Download Heat Transfer Enhancement in a Circular Tube Twisted with Swirl

Proc. of the 3rd International Conference on Advances In Mechanical Engineering, January 4-6, 2010
S.v. National Institute of Technology, Surat - 395 007, Gujarat, India
Heat Transfer Enhancement in a Circular Tube Twisted with
Swirl Generator: A Review
Kumbhar D.G.1, Dr. Sane N.K.2,
'Assistantr'rofessor Department Of Mechanical Engg. B.V.U.C.O.E., Pune.
2 Professor, Department Of Mechanical Engg JSPM C.O.E., Pune
Corresponding author (Email:[email protected])
The present paper is a review of research work in last decade on heat transfer
enhancement in a circular tube. In the present paper emphasis is given to works
dealing with twisted tape inserts because according to the recent studies, these
are known to be economic heat transfer enhancement tool. The thermo hydraulic
performance of twisted tape insert depends on the flow conditions i.e., laminar or
turbulent flow apart from the insert configuration. The present review is
organized separately for laminar & turbulent flow.
1.
Introduction
The development of high performance thermal systems has stimulated interest in
methods to improve heat transfer. The study of improved heat transfer is referred to as heat
transfer enhancement, augmentation or intensification.
The performance of conventional heat exchanger can be substantially improved by a
number of enhancement techniques. A great deal of research effort has been devoted to
developing apparatus and performing experiments to define the conditions under which an
enhancement technique will improve heat transfer. Heat transfer enhancement technology
has been widely applied to heat exchanger applications in refrigeration, automobile, process
industries etc. The goal of enhanced heat transfer is to encourage or accommodate high heat
fluxes. This result in reduction of heat exchanger size, which generally leads to less capital
cost. Another advantage is the reduction of temperature driving force, which reduces the
entropy generation and increases the second law efficiency. In addition, the heat transfer
enhancement enables heat exchanger s to operate at smaller velocity, but still achieve the
same or even higher heat transfer coefficient. This means that a reduction of pressure drop,
corresponding to less operating cost, may be achieved. All these advantages have made heat
transfer enhancement technology attractive in heat exchanger applications. For shell and tube
heat exchangers, the tube insert technology is one of the most common heat transfer
enhancement technologies, particularly for the retrofit situation. With tube insert technology,
additional exchangers can often be avoided and thus significant cost saving becomes
possible.
Furthermore as a heat exchanger becomes older, the resistance to heat transfer
increases owing to fouling or scaling. These problems are more common for heat exchangers
used in chemical industries and marine applications. In this case the heat transfer rate can be
improved by introducing a disturbance in the fluid flow by different enhancement technologies
(breaking the viscous and thermal boundary layer).
In this paper, a review of heat transfer enhancement tool i.e. twisted tape swirl
generator is done, for laminar and turbulent flow. Since it is most commonly used
enhancement tool. This paper also gives performance evaluation criteria for a twisted tape
swirl generator. Finally it is expected to be the pioneer source as an intensive literature review
for twisted tape swirl generator.
2.
Classificationof AugmentationTechniques
They are broadly classified into three different categories:
1. Passive Techniques
2. Active Techniques
3. Compound Techniques.
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Proc. of the 3'd International Conference on Advances in Mechanical Engineering, January 4-6, 2010
SV Nationallns!itute of Technology, Sura! - 395 007, Gujarat, India
1) Passive Techniques-These techniques do not require any direct input of external power;
rather they use it from the system itself which ultimately leads to an increase in fluid pressure
drop. They generally use surface or geometrical modifications to the flow channel by
incorporating inserts or additional devices. They promote higher heat transfer coefficients by
disturbing or altering the existing flow behavior except for extended surfaces. Heat transfer
augmentation by these techniques can be achieved by using; treated surfaces, rough
surfaces, extended surfaces, displaced enhancement devices, swirl flow devices, etc.
