Numerical Study of Heat Transfer Enhancement in Shell And Tube Heat Exchanger Using CFD

Numerical Study of Heat Transfer Enhancement in Shell And Tube Heat Exchanger Using CFD

Santosh K. Hulloli VSM Inst. Of Tech.

Nipani 591237 Karnataka State

Abstract

This paper numerically demonstrates the advantage of using different designs of baffles and semicircular turbulators inserted in the shell and tube heat exchangers. In this work, a shell and tube heat exchanger is considered for heat transfer enhancement studies. This heat exchanger uses kerosene on the shell side and crude oil on the tube side. The heat exchanger is designed using standard design procedure. CFD analysis is carried out for with baffles and without turbulators in the first stage. The design is incorporated with different designs of baffles and semicircular turbulators, and to study the heat transfer enhancement and pressure drop due to the baffles and turbulators is studied by Computational Fluid Dynamics (CFD) analysis in the second stage. And finally the pressure drop, outlet temperatures and heat transfer coefficient are validated against the theoretical results.

Introduction

The purpose of this present study is to predict the heat transfer coefficient, pressure drop and increased outlet temperatures of cold fluid on tube side and decreased temperatures of hot fluid on shell side, and also analysis is carried out for heat transfer coefficient, pressure drop and temperature variation for with inserting the different designs of baffles and semicircular turbulators and without inserting the baffles and semicircular turbulators.

The results are obtained for the five models (cases), first case is inserting only the segmental baffles on the shell side which is the base line results for the validation with the theoretical results.In the second case there are no baffles and turbulators in either shell or tube side i.e. plain shell and plain tube analysis is carried out for the heat exchanger model. In the third case inserting the segmental baffles inