CFD Analysis and Optimization of Heat Transfer in Double Pipe Heat Exchanger with Helical-Tap Inserts at Annulus of Inner Pipe

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1 IOR Journal Mecanical and Civil Engineering (IOR-JMCE) e-in: ,p-IN: X, Volume 13, Issue 3 Ver. VII (May- Jun. 2016), PP CFD Analysis and Optimization Heat Transfer in Double Pipe Heat Excanger wit Helical-Tap Inserts at Annulus Inner Pipe 1 Barat Busan Verma, 2 aurab Kumar 1 ME tudent, 2 Associate Pr., Mecanical Department, Raipur Institutes Tecnology, Raipur, India Abstract: In excanger for increasing te rate wit elical-tape inserts ave useful. Generally, elicaltape inserts causes swirl flow introduces at outside inner tube wic continuously disrupts te termal boundary layer on te tube. Tis analysis as done on a single unit pipe excanger tose are used in a excanger and tis investigation is useful to increase te termal caracteristics a excanger. To analyze te caracteristics elical-tap inserts at inner pipe, a 3-D analytical model as been developed. From te analysis it is cleared tat tere are good relation between no. and friction for enancing te. T k-ω turbulent model is to be selected for simulation because it gives better turbulent model. From analysis, elical-tape inserts increase te rate wit expectation pressure drop. In tis work an analysis as been done on penomenon elical-tap inserts at te inner pipe. Keywords: Double pipe excanger, Heat augmentation tecniques, Helical-tape insert, Pitc lengt, Numerical investigation, Computational dynamics, Turbulence modeling,, number. I. Introduction Te procedure designing te excanger is difficult, because it required correct analysis rate, flow rate, drop in pressure and oter calculation tat give te result for long term establised and economically preference te equipment. Te callenge is to designing a excanger for better performance and makes it to compact to gain a more. Normally a excanger used in power plants, cemical plants, AC equipments, Freezer and oter plants wic provide or remove from different types. Tis involves uge investments annually for bot operation and capital costs. It is required to reduce te overall dimensions and caracteristics excanger. Te need to analyze and optimize te excanger to conserved and developed it. Heat excanger wit elical-tap inserts at inner pipe, from te velocity vector, it is observed tat te flow water in plain tube is straigt line but in case elical-tap flow is swirl, swirl flow in tube causes te surface area effected in increases, tereby rate increases but pressure drop also increases because flow abstraction. Tis pressure drops varies along wit no. on elical-tap. To predict te performance excanger is relating to te governing parameters suc as surface area for ring overall and temperature difference. Assuming tere is no to te surrounding and negligible KE and PE. m - mass ot entering (kg), m c - mass cold entering (kg), C - p. ot entering (J/kg K),C c p. cold entering (J/kg K), t 1 - temperature ot entering (K), t c1 - temperature cold entering (K), t 2 - temperature ot exit (K), t c2 - temperature cold exit (K), d - ydraulic diameter. Heat rejected by ot Q = m C (t 1 t 2 ) (1.1) Heat absorbed by cold Q c = m c C c (t c1 t c2 ) (1.2) Heat excange by two s Q = UAθ m (1.3) Were, U- Overall, A- Effective area, θ m - appropriate means temperature difference across excanger. As tere is variation in temperature difference ot and cold s point to point, so tat by te concept mean temperature difference te term ϴ m as introduced wic is appropriate mean temperature difference across excanger or known as log mean temperature difference. For parallel flow log mean temperature difference is given by θm = θ2 θ1 In( θ2 (1.4) θ1 ) For counter flow log mean temperature difference is given by θm = θ1 θ2 In( θ1 (1.5) θ2 ) Were, θ 1 = t 1 - t c1, θ 2 = t 2 - t c2 Of te many enancement tecniques tat can be employed, swirl flow generation by means full-lengt elicaltape inserts is found to be extremely effective [1], [2]. ignificant improvement can be obtained, particularly in laminar flows. Oter examples tecniques tat promote swirl flows include curved ducts, tangential injection, and twisted or convoluted ducts. Teir termal-ydraulic caracteristics, improvement potential, and typical applications ave been outlined. Helical-tap we know tat te is increase considerably for flow is well mixed and stirred. Because tis principle development for equipment to enancement tecnique excanger elical-tap inserts are used at inner pipe. DOI: / Page