2) Active Techniques-In these cases, external power is used to facilitate the desired flow
modification and the concomitant improvement in the rate of heat transfer. Augmentation of
heat transfer by this method can be achieved by mechanical aids, surface vibration, and
electrostatic fields, etc.
3) Compound Techniques-When any two or more of these techniques are employed
simultaneously to obtain enhancement in heat transfer that is greater than that produced by
either of them when used individually, is termed as compound enhancement. This technique
involves complex design and hence has limited applications.
3.
Review
3.1
Twisted tape swirl generators
To enhance the heat transfer rate, some kind of insert is placed in the flow passages
and they also reduce the hydraulic diameter of the flow passages. Heat transfer enhancement
in a tube flow blockages, partitioning of the flow and secondary flow. Flow blockages increase
the pressure drop and leads to viscous effects, because of a reduced free flow area. The
selection of the twisted tape depends on performance and cost. The performance comparison
for different tube inserts is a useful complement to the retrofit design of heat exchangers.
Therefore this paper concentrates on the review of thermal and hydraulic performance for a
twisted tape insert, in the retrofit situation is done. Fig 1 shows geometry of twisted tape
inserts.
-].3
Fig.1(a) Full length Twisted tape insert
(b) Regularly spaced Twisted tape insert
An extensive literature review of heat transfer enhancement in laminar flow and
turbulent flow using twisted tape insert is discussed in following sections.
3.2
Twisted tape insert in laminar flowYadav [1] studied influences of the half length twisted tape insertion on heat transfer
& pressure drop characteristics in a U-bend double pipe heat exchanger, experimentally. The
results obtained from the heat exchangers with twisted tape insert are compared with those
without twisted tape i.e. Plain heat exchanger. The experimental results revealed that the
increase in heat transfer rate of the twisted-tape inserts is found to be strongly influenced by
tape-induced swirl or vortex motion. The heat transfer coefficient is found to increase by 40%
with half-length twisted tape inserts when compared with plain heat exchanger. It was found
that on the basis of equal mass flow rate, the heat transfer performance of half-length twisted
tape is better than plain heat exchanger.
Sheeba et al. [2] Experimental investigation of heat transfer, friction factor and
thermal performance of thermosyphon solar water heater system fitted with helical twisted
tape of various twist ratios has been performed and presented. Conclusions made from the
results show that heat transfer enhancement in twisted tape collector is higher than the plain
tube collector with minimum twist ratio and gradually decreases with increase in twist ratio.
The overall thermal performance of twisted tape collector is found to increase with increase in
solar intensity.
Un and Wang [3] investigated numerically sensitivity. of, the laminar convective heat
transfer in a circular tube fitted with twisted tape. The effects of conduction in the tape on the
Nusselt number, the relationship between the absolute vorticity flux and the Nusselt number,
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Proc.of the 3rd InternationalConferenceon Advancesin MechanicalEngineering,January4-6, 2010
S.v. NationalInstituteof Technology,Surat - 395007, Gujarat, India
the sensitivity of heat transfer enhancement to the thermal boundary conditions by using
secondary flow, and the effects of secondary flow on the flow boundary layer were discussed.
The results reveal that for fully developed laminar heat convective transfer, different tube wall
thermal boundaries lead to different effects of conduction in the tape on heat transfer
characteristics
Bharatdwaj at al. [4] experimentally determined pressure drop and heat transfer
characteristics of flow of water in a 75-start spirally grooved tube with twisted tape insert are
presented. Laminar to fully turbulent ranges of Reynolds numbers have been considered. The
grooves are clockwise with respect to the direction of flow. Compared to smooth tube, the
heat transfer enhancement due to spiral grooves is further augmented by inserting twisted
tapes having twist ratios Y= 10.15, 7.95 and 3.4.
Naphon [5] investigated the heat transfer characteristics and the pressure drop in
the horizontal double pipes with twisted tape insert. The results obtained from the tube with
twisted insert are compared with those without twisted tape. Non-isothermal correlations
based on the data gathered during this work for predicting the heat transfer coefficient and
friction factor of the horizontal pipe with twisted taped insert are proposed.
