Experimental Analysis of Heat Transfer Augmentation in Double Pipe Heat Exchanger using Tangential Entry of Fluid

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1 ISR Journal of Mecanical & Civil Engineering (ISRJMCE) e-issn: ,p-ISSN: X PP Experimental Analysis of Heat Transfer Augmentation in Double Pipe Heat Excanger using Tangential Entry of Fluid Hanumant Jagdale, Subas Laane (Department of Mecanical Engineering, MIT Aurangabad, Dr. BAMU Aurangabad, Maarastra, India) Abstract:In tis work, te effect of eat transfer enancement of swirl generator wit tangential injection of fluid was examined. Te five tangential injectors are placed suc tat tey are equidistance along te lengt of pipe to improve te efficiency of eat transfer in concentric pipe eat excanger te injectors are designed and placed suc tat it creates tangential flow in te pipe. Te experiment performed for water as working fluid, ot water flowing troug inner tube of material mild steel wit inner diameter (ID) 16 mm and outer diameter (D) 21 mm and cold water flowing troug annulus space to generate swirling motion. Te outer tube of material UPVC (un-plasticized polyvinyl cloride) aving ID 35 mm and D 42 mm. Te experiment was performed for different Reynolds number ranging from for parallel and counter flow configurations. It is observed from te experimental results tat te eat transfer rate increased wit increase in Reynolds number. Heat transfer rate was increased about 20 % to 70 % wit tangential injector type swirl generator tan te eat excanger witout tangential injectors. It was also observed tat te maximum eat transfer coefficients (1613 W/ m2k) could be acieved at Reynolds number of 4600 for all (five) nozzles opening wit 70 % increase in eat transfer. Keywords - Tangential, swirl flow, eat transfer augmentation, nozzles I. INTRDUCTIN Heat transfer is widely used in many applications in eat excangers, cemical process, gas and oil production, air condition, automotive or food industries. Modern engineering and tecnology is moving constantly upward on te temperature scale and subsequently te concept of augmentation of eat transfer as derived te attention of many scientists and engineers in te past few decades [1]. A general consideration in designing a eat excanger is to make it compact, i.e., increase te overall eat transfer coefficient. Anoter consideration is reducing te temperature of driving forces wic enances te second law efficiency and decreases entropy generation. ver te past decades, several metods ave developed and extensively applied to eat excangers [2]. Te double pipe eat excangers are te most important device used in industrial and engineering applications. Te economic and energy considerations continuously motivate investigators to searc for efficient metods of eat transfer. Tere are different eat transfer augmentations metods available to increase te eat transfer rate and make instrument compact and incorporated into eat excanger are passive, active and compound tecniques [3]. Passive tecnique is used surface or geometrical modifications to te flow by incorporating inserts or additional devices. Higer eat transfer coefficients acieved by disturbing te flow beavior wic also leads to increase in te pressure drop. Passive tecniques old te advantage over te active tecniques as tey do not require any direct input of external power [3-4]. Tis tecnique includes treated surfaces, roug surfaces, extended fins, swirl flow device, coiled tubes etc. Active tecniques require external power to disturb te flow and improvement in eat transfer rate. Tis tecnique finds limited application because of te need of external power in many practical applications [4]. Tis tecnique includes mecanical aids, surface vibration, fluid vibration, injection, jet impingements etc. In compound tecniques, tere is use of one or more tan one of te above mentioned tecniques in combination to improve te performance of a eat excanger [4]. Active and compound metods are rarely used because of teir complexity & cost [5]. Te swirl flow is one of te tecniques tat ave been used successfully in te past to augment eat transfer [6]. Te eat transfer augmentation along wit swirl in te flow was proposed by Kreit and Margolis [7]. In tis