2 CFD Analysis and Optimization Heat Transfer in Double Pipe Heat Excanger wit Helical-Tap.. Heat increase because : a. Tap reduce te ydraulic diameter, cause affect and enance te. b. Te elical-tap causes a tangential velocity component ence speed flow is increase near te wall surface. c. Tere may be from te tape. Figure 1: CFD model elical tape at inner pipe Figure 1.1 sown elical-tap, is described by te elical twisting nature tap providing te longer flow region or greater time for ring, te elical force for bulk flow are forcing for generation a secondary circulation because well mixed swirl flow increase te convective [5]. Te swirl flow wic is in fully developed nature, performance elical-tap and functional relation are given as below f = Re, y, δ/d (1.6) Nu = Re, y, δ/d, Pr (1.7) Based on a fundamental balance between inertia, viscous, and tape-geometry elical curvature induced forces, it is proposed tat tape-induced swirl flows can be scaled by a swirl parameter defined as [1] w = Re/ y (1.8) Were, te swirl number is based on te swirl velocity, and Re s = ρv s d/μ (1.9) II. Numerical Investigation Of Heat Excanger Wit Helical Tape Inserts At Annulus Of Inner Pipe For analysis our work te input data and boundary condition will be taken in [1] wic is experimentally investigate te penomenon. Table I Input data for double pipe excanger Lengt tube Inner diameter inner pipe, d i Outer diameter inner pipe, d o Inner diameter outer pipe, D i Outer diameter outer pipe, d o Material pipe Inner pipe Annulus 2.2 m m m m m Copper Cold water(300k) Hot water(353k) Table II Properties water Density, ρ kg/m 3 pecific Heat Capacity, C p Termal Conductivity, k Viscosity, µ 4182 J/kg K 0.6 W/m K kg/m s Table III Boundary condition for inner Inlet condition Outlet condition Inlet Temperature Inlet (0.376 m/s) Pressure Outlet 300 K Table IV Boundary condition for Inlet condition Inlet (Varies from to m/s) Outlet condition Pressure Outlet Inlet Temperature 353 III. Data Reduction Equations Te area weigted average temperature and static pressure were noted at te inlet and outlet surfaces te pipe. After setting all te above mentioned parameters simulation as been done and after simulation Coefficients for all te mentioned or considered Number ave been calculated as per te following relation and verified wit te findings Patnala sankra Rao [1]. Te correlation for te Calculation Factor (f) Colburn s Equation [1] is: f = 0.046(R 0.2 L ) (4.1) DOI: / Page

3 CFD Analysis and Optimization Heat Transfer in Double Pipe Heat Excanger wit Helical-Tap.. is: = ρvd... (4.2) µ Heat rate is given by: Q 1 = m C P (T co T ci )... (4.3) Q 2 = m C P T i T o.. (4.4) Q Avg = Q 1+Q (4.5) 2 Area: A = π d L..... (4.6) LMTD is given by: LMTD = T i T co (T o T ci ).. (4.7) ln( T i T co T o T ci ) is: Q =... (4.8) A LMTD is given by: = d... (4.9) k IV. Result And Discussion Te analysis excanger is done by te using different pitc lengt 50, 100, 150, 200 and 250 mm for 40 design points. Tis analysis is for ot water at velocity range to m/s and for cold water at constant velocity m/s. Te inlet temperature cold water and ot water is respectively 300 K and 353 K [1]. Figure 2: CFD Model for excanger wit elical tap different pitc lengt inserts. Figure 3: Inlet velocity ot domin Figure 4: Inlet velocity cold domin DOI: / Page

4 CFD Analysis and Optimization Heat Transfer in Double Pipe Heat Excanger wit Helical-Tap.. Figure 5: outlet temperature ot water Figure 6: outlet temperature cold water Figure 7: Mesed view elical tape Figure 8: Factor Vs wit elical tape Figure 9: Grap represents Vs wit different pitc lengt DOI: / Page

