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International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of …

International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.

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  • 1. Maughal Ahmed Ali Baig, Ibrahim Nouzil, Azzam Sheik, Ferraz Mohammed, Thameez /International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.1491-14961491 | P a g eHeat Transfer Augmentation in Concentric Tube Heat ExchangerUsing Twisted TapesMaughal Ahmed Ali Baig*, Ibrahim Nouzil**, Azzam Sheik**, FerrazMohammed**, Thameez***Associate Professor, Dept. of Mechanical Engg., Bearys Institute of technology, Mangalore, Karnataka, India.** Final Year Students, Dept. of Mechanical Engg., P. A. College of Engineering, Mangalore.ABSTRACTThe present paper deals with the results ofan experimental investigation carried out to findthe overall performance of suitably designedconcentric tube heat exchanger with passive heattransfer augmentation technique. The desiredaugmentation is attained with the help of twistedtape inserts. In addition to this, the performance oftwisted tapes with holes and with baffle plates iscarried out to find the suitable design for the heattransfer augmentation. The effect of twisted tapeinserts on effectiveness of heat exchanger isanalyzed at different mass flow rates. It is foundthat full length twisted tapes produce a betterperformance as compared to other designs tested.Keywords- Effectiveness, Heat exchangers, Inserts,Twisted TapesI. INTRODUCTIONEffective utilization of available energybecomes need of hour today. This obviously requireseffective devising. When it concerns heat energy thedevices are heat exchangers. Heat exchangers are usedin variety of applications. Some of the applications ofheat exchangers are in process industries, thermalPower plants, air-conditioning equipment’s,refrigerators, radiators for space vehicles, automobilesetc. Increase in Heat exchanger performance can leadto more economical design of heat exchanger whichcan help to make energy, material & cost savingsrelated to a heat exchange process. To increase thethermal performance of heat exchangers Heat transferaugmentation techniques are used. Heat transferaugmentation techniques refer to different methodsused to increase rate of heat transfer without affectingmuch the overall performance of the system. Thesetechniques broadly divided in two groups viz. passive,and active. Active techniques involves some externalpower input for the enhancement of heat transfer,some examples of active techniques include inducedvibrations in the setup, the use of a magnetic field todisturb the seeded light particles in a flowing streametc. Passive techniques generally use surface orgeometrical modifications to the flow channel byincorporating inserts or additional devices, forexample, use of inserts, use of rough surfaces etc.In present work passive technique of augmentation isused. The Concentric tube heat exchanger is fittedwith different types of twisted tapes and its effect isstudied.Passive heat transfer augmentation methods:Passive heat transfer augmentation methods as statedearlier does not need any external power input. In theconvective heat transfer one of the ways to enhanceheat transfer rate is to increase the effective surfacearea and repository time of the fluid in the effectiveregion. The passive methods are based on the sameprinciple. Use of this technique causes the swirl in thebulk of the fluids and disturbs the actual boundarylayer so as to increase effective surface area, residencetime and consequently heat transfer coefficient inexisting system. Following Methods are generallyused,1. Inserts2. Extended surface3. Surface modifications4. Use of additives.Inserts: Inserts refer to the additional arrangementsmade as an obstacle to fluid flow so as to augmentheat transfer. Different types of inserts are Twisted tapes and coils Ribs and baffles FinsIn the present study effect of different types of twistedtapes are studied.Twisted Tape:Twisted tapes are the metallic strips twisted withsome suitable techniques with desired shape anddimension, inserted in the flow. Following are themain categories of twisted tape which are analyzed inthis study:i. Full length twisted tape: These tapes havelength equal to length of test section.ii. Varying length twisted tape: These aredistinguished from first category with regardsthat they are not having the length equal to lengthof test section, but half length, ¾ th length, ¼thlength of section etc.iii. Regularly spaced twisted tapes: These are shortlength tapes of different pitches spaced byconnecting together.
