EFFECT OF PITCH NUMBER IN OVERALL HEAT TRANSFER RATE IN DOUBLE PIPE HELICAL HEAT EXCHANGER

Transcription

1 Volume 116 No , 1-6 ISSN: (printed version); ISSN: (on-line version) url: ijpam.eu EFFECT OF PITCH NUMBER IN OVERALL HEAT TRANSFER RATE IN DOUBLE PIPE HELICAL HEAT EXCHANGER T.Kanthimathi 1, Naga Sai Ram.Gopisetti 2, Bharamara 3, PRishyank.Ch 4 1 Assistant Professor, Department of Mehanial Engineering, K L University, India 2 Under Graduate, Department of Mehanial Engineering, K L University, India 2 sairam27@hotmail.om 3 Assoiate Professor, Mehanial Engineering, JNTU Collage of Engineerign,India Abstrat: The aim of the following researh to study the tube in tube helial oil heat exhanger where with inrease in the pith will inrease the overall heat transfer rate. Sine that tube in tube, helial oil often taken small area and the height of the tube in tube helial oil heat exhanger an be onfigured by the relation index proposed in the following paper. The heat transfer rate in the heat exhanger depended on the heat transfer oeffiient, surfae area and temperature differene. Geometry of the heat transfer area and the turbulene fator plays a major role in the enhanement of the heat transfer rate, In this paper numerial analysis of a tube in tube helial oil heat exhanger is done using Ansys Fluent as a ounter flow arrangement. The pith of the helial tube is varied for the onstant length of the oil and the overall heat transfer rate is alulated. Results have shown that as the pith is redued the heat transfer rate is inreased. Keywords: Pith number, Helial oil heat exhanger, Overall Heat Transfer. 1. Introdution Heat exhanger is the devie that helps to transfer heat from the hot body to old body. There are many types of the heat exhanger available based upon the TEMA. There is some rare type of the heat hanger available like double pass and tube in tube helial oil heat exhanger, whih omes to tubular type of heat exhanger. The tube in tube helial oil type of heat exhanger offers a wide option for the design in whih liquid to liquid heat transfer an be inorporated along with the refrigerant to liquid and implementation of Nano fluids an be applied. The steep urvature s in the tubes introdues the seondary flow that is normal to the primary flow, whih leads to form the transitionflow, with the turbulent onditions inreases the heat transfer.assuh, number of turns, whih is responsible for the inrease in the urvatures that indued in inrease in the Dean Number, whih is assoiated by the heat transfer with the urvature s, with inrease in the Dean Number the inrease in the Turbulene is aused by urvature whih is diretly depended on the pith of the helial oil. Whih is modeled as the k-e model, So any flutuations in the pith index will show immense effet on the Overall heat exhange value. The implementation s and usage of double pipe helial tube heat exhangers is in the reovery of CO 2, ooling the hydroarbons and in polymer industries for ooling, sine they are ompat in nature they an be used in the spae limitation plaes like spae and steam generation and marine and industrial appliation. Extensive usage of this type of exhangers are used in low temperature ryogeni researh. 2. Literature Review The experimental omparison between tube in tube and helial oil heat exhangers have been made by the Ruhal G.Humbare,Suraj R.Gurav et al 2015[1]. The analysis of helial oil heat exhanger is done by Amol Andhare and V.M Kriplani et al 2014 [2] orrelations were proposed to alulate shell side and tube side heat transfer oeffiients for different urvature ratios and pith ratios. Wale l.a.aly et al 2014[3]has performed CFD study to investigate the 3-D turbulene flow and heat transfer of oiled tube in tube heat exhangers results shown that Gnielinski orrelation was used extensively for prediting nusselt number as the funtion of prandtl number and the onvetive o-effiients in inner oil tube and annular oil tube. J.S Jaykumar S.M Mahajani et al 2008[4] have performed CFD simulations for vertial and horizontal oriented 1

2 helial oils by varying pith irle diameter and tube pith and pipe diameter and study the influene on heat transfer by varying this parameter a orrelation was presented to predit the loal values of nussult number as the funtion of angular loation of the point. Timothy J.Rennie et al 2006[5]has performed the experimental study on the tube in tube helial oil heat exhanger by varying flow rates within the turbulent region in inner tube and in the annulus results have shown that the experimental data fit well with the numerial values for larger heat exhangers but some differenes between numerial and experimental data for smaller oil. 3. Methodology From the overall heat transfer rate, it is proven that the area is the possible terms in adjusting the parameter where the pith ome into play a possible hange. To prove the pith is the possible parameter for the heat transfer rate the following derivation has been made. The following are the notation taken for the derivation L is the length of the helial oil. =1.5 m N is the number of turns of the oil. R is the base radius if the helial oil. =0.15m p is the pith of the helial oil. Q avg is the average heat transfer rate. U is the overall heat transfer rate. d o-i is the annulus thikness. t is the orreted log mean temperature differene. A Q = U t Qavg U = A t Q Eq. (2) Eq. (3) avg U = Eq. (4) U π d L t o i Q avg = Eq. (5) 2 2 π do i N (2 π R) + p t 1 U = f p Eq. (6) 1 Uα Eq. (7) p From the eq 7 it is proved that the hange in the heat transfer rate has the effet by the hange in the pith if the spiral. For inrease in the heat transfer take plae for derease in the pith and for the pith it annot be zero and annot be equal to length of the helial oil. Sine the study was not on the overall design of the tube in tube helial oil heat exhanger but speified to the pith of it so the numerial simulation was made by varying the pith in two ases by 0.09m and 0.20 m. the type of flow made was ounter flow type. In order to verify the above equation numerial simulation was made on the Anysys Fluent tool where the solver used was k-ε type and with the turbulent intensity of 5% and Hydrauli length as 10mwith boundary onditions of fluid as follows. Figure 1. The design nomenlature of the Double pipe helial oil heat exhanger π 2 2 L = N (2 R) + p Eq. (1) 2