Ray and Date [6] derived a correlation for the friction factor and Nusselt number for a
square duct from the predicted data. They compared the correlation for the friction factor with
experimental data and the agreement was found to be within +10 per cent.
Suresh Kumar at al. [7] investigated the thermo hydraulic performance of twisted tape
inserts in a large hydraulic diameter annulus. The thermo hydraulic performance in laminar
flow with a twisted tape is better than the wire coil for the same helix angle and thickness
ratio.
Wang and Sunden [8] reported correlations for ethyl glycol and polybutene (Pr. No.
10000-70000)., They also concluded by considering the overall enhancement ratio, twisted
tape is effective for small Prandtl number fluids and wire coil is effective for high Prandtl
number fluids.
Saha et al. [9, 10, 11] reported experimental data on a twisted tape generated laminar
swirl flow friction factor and Nusselt number for a large Prandtl number (205- 518) and
observed that, on the basis of a constant pumping power, short-length twisted tape is a good
choice because in this case swirl generated by the twisted tape decays slowly downstream
which increases the heat transfer coefficient with minimum pressure drop, as compared with a
full-length twisted tape.
3.3
Twistedtape insert in turbulentflowEiamsa-ard et al.[13] investigated heat transfer, flow friction and thermal performance
factor characteristics in a tube fitted with delta-winglet twisted tape, using water as working
fluid are investigated experimentally. Influences of the oblique deJta-winglet twisted tape (0OWT) and straight delta-winglet twisted tape (S-OWT) arrangements are also described. The
experiments are conducted using the tapes with three twist ratios (ylw = 3, 4 and 5) and three
depth of wing cut ratios (DR = dlw = 0.11, 0.21 and 0.32) over a Reynolds number range of
3000-27,000 in a uniform wall heat flux tube. The obtained results show that mean Nusselt
number and mean friction factor in the tube with the delta-winglet twisted tape increase with
decreasing twisted ratio (y/w) and increasing depth of wing cut ratio (DR).
Smith Eiamsa-ard et al. [14] they presented an experimental study on the mean
Nusselt number, friction factor and enhancement efficiency characteristics in a round tube
with short-length twisted tape insert under uniform wall heat flux boundary conditions. In the
experiments, measured data are taken at Reynolds numbers in a turbulent region with air as
the test fluid. The full-length twisted tape is inserted into the tested tube at a single twist ratio
of y/w = 4.0 while the short-length tapes mounted at the entry test section are used at several
tape length ratios (LR = lsilt) of 0.29, 0.43, 0.57 and 1.0 (full-length tape). The experimental
result indicates that the short-length tapes of LR = 0.29, 0.43 and 0.57 perform lower heat
transfer and friction factor values than the full-length tape around 14%, 9.5% and 6.7%; and
21%, 15.3% and 10.5%, respectively.
Eiamsa-ard et at. [15] They investigated the application of a mathematical model for
simulation of the swirling flow in a tube induced by loose-fit twisted tape insertion. Effects of
the clearance ratio defined as ratio of clearance between the edge of tape and tube wall to
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Proc. of the 3m International Conference on Advances in Mechanical Engineering, January 4-6, 2010
S.V. National Institute of Technology, Surat - 395 007, Gujarat, India
tube diameter (CR = clD = 0.0 (tight-fit), 0.1, 0.2 and 0.3) on heat transfer enhancement (Nu),
friction factor (f) and thermal performance factor (rJ) are numerically investigated for twisted
tapes at two different twist ratios (y/w = 2.S and S.O)
Sharma et al. (16) conducted experiments to evaluate heat transfer coefficient and
friction factor for flow in a tube and with twisted tape inserts in the transition range of flow with
AI203 nanofluid are conducted. The results showed considerable enhancement of convective
heat transfer with Al203 nanofluids compared to flow with water. It is observed that the
equation of Gleninski applicable in transitional flow range for single-phase fluids showed
considerable deviation when compared with values obtained with nanofluid.