concept, tangential injection was used and te vortex motion maintained by repeated addition of fluid troug appropriately spaced injection oles for any desired distance. Swirl flows result from an application of a spiral motion, a swirl velocity component (also called as tangential or azimutal velocity component) being imparted to te flow by te use of various swirl-generating metods. Many researcers ave studied te eat transfer caracteristics of swirl flows by using various swirls. Generally, te swirling pipe flows are classified into two types: (i) Continuous swirl flows, wic maintain teir caracteristics over entire lengt of test section; 5 t National Conference RDME 2016, t Marc Page

2 and (ii) decaying swirl flows [8]. Gupta et al. [9] classified te metod of generating swirl into tree main categories- (i) tangential entry, (ii) guide vanes and (iii) direct rotation. Te tangential entry of te fluid into a duct stream can be acieved by a single tangential inlet duct (circular or rectangular at different angles to te pipe axis) or more tan one tangential entry, tangential inlet nozzles, tangential macined slots and tangentially drilled slots. Te swirl can be produced in te flow by tangential of te fluid by single tangential entry or te combination of axial plus tangential entry. Dir, et al. [10] experimentally determined augmentation of eat transfer wit air as te test fluid and Reynolds numbers ranging from to Te air was injected tangential to te inner walls of te eat excanger tubes troug square edged injectors extending perpendicular from te tube surface. Te net augmentation of eat transfer, at constant pumping power, was between 3% and 14% depending on te momentum ratio. It was also found tat te effectiveness of te system is igly dependent on te ratio of te rates of tangential to total momentum fluxes. Te two measure mecanisms of augmentation are observed- i) ig maximum axial velocity near te wall produces iger eat flux from te wall, ii) ig turbulence level in te middle region of tube improves mixing and tus, te rate of eat transfer [11]. Cang and Dir [11] carried out an experimental study for te eat transfer augmentation for a turbulent flow wit tangentially injected swirl flows in vertical tubes. It was found tat te momentum flux ratio is te most effective parameter tat enances eat transfer wile Reynolds number affects it weakly and te effect of te fluid Prandtl number is very weak. Also, te injector tube diameter and number of injectors do not affect te eat transfer enancement. Te effect of injection include swirl flow on single and two pase eat transfer using water as a working fluid was investigated by Guo and Dir [6]. It was found tat, on a constant pumping power basis, a net enancement of about 20% could be acieved experimentally at a momentum flux ratio of about 9.6. Te different parameters of swirling flow generated by injection were studied experimentally by Akpinar et al. [12-13] and Çakmak and Yıldız [14]. Tey studied te effect of oles diameter, oles number and angle of injection on te eat transfer rate and pressure drop. Tey found tat, using injector to create swirling flow enances eat transfer rate but it increases te pressure drop and requires more pumping power. II. EXPERIMENTAL DETAILS Experiment was performed for bot parallel flow and counter flow for different values of Reynolds number from 2000 to 5000 and for different nozzles openings. In tis experiment ot water was passed troug inner tube, wile cold water passed troug annulus space between inner and outer tube. Hot water was acieved by gas geyser provided to te experimental setup as sown in Fig. 1. Fig.1. (a) Layout of experimental set-up, (b) Working set-up (c) 3-D view of tangential injection tube of double pipe eat excanger wit tangential entry. 5 t National Conference RDME 2016, t Marc Page

