inserted into the
test tube having a uniform heat flux condition. The
test tube fitted withTT is presented in Fig3.The
geometrical dimensions of the STT where y is the
pitch length of 1800 twist, d is the tape thickness, W is
the tape width and D is the inner tube diameter; the
severity of the twist is usually referred to as a
dimensionless twist ratio, y/W. In each test run, the
STT was inserted into the whole length of the test
tube with a constant twist ratio, y/W=4.0. The tape
edge was cut to be serrate shape (V-cut) with two
geometry parameters:(1) the serration width ratio (w/
W = 0.1, 0.2 and 0.3) and (2) the serration depth ratio
(d/W = 0.1, 0.2 and 0.3). The details of the test
condition and twisted tape geometries are summarized
in Table 1.

E-ISSN: 2321-9637
430
Fig2. Test tube fitted with typical twisted tape(TT) or twisted tape
with serrated edge(STT):(a)TT,(b)STT at various serration width
ratio w/W, and (c) STT at various serration depth ratio,d/w.
2.3 Experimental Setup
A schematic diagram of the apparatus with the basic
components and fluid flow systems is presented in
Fig3.The loop consisted of a 0.5 hp centrifugal water
pump, Rota-meter for measurement of volumetric
water flow rate, and the heat transfer test section.The
copper test tube has an inside diameter of 19 mm, an
outside diameter of 22 mm, a tube thickness (t) of 1.5
mm and a length ( L) of =1000 mm. During the test,
the test tube is heated by continually winding flexible
electrical wires, providing a uniform heat flux
boundary condition. The electrical output power is
con- trolled by a variac transformer to obtain a
constant heat flux along the entire length of the test
section and by keeping the current less than 9 amps.
The outer surface of the test tube is well insulated to
minimize convective heat loss to surroundings, and
necessary pre- calculation are taken to prevent
leakages from the system.
2.4 Test condition and Method
In the apparatus setting bellow, the inlet cold water at
270C from a water pump was directed through the
Rota-meter and passed
to the heat transfer test section.The pressure drop of
the heat transfer test tube was measured with a
pressure trans-ducer. The volumetric water flow rates
from the centrifugal water pump were varied by
adjusting the globe valve and measured by the Rota-meter
situated upstream of the test tube. The inner and
outer temperatures of the water were measured at
certain points with a data logger unit in conjunction
with the RTD PT 100 type temperature sensors.
Fifteen thermocouple were tapped on the local wall of
the plain tube and the thermo-couples were placed
round the plain tube to measure the cir-cumferential
temperature variation, which was found to be
negligible. In which Re. ranges from 4000 to 20,000
for turbulant flow regimes.
3. DATA REDUCTION
In the present work, the water is used as working fluid
and flowed through a circular tube with uniform heat
flux conditions. At steady state, the heat absorbed by
cold water is assumed to be equal to the convective
heat transfer from the test section which can be
expressed as:
Qwater = Qconv. ,Where Qwater = MCpw(T0-Ti),
The convective heat transfer from the test
section can be written by:
Tb = (T0+Ti)/2 Ťw= Σ Tw / 15
in which Tw is the local inner wall surface
temperature.
Fig 3 Reynolds Number Vs Nusselt Number
4. RESULT AND DISCUSSION
4.1. Effect of alternate clockwise and counter-clockwise
twisted tape
Effect of the novel alternate C–CC twisted tapes at
various twist ratios, y/ w = 3.0, 4.0 and 5.0, on the
Nusselt number.For all runs, Nusselt number is
consistently increased with increasing Reynolds
number. This is due to the fact that the rise of
Reynolds number leads to an increase in degree of
turbulenc intensity

E-ISSN: 2321-9637
431
Fi4.comparisons between Re. and Nu. Number with different twist
angle.
4.2.Effect of serrated twisted tapes
Effects of the STT at different serration width
(w/W=1.0,2.0,and3.0) and depth ratios(d/W = 1.0,2.0
and 3.0) covering a wide variation of flow rates
corresponding to the range of 4000<Re<20,000.
4.3. Thermal performance
The value of the thermal performance factor must be
greater than unity .
Fig5.Effect of the serration depth ratio (d/w) on thermal
performance factor.
It is visible that at lower Reynolds number the
increase in the thermal performance factor is
comparatively
higher, but at higher Re, it is smaller.The
experimental results show that the thermal
performance factor vary between 0.98 and 1.17, 0.97
and 1.12, and 0.96 and 1.09 for the width ratio,
w/W=1.0, 2.0 and 3.0, Respectively.The comparison
of thermal performance factors in tubes equip-ped
with the present STT and other tape inserts in
previous work is shown in Fig8.
(Fig6.Comparison of thermal performance of the present
STT with previous work)
5.CONCLUSION
In the present work, an experimental study has been
conducted to investigate the heat transfer

E-ISSN: 2321-9637
432
enhancement by means of twisted-tape inserts with
alternate C–CC twisted and serrated twisted tapes
arrangement in a circular tube under a uniform heat
flux condition.From the experimental results, the
conclusions can be drawn as follows:
1. In the presence of novel alternate C–CC
twisted and STT tapes, the peri-odic change of
swirl direction and gives to superior chaotic
mixing with high turbulance flow for
increasing the heat transfer rate compared with
the plane tube.
2. Over the range studied, the Nusselt numbers
for the tube withC–CC twisted and serrated
twisted tapes. higher than those for the plane
tube.
3. The heat transfer enhancement
index,performance factor for STT.tends to
increase with decreasing Reynolds number for
all tapes inserts.
REFERENCES
[1] G.C. Kidd Jr., Heat transfer and pressure drop for
nitrogen flowing in tubes containing twisted-tapes,
AIChE J. 15 (1969) 581–585.
[2] O.H. Klepper, Heat transfer performance of short
twisted-tapes, AIChE J. 35 (1972) 1–24.
[3] A. Dewan, P. Mahanta, K. Sumithra Raju, P.
Suresh Kumar, Review of passive heat transfer
augmentation techniques, J. Power Energy 218
(2004) 509– 525
[4] S.W. Chang, Y.J. Jan, J.S. Liou, Turbulent heat
transfer and pressure drop in
tube fitted with serrated twisted-tape, Int. J. Therm.
Sci. 46 (5) (2007) 506–518.
[5] S.W. Chang, T.L. Yang, J.S. Liou, Heat transfer
and pressure drop in tube with broken twisted-tape
insert, Exp. Therm. Fluid Sci. 32 (2) (2007) 489–
501.
[6] Ayd ın Durmus, Ayla Durmus, M. Esen,
Investigation of heat transfer and pressure drop in
a concentric heat exchanger with snail entrance.
Appl. Therm. Eng 22 (2002) 321e 332.
[7]S.Eiamsaard,P.Promvonge,Enhancement of heat
transfer in a tube with regularly-spaced helical
tape swirl generators. Solar Energy 78 (4) (2005)
483 e494
[8] K.S. Yajnik, M.V. Subbaiah,

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