5 Heat, CFD Analysis and Optimization Heat Transfer in Double Pipe Heat Excanger wit Helical-Tap Pitc lengt, mm Figure 10: Grap represents optimum value pitc lengt It is cleared from te above result and rate are increases wit decrease te pitc lengt. Te above result is performed for te different pitc lengt and plot te comparison and Number and and. It is cleared tat te decrease wit increase in Number and increase wit Increase in Number. From te above result is also optimizing te elical tape pitc lengt for different velocity. Te maximum acieved at minimum pitc lengt wic is 50 mm and maximum velocity m/s. Te present researc also predicts tat by increasing te mass flow rate s, tere is miner variation in rate. V. Conclusion It is clear tat insertion a elical tape in a plain tube increase te termal performance te tube and furtermore if te pitc lengt elical tape is reduce increase in surface it increases te tube s termal performance more. Area Weigted te s temperature at te outlet te tube as been increased due to te insertion a elical tape in te tube. Te reason for te increment tese parameters is tat, due to te insertion a elical tape a swirl flow is created in te pipe wic elps te to take more and more from te tube wall. o it may be concluded tat, modifications sould be done in suc a way so tat average temperature as well as flux bot increases. To do tis, optimization procedure may be adopted to optimize different parameters to acieve te desired goal. cope for future work: Furter detailed studies can be carried out in tis area eiter troug experiments or wit te aid stware. number and friction values can be obtained for elical tap wit te same pitc at different velocity and similarly for elical tap wit te same velocity and different pitc in order to study te effect elical tap pitc lengt on number and friction. ome oter inserts may be used and similar investigations can be done and te values compared to tose elical tap inserts. References [1]. Patnala ankara Rao, K Kiran Kumar(2014), Numerical and Experimental Investigation Heat Transfer Augmentation in Double Pipe Heat Excanger wit Helical and Twisted Tape Inserts, Volume-4. [2]. K.ivakumar, K.Rajan( ) Performance Analysis Heat Transfer and Effectiveness on Laminar Flow wit Effect Various Flow Rates, Volume-7. [3]. Amarjit ing and atbir. egal (2013), Termoydraulic Analysis ell-and-tube Heat Excanger wit egmental Baffles. [4]. Kamles R. Raut, Pr. H.. Farkade (2014), Heat Transfer Enancement in Tube Using Insert A Review, Volume-2. [5]. Pr. Nares B. Damane, Pr. Matew V. Karvinkoppa, Pr. Murtuza. Dolkwala (2012), Heat Transfer Analysis Helical trip Insert wit Regularly paced Cut ections Placed Inside a Circular Pipe, Volume-2. [6]. Neeraj kumar Nagayac, Dr. Alka Bani Agrawal (2012), Review Heat Transfer Augmentation in Circular and Non-Circular Tube, Volume-2. [7]. Pr. P. B. Deankar, Pr. N.. Patil (2014), Heat Transfer Augmentation - A Review for Helical Tape Insert, Volume-3. [8]. K.ivakumar, K. Rajan,. Murali,. Prakas, V. Tanigaive, T. uryakumar (2015), Experimental Investigation Twisted Tape Insert on Laminar Flow Wit Uniform Heat Flux For Enancement Of Heat Transfer. [9]. P. B. Malwadkar, Lalit Pawar Pratik atav (2014), Experimental Investigation Heat Transfer Performance Matrix Coil Wire Inserts using CFD, Volume-1. [10]. Dr. D.. Kumar Heat and Mass Transfer.. K. Kataria and ons. 7 t Edition. Capter no. 14, pp Appendix Table V Numerical result at 50mm pitc F DOI: / Page

6 CFD Analysis and Optimization Heat Transfer in Double Pipe Heat Excanger wit Helical-Tap.. Table VI Numerical result at 100mm pitc f Table VII Numerical result at 150mm pitc F Table VIII Numerical result at 200mm pitc f Table IX Numerical result at 250mm pitc f DOI: / Page