3 Te mass flow rate of ot water keeping as constant i.e.300 LPH and tat of cold water was varied from 300 LPH to 600 LPH in te step of 50 LPH and simultaneously temperature of inlet and outlet of ot and cold water were recorded. Temperatures of cold water and ot water inlet and outlet were measured wit te elp of termocouples. Five nozzles are fitted tangential to te axis of pipe equidistance along te lengt of tube suc tat tey are tangentially perpendicular to te lengt of pipe. Nozzles are opened (consecutive opening and closing) one by one and te temperatures at te inlet and outlet of cold and ot water are measured. Te layout of experimental setup and working setup of tangential entry nozzles are sown in Fig. 1. III. MATHEMATICAL CALCULATINS In concentric eat excanger te eat given by ot fluid is expressed by Equation 1 and it is te function of mass of ot fluid, specific eat and temperature difference. m C T T (1) p o i Te eat received by cold fluid is expressed by Equation 2 and it is te function of mass of cold fluid, specific eat and temperature difference. c m C T T (2) c p co ci Te average eat transfer rate for ot and cold fluid is calculated using Equation 3 by calculating te average of eat given by ot fluid and eat received by cold fluid. avg c (3) 2 Te overall eat transfer coefficients is calculated by using Equation 4 and it is te function of average eat transfer, logaritmic mean temperature difference (LMTD) and outer surface area. U avg (4) A LMTD Reynolds number can be calculated by using Equation 5 and wic is te function of inertial force to te viscous force. Re Vd (5) Te termo pysical properties of water wic is used to calculate Reynolds number is determined at mean temperature calculated using Equation 6. T avg IV. T i T (6) 2 RESULTS AND DISCUSSIN Te experimental value of eat transfer coefficient is determined by plotting Wilson cart [15-16]. Te Wilson cart is plotted for variation of 1/ (Re) 0.8 wit 1/ Uo as sown in Fig. 2. Te y intercept as k (fouling resistance) taken from te Wilson cart and eat transfer enancement is calculated by using Equation 7. 1 exp t U 1 k (7) 5 t National Conference RDME 2016, t Marc Page

4 Fig.2. Wilson plot Te experiment was performed for different Reynolds number for different nozzle openings and te results obtained for parallel and counter flow models for eat transfer coefficient are discussed in tis section. Heat transfer coefficient results for plain tube and tube wit tangential entry for parallel flow and counter flow model are obtained for range of Reynolds number from Te comparison of te plain pipe and pipe wit tangential wit different nozzle openings is sown in Fig. 3. It is seen tat expt increases wit increase in Reynolds number for bot te configurations. For plain pipe expt value is varies from W/m 2 K for range of Reynolds number As compared to tangential entry tube wit 1-nozzle and 2-nozzles opening plain tube is efficient and gives better results. 40 % more expt is observed over te 1-nozzle open and 26 % more expt is observed over 2-nozzle openings. For 3-nozzles opening, 4-nozzles openings and 5-nozzle openings value of expt dominates over te plain pipe. About 35 %, 72 % and 77 % augmentation in expt for 3-nozzles openings, 4-nozzles openings and 5- nozzle openings over te plain pipe configuration is acieved respectively. For parallel flow model consecutive tree openings of nozzles are required for te better results. Fig.3. Variation of eat transfer coefficient wit Reynolds number for plain tube and tangential injection wit different nozzles openings (Parallel flow model) Te comparison between plain pipe and tangential entry pipe wit different nozzle entries open for counter flow configuration as sown in Fig.4. It is seen tat expt increases wit increase in Re for bot te pipes. For plain pipe expt value is varies from W/m 2 K for range of Re from As compared to tangential entry pipe wit 1-nozzle openings and 2-nozzles openings, plain pipe configuration is efficient and 5 t National Conference RDME 2016, t Marc Page