  • 2. Maughal Ahmed Ali Baig, Ibrahim Nouzil, Azzam Sheik, Ferraz Mohammed, Thameez /International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.1491-14961492 | P a g eiv. Tape with attached baffles: Baffles are attachedto the twisted tape at some intervals so as toachieve more augmentation.v. Tapes with holes: Slots and holes of suitabledimensions made in the twisted tape so as tocreate more turbulence.Common attributes of tape:i. Width: Small width tapes are preferred tominimize pressure drop.ii. Thickness: Thickness of the tape playsimportant role in its fabrication and also hascontribution in fin effectiii. Pitch: It is the distance between twoconsecutive twists measured axially.iv. Twist ratio: It is the ratio of pitch of tape totape width. So, if width of the tapeconsidered as a constant (as found generally)twist ratio depends on pitch only. Under thiscondition if pitch is more it means lessnumber of turns.v. Fin effect: If the tape material is conductivethen during the flow some heat will beabsorbed by the tape material itself till itssaturation. This is simply the loss ofavailable heat energy.II. EXPERIMENTAL SET-UPFig1.1: Experimental setupFig1.2: Schematic Diagram of the setupFig1.1 shows the experimental setup used to conductthe experiments. It consists of double pipe heatexchanger consisting of a test section & a 3 KW 3Lit,electric geyser to supply constant hot water & thecontrol system. The test section is a smooth stainlesssteel as an inner tube; and an outer mild steel pipe.The outer pipe is well insulated using glass wool heldwith jute rope to reduce heat losses to the atmosphere.Tap water is sent to geyser and then the heated wateris directed to the inner tube through a control valve.Three temperature measuring devices to measure theinlet& outlet temperature of hot water & outlet of coldwater. The inlet temperature of cold water ismeasured using mercury thermometer.Specifications:Inner diameter = 12.7mmInner pipe material = Stainless SteelOuter diameter = 38.1mmOuter pipe material = Mild SteelEffective length = 1175mmInner Twisted Tape:The table below shows the actual view of thetwisted tapes used. Three tapes with stainless steelmaterial are prepared with different attributes.Width, Length and pitch for all Tapes are keptsame, i.e. width=3 mm, length=1000 mm andpitch=60 mm.
  • 3. Maughal Ahmed Ali Baig, Ibrahim Nouzil, Azzam Sheik, Ferraz Mohammed, Thameez /International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.1491-14961493 | P a g eDetails of tape used in the present experiment:Tape I FulllengthtapeTapeIITapewithholesTapeIIITapewithbafflesIII. EXPERIMENTATIONA series of experimentation is carried outwith the heat exchanger set-up. Initially theexperiment is conducted without utilizing any heattransfer augmentation method (case I). Case I is set asbenchmark for the analysis of other augmentationmethods. The flow rate for both hot and cold water isvaried between 200cc/min to 800cc/min, consideringthe capacity of the electric geyser used, and at a timeboth the mass flow rates are kept almost constant.Four temperatures (cold water inlet and outlet, hotwater inlet and outlet) are measured with the digitaltemperature indicator. The mass flow rate is measuredmanually with help of measuring jar and stopwatch.The same procedure is repeated for all cases asfollowingi) Case II: Experimentation on Heat exchangerset up with full length twisted tape.ii) Case III: Experimentation on Heat exchangerset up with twisted tape with drilled holes.iii) Case IV: Experimentation on Heat exchangerset up with twisted tape with attached baffles.Process Variables:Inlet temperature of Cold water = TciOutlet temperature of cold water = Tcoinlet temperature of hot water = ThiOutlet temperature of hot water = ThoCold water mass flow rate = McHot water mass flow rate = MhFormulae Used:Heat transfer from hot waterQh = mh Cph (Thi-Tho)Heat Transfer from cold waterQc = mc Cpc (Tco-Tci)LMTD= (Θ2-Θ1)/ ln (Θ2/Θ1)Θ1=Tho-Tci Θ2=Thi-TcoOverall heat transfer co-efficientU = Q/(A*LMTD)Effectiveness E = (Thi-Tho)/ (Thi-Tci)IV. RESULT AND DISCUSSIONS:Experimentation is performed with all fourcases mentioned earlier. Effectiveness, Overall heattransfer coefficient and LMTD calculated for allconditions. Parameters plotted for different values ofmass flow rate.Case I: Without any augmentationtechniqueFig1.3: Effectiveness vs. Mass flow rate for case IFrom the fig1.3 it is clear that as the flowrate increases the effectiveness decreases. This is dueto the increase in velocity of the working fluid whichreduces the repository time of the fluid in the effectiveregion of the heat exchanger.00.10.20.30.40.50.60 200 400 600 800effectivenessMass flow rateEffectiveness vs Mass flow rate