3 Figure 2. boundary onditions of the numerial simulation of the double pipe helial heat exhanger outlet and C is the hot waterinlet and D is the hot water outlet. Figure 5.showing the outlet and inlet temperatures of the tube in tube helial oil heat exhangers of Figure 3. the different mesh modelsof tube in tube helial oil heat exhangers A is of pith m B is of pith 0.07 m C is of pith 0.09m. The mesh that was generated within ANSYS and automati mesh with the refinement of 2 at the inlet and outlets faes and by making sure that the mesh has aptured the steepurvature of the geometry. The type of assembly method was ut ell method and an inflation layers are of 5 is added in order to aount the heat transfer in at the wall. pith 0.07 A is old water inlet B is the old water outlet and C is the hot water inlet and D is the hot water outlet 4. Results The Computational results that has been observed after the solution is made to onverged pith 0.09 A is old water inlet B is the old water outlet and C is the hot water inlet and D is the hot water outlet. Figure 7. showing the various heat transfer Initializationand propagation in tube in tube helial oil heat exhangers Figure 4. showing the outlet and inlet temperatures of the tube in tube helial oil heat ex-hangers of pith 0.09 A is old water inlet B is the old water 3

4 It is noted form the figures 4,5,6 of B images the inner layers of the old outlet have shown the derease of temperature layers and has given maximum derease in the pith of 0.045m tube double pipe helial oil heat exhanger. Form the above figure7 it is observed that the derease in the pith has shown that heat transfer rate has started in advane for the outlet pipe than that of greater pith. Results show that pith of helial oil heat exhanger has a greater effet on the over- all heat transfer oeffiient so the effet of Pith on the overall heat transfer oeffiients. The following are the equation taken for the alulation of the overall heat transfer oeffiients. Q = m& ( T T ) Eq. (8) old i o Q = m& ( T T ) Eq. (9) Q hot h h hi ho avg Qold + Qhot = Eq. (10) Aannular = π dout in N (2 π R) + p Eq. (11) ( Thi To ) ( Thi Ti ) LMTD = Eq. (12) ( Thi To ) ln ( Thi Ti ) U Qavg = Eq. (13) A LMTD t annular Corretion fator of the ounter flow is 0.9. From the equation (11) and from equation (13) the overall heat transfer rate is given in the equation (13) so equation (7) argues best with equation (13) hene provide an proof of justifiation of problem statement 4. Conlusion The graph is fitted to a ubi equation for the approximation equation in terms of terms of pith of the helial oil heat exhanger and the overall heat transfer rate of the heat exhanger. Figure 8. showing the graph of the pith variation and over all heat transfer oeffiient of tube in tube helial oil heat exhanger U = p p Eq.(14) It is observed form the above equation if the pith equals to the length of the helial oil there is no heat transfer and above orrelation is to used only within the range of m to 0.09 m of the pith. With respetive to the simulation results from the figure 4 of B it is observed that the heating gradient along the fae has no proper formation and from the figure 5 of B the generation of the heat gradient form the annulus fae has visual hange with the area showing the least default value as 27 0 C and for the next 6 of B also show an higher heating gradient.this numerial results prove that the with inrease in the pith there is an notieable hange in heat exhanging pattern in the working media. With respetive to the figure 8 it is observed that the ooling url of the outer tube also shows the proportional pattern as the variation of pith where inrease in the pith the length of the ooling url of the hot fluid has given an onlusion the inorporating the lower pith helps in the ooling of the hot fluid well in advane rather than the just ooling in that instant this intern helps in the reservoir mehanism of ooling and even helps in designing the ompat heat exhangers. It is proved from the numerial analysis pith shows the parametri hange in the number of turns where there is hange in the dean number of the geometry, whih effeted the overall heat transfer oeffiient. While designing the tube in tube helial oil heat exhanger the pith of it should be in relation that have values proved from the study rather than designing with relation to the radius of the helial oil. Referenes [1]Amol Andhat and V.M Kriplani 2014 Thermal Analysis of a Helial Coil Heat Exhanger International Journal of Innovative Researh in Advaned Engineering (IJIRAE) Volume 1 Pg No [2]Aly, Wael IA "Computational Fluid Dynamis and Optimization of Flow and Heat Transfer in Coiled Tube-in-Tube Heat Exhangers Under Turbulent Flow Conditions." Journal of 4

5 Thermal Siene and Engineering Appliations 6.3 Volume 79 Pg No [3] A.P. Vetrivel, S.Senthilkumaren, G. Sakthinathan, R.Anandhan, Review for The Heat Transfer Enhanement of Heat Exhanger Using Nanofluids, Volume 1 Pg No [4]Jayakumar, J. S "Experimental and CFD estimation of heat transfer in helially oiled heat exhangers."chemial engineering researh and Design 86,Pg No [5]Rennie, Timothy J., and Vijaya GS Raghavan Numerial studies of a double-pipe helial heat exhanger." Applied Thermal Engineering Pg No [6]Ruhal G.Humbare, Suraj R.Gurav Analysis of Heat Transfer Enhanement in Tubein-tube Helial Coil Heat Exhangers International Journal of Advaned Engineering and Tehnology.5.1 Volume 1 Pg No

6 6