5 gives better results. About 38 % more expt is observed over te 1-nozzle open and 25 % more expt is observed over 2-nozzle openings. For 3- nozzles, 4-nozzles and 5-nozzle openings value of expt dominates over te plain tube value. About 19%, 33 % and 67 % augmentation in expt for 3- nozzles, 4-nozzles and 5-nozzle openings over te plain tube is acieved respectively. For counter flow model consecutive tree openings of nozzles are required for te better results. As te number of entries increases expt increases wit increase in Reynolds number. Fig.4. Variation of eat transfer coefficient wit Reynolds number for plain tube and tangential injection wit different nozzles openings (Counter flow model) Fig.5. sows te performance of different tangential entries for parallel and counter flow model. From te experimental results reveals tat as te number of tangential entries increases eat transfer coefficient increases wit Reynolds number. It as been observed tat as te number of entries increases te eat transfer coefficient increases wit respect to te Reynolds number. Counter flow configuration gives te better results over te plain tube for all cases. As te number of entries increases te temperature difference goes on increasing along te flow ence te eat transfer coefficient also increases. Also te local turbulence gives te advantage of te mixing of fluid. Fig.5. Variation of eat transfer coefficient wit Reynolds number for tangential injection wit different nozzles openings (Parallel and counter flow model) 5 t National Conference RDME 2016, t Marc Page

6 V. CNCLUSINS Te experiment is performed for bot te plain tube and tube wit tangential injector entries and te conclusion is summarized as follows: As Reynolds number increases te eat transfer augmentation is increases for bot plain tube and tangential injection configurations. Te turbulence (swirl or vortex) in te flow is increased wit every addition of tangential entry nozzles. Te increase in eat transfer augmentation was observed about 70 % wit tangential entry configuration over plain pipe for counter flow configuration. Te igest eat transfer augmentation was found 1613 W/ m 2 K. Te best operating range of Reynolds number for tis experimentation is NMENCLATURES TNP tangential nozzles openings in parallel flow TNC tangential nozzles openings in counter flow LMTD log mean temperature difference LPH litres per our k fouling resistance REFERENCES [1] K Sailendra, A. Devi, n te enanced eat transfer in te oscillatory flow of liquid metals, Journal of Applied Fluid Mecanics, 4, 2011, [2] S Vaidifar, M Karom, Experimental study of eat transfer enancement in a eated tube caused by wire-coil and rings, Journal of Applied Fluid Mecanics, 8 (4), 2015, [3] N Kumar, P Murugesan, Review of twisted tapes eat transfer enancement, International Journal of Scientific and Engineering Researc, 3 (4), 2012, 1-9. [4] A Gupta, M Uniyal, Review of eat transfer augmentation troug different passive intensifier metod, ISR Journal of Mecanical and Civil Engineering, 1 (4), 2012, [5] S Babar, K Devade, Heat transfer enancement in pipe in pipe eat excanger wit swirling flow: Review, International Journal for Scientific Researc & Development, 3 (3), 2015, [6] Z Guo, V Dir, Single and two pase eat transfer in tangential injection-induced swirl flow, International Journal of Heat and Fluid Flow, 10 (3), 1989, [7] F. Kreit, D Margolis, Heat transfer and friction in turbulent vortex flow, Applied Scientific Researc, Section A, 8 (1), 1959, [8] M Yilmaz, Comakli, S Yapici, Enancement of eat transfer by turbulent decaying swirl flow, Energy Conversion and Management, 40 (13),1999, [9] A. K. Gupta, D. G. Lilley, N. Syred, Swirl Flows (Abacus Press, Cambridge, 1984). V Dir, S Monica, Heat transfer enancement using tangential injection, United State Patent, US A, [10] F Cang, V Dir, Mecanisms of eat transfer enancement and slow decay of swirl in tubes using tangential injection, International Journal of Heat and Fluid Flow, 16, 1995, [11] E Akpinar, Y Bicer, C Yildiz, D Pelivan, Heat transfer enancements in a concentric double pipe excanger equipped wit swirl elements, International Communications in Heat and Mass Transfer, 31 (6), 20014, [12] E Akpinar, Y Bicer, Investigation of eat transfer and exergy loss in a concentric double pipe excanger equipped wit swirl generator, International Journal of Termal Sciences, 44, 2005, [13] G Çakmak, C Yıldız, Te influence of te injectors wit swirling flow generating on te eat transfer in te concentric eat excanger, International Communications in Heat and Mass Transfer, 34, 2007, [14] M. Ratore, Engineering Heat and Mass Transfer, (3rd ed. New Deli: University science press, [15] J Rose, Heat-transfer coefficients, Wilson plots and accuracy of termal measurements, Experimental Termal and Fluid Science, 28, 2004, t National Conference RDME 2016, t Marc Page