Hong et al. (17) studied Pressure drop and compound heat transfer characteristics of
a converging-diverging tube with evenly spaced twisted-tapes (CD- T tube) have been
investigated experimentally. Swirl was generated by evenly spaced twisted-tape elements
which vary in twist ratio and rotation angle. Space ratio also has an important effect on the
characteristics. For Comparison, experiments in a smooth circular tube and a convergingdiverging (CD) tube without twisted-tapes were carried out. The results show that the twistedtape with twist ratio y=4.72 and rotation angle 8= 180 has the best performance among the
four types of twisted-tapes presented in this paper.
Eiamsa-ard et al. (18) In the present study, the influences of twin-counter/co-twisted
tapes (counter/co-swirl tape) on heat transfer rate (Nu), friction factor (f) and thermal
enhancement index ('7) are experimentally determined. The twin counter twisted tapes (CTs)
are used as counter-swirl flow generators while twin co-twisted tapes (CoTs) are used as coswirl flow generators in a test section. The tests are conducted using the CTs and CoTs with
four different twist ratios (y/w = 2.S, 3.0, 3.S and 4.0) for Reynolds numbers range between
3700 and 21,000 under uniform heat flux conditions
Thianpong et al. (19) they investigated experimentally heat transfer and friction
characteristics for water, ethylene glycol, and ISO VG46 turbine oil flowing inside four tubes
with three-dimensional internal extended surfaces and copper continuous or segmented
twisted-tape inserts. During the experiments, Prandtl numbers ranged from 5.5 to 590 and
Reynolds numbers from 80 to SO,OOO.The experimental results show that this compound
enhanced heat transfer technique, a tube with three-dimensional internal extended surfaces
and twisted-tape inserts, is of particular advantage to enhance the convective heat transfer for
the laminar tube side flow of highly viscous fluid
Eiamsa-ard et al. (20) presented a comparative investigation of enhanced heat
transfer and pressure loss by insertion of single twisted tape, full-length dual and regularlyspaced dual twisted tapes as swirl generators, in a round tube under axially uniform wall heat
flux (UHF) conditions. The investigation encompassed the Reynolds number based on the
inlet tube diameter (0) ranging from 4000 to 19,000. The experiments are performed using
single twisted tapes and full-length dual twisted tapes with three different twist ratios
(y/w =·3.0, 4.0 and 5.0) and also regularly-spaced dual twisted tapes with three different
space ratios (sID = 0.7S, 1.S and 2.25). The effects of major parameters on heat transfer and
friction factor are discussed and the results from both single and dual twisted tape inserts are
compared with those from the plain tube.
0
4.
Conclusions
A twisted tape insert mixes the bulk flow well and therefore performs better in laminar
flow, because in laminar flow the thermal resistant is not limited to a thin region. The result
also shows twisted tape insert is more effective, if no pressure drop penalty is considered.
Twisted tape in turbulent flow is effective up to a certain Reynolds number range. It is also
concluded that twisted tape insert is not effective in turbulent flow, because it blocks the flow
and therefore pressure drop increases. Hence the thermo hydraulic performance of a twisted
tape is not good in turbulent flow. These conclusions are very useful for the application of
heat transfer enhancement in heat exchanger networks.
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Proc. of the 3'd International
Conference on Advances in Mechanical
SV National Institute of Technology,
Engineering, January 4-6, 2010
Surat - 395 007, Gujarat, India
References
[1] Anil Yadav,"Effect of half length twisted tape turbulator on heat transfer & pressure drop
characteristics inside a double pipe U-bend heat exchanger." Jordan journal of Mech. &
industrial engg. 2009, 3, 1, 17-22.
[2] S.Jaisankar, T.K.Radhakrishanan & K.N.Sheeba (2009), Experimental studies on heat
transfer & friction factor characteristics of forced circulation solar water heater system
fitted with helical twisted tapes, , Communicated by Associated Editor Brian Norton
[3] Zhi-min Un & Wang Bi "Convective heat transfer enhancement in a circular tube using
twisted tape." J. Heat Transfer, 2009,131, 8, 81-91
[4] P.Bharadwaj, A.D. Khondge, A.W.Date, "Heat transfer & pressure drop in spirally
grooved tube with twisted tape insert." J. Heat Transfer, 2009,52,5, 1938-1944.