  • 4. Maughal Ahmed Ali Baig, Ibrahim Nouzil, Azzam Sheik, Ferraz Mohammed, Thameez /International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.1491-14961494 | P a g eFig1.4: LMTD vs. Mass flow Rate for case IFig1.5: Overall heat transfer coefficient vs. mass flowrate for case IFrom fig1.5, as the flow rate increases the turbulenceinduced in flow also increases. Therefore the overall heattransfer coefficient also increases.Case II: With Twisted TapeFig2.1: Effectiveness vs. mass flow ratefor case IIFig2.2: Overall heat transfer coefficientvs. mass flow rate for case IIFig2.3: LMTD vs. Mass flow rate for caseIIFrom fig 2.1 and fig 2.2 it is clear that theeffectiveness and overall heat transfer coefficientincrease when twisted tape is inserted into the innerpipe. The twisted tape induces swirling motion in thewater, thereby increasing the repository time of thefluid in the effective region and as a result heattransfer increases.Case III: For Twisted Tape with Holes051015202530350 200 400 600 800LMTDmass flow rate (cc/min)Mass flow rate vs LMTD01002003004005006007000 200 400 600 800overallheattransfercoeffecient(W/m2K)mass flow rate (cc/min)Overall heat transfer coeffecientvs Mass flow rate00.10.20.30.40.50.60.70 200 400 600 800effectivenessmass flow rateEffectiveness vs mass flow rate020040060080010000 200 400 600 800overallheattransfercoeffecient(W/m2K)mass flow rate (cc/min)overall heat transfer coeffecientVs mass flow rate051015202530350 200 400 600 800LMTDmass flow rate (cc/min)LMTD vs Mass Flow Rate
  • 5. Maughal Ahmed Ali Baig, Ibrahim Nouzil, Azzam Sheik, Ferraz Mohammed, Thameez /International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.1491-14961495 | P a g eFig3.1: effectiveness vs. mass flow rate for case IIIFig3.2: overall heat transfer coefficient vs. mass flowrate for case IIIFig3.3: LMTD vs. Mass flow rate for caseIIIFrom the fig 3.1 and fig 3.2 for twisted tape withholes the effectiveness is better than the benchmark.But compared to case II the effectiveness is lower.This may be due to discontinuous swirl motion ofthe fluid.Case IV: Twisted Tape with BafflesFig4.1: Effectiveness vs. mass flow rate for caseIVFig4.2: overall heat transfer coefficient vs. massflow rate for case IV00.10.20.30.40.50.60.70 200 400 600 800effectivenessmass flow rate (cc/min)Effectiveness vs Mass flow rate020040060080010000 200 400 600 800overallheattransfercoeffecient(W/m2K)mass flow rate (cc/min)overall heat transfer coeffecientvs mass flow rate0510152025300 200 400 600 800LMTDmass flow rate (cc/min)LMTD vs Mass flow rate00.10.20.30.40.50.60 200 400 600 800effectiveness mass flow rate (cc/min)Effectiveness vs Mass flow rate020040060080010000 200 400 600 800overallheattransfercoeffecient(W/m2K)mass flow rate (cc/min)overall heat transfer coeffecientVs mass flow rate
  • 6. Maughal Ahmed Ali Baig, Ibrahim Nouzil, Azzam Sheik, Ferraz Mohammed, Thameez /International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.1491-14961496 | P a g eFig4.2: LMTD vs. Mass flow rateFrom fig4.1 and fig4.2 it is observed that there issubstantial increase in effectiveness for increasedmass flow rate. The result may be further enhanced byattaching more number of baffles in the twisted tape.Comparison of different techniquesV. CONCLUSIONSExperimental investigations have beencarried out to study the effects of tape inserts on theperformance of concentric tube heat exchanger.Effectiveness, overall heat transfer coefficient andLMTD are analyzed using mentioned heat transferaugmentation methods. From the graphs plotted thefollowing conclusions are made1. The heat transfer in the heat exchanger could beenhanced by using Tapes.2. The full length twisted tape increases heattransfer by a percentage of 8.9%.3. Twisted tape with holes and baffles of presentconfiguration underperform compared to fulltwisted tape.REFERENCES[1] S.K.Saha A.Dutta “ Thermo hydraulic studyof laminar swirl flow through a circular tubefitted with twisted tapes” Trans. ASMEJournal of heat transfer June 2001, Vol-123/pages 417-427.[2] Zhi-Min Lin, Liang-Bi Wang “Convectiveheat transfer enhancement in a circular tubeusing twisted tape” Trans ASME journal ofheat transfer Aug 2009,Vol- 131/081901-1-12.[3] Watcharin Noothong, Smith Eiamsa-ard andPongjet Promvonge” Effect of twisted tapeinserts on heat transfer in tube” 2nd jointinternational conference on “sustainableEnergy and Environment 2006” Bangkok,Thiland.[4] Paisarn Naphon “Heat transfer and pressuredrop in the horizontal double pipes with andwithout twisted tape in-sert” 2005 ElsevierLtd.[5] Smith Eiamsa-ard , Chinaruk Thianpong,Pongjet Promvonge “ Experimentalinvestigation of heat transfer and flow frictionin a Circular tube fitted with regularly spacedtwisted tape elements” InternationalCommunications in Heat and Mass TransferVol. 33, Dec 2006.[6] Ashis K. Mazumder, Sujoy K. Saha“Enhancement of Thermo hydraulicPerformance of Turbulent Flow in Rec-tangular and Square Ribbed Ducts WithTwisted-Tape Inserts” Journal of HeatTransfer AUGUST 2008, Vol. 130.[7] A Dewan1 , P Mahanta1, K Sumithra Raju1and P Suresh Kumar “Review of passive heattransfer augmentation techniques” Proc. InstnMech. Engrs Vol. 218.051015202530350 200 400 600 800LMTDmass flow rate (cc/min)LMTD vs Mass flow rate00.20.40.60.8200 400 600 800EffectivenessMass flow rate (cc/min)Effectiveness vs Mass flow rateEffectiveness basic Effectiveness holesEffectiveness twisted effectiveness baffles

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