[5] Paisarn Naphon , "Heat transfer & pressure drop in horizontal double pipes with &
without twisted tape inserts." International Communications in Heat and Mass Transfer,
2006,33,2,166-175.
[6] Ray, S. and Date, A. W. Friction and heat transfer characteristics of flow through
square duct with twisted tape insert. Int. J. Heat and Mass Transfer, 2003,46, 889--902.
[7] Suresh Kumar, P., Mahanta, P. and Dewan, "A Study of laminar flow in a large
diameter annulus with twisted tape inserts." In Proceedings of 2nd International
Conference on Heat Transfer, Fluid Mechanics, and Thermodynamics, Victoria Falls,
Zambia, 2003, paper KP3.
[8] Wang, L. and Sunden, B. "Performance comparison of some tube inserts." Int.
Communication. Heat Transfer, 2002, 29, 45--56.
[9] Saha, S. K. and Dutta "A Thermo-hydraulic study of laminar swirl flow through a
circular tube fitted with twisted tapes." Trans. ASME, J. Heat Transfer, 2001, 123,417421.
[10] Saha, S. K. and Bhunia, K. "Heat transfer and pressure drop characteristics of varying
pitch twisted-tape-generated laminar smooth swirl flow." In Proceedings of 4th ISHMTASME Heat and Mass Transfer Conference, India, 2000, 423-428.
[11] Saha, S. K., Dutta, A. and Dhal, S. K. "Friction and heat transfer characteristics of
laminar swirl flow through a circular tube fitted with regularly spaced twisted-tape
elements." Int. J. Heat and Mass Transfer, 2001, 44,4211-4223.
[12] Liao, Q. and Xin, M. D. "Augmentation of convective heat transfer inside tubes with
three-dimensional internal extended surfaces and twisted tape inserts." Chem. Eng. J.,
2000,78,95--105.
[13] S.Eiamsa-ard,
K.Wongcharee,
P.Eiamsa-ard,
c.Thianpong
"Heat
transfer
enhancement using delta winglet twisted tape inserts." Applied Thermal Engg. 2009,
30,4,310-3181,
[14] Smith Eiamsa-ard,Chinaruk thianpong, Peterpics Eiasmsa-ard & Pongjet omvonge
"Convective heat transfer in a circular tube with short length twisted tape." International
Communications in Heat & Mass Transfer.2009, 36,4, 363-371.
[15] S.Eiamsa-ard, K.Wongcharee, S.Shipattanapipat, "3_D Numerical simulation of swirl
flow & convective heat transfer in a circular tube induced by means of loose fit twisted
tapes." International Communications in Heat & Mass Transfer.2009, 36, 9, 947-955.
[16] K.V.Sharma,L.Syam Sunder, P.K. Sharma, "Estimation of heat transfer coefficient &
friction factor in transitation flow with low volume concentration of AI203 Nano fluid
flowing in a circular tube & with twisted tape." International Communications in Heat &
Mass Transfer.2009, 36, 5, 503-507.
[17] Hong,Xianhe Deng, Kuo Huang, &Zhiwo U, "Compound heat transfer enhancement of
a converging diverging tube with evenly spaced twisted tapes." Chinese Journal of
chemical Engg. 2007, 15,6,814-820.
[18] S.Eiamsa-ard, P.Eiamsa-ard, C.Thianpong, "Turbulent heat transfer enhancement by
counter/co-swirling flow in a tube fitted with twin twisted tape." Experimental thermal &
fluid science, 2009, 34, 1, 53-62.
[19] Liao, M.D.Xin, Augmentation of convective heat transfer inside tubes with 3-D internal
extended surfaces & twisted tape inserts. Chemical Engg. Journal. 2000,.78.2,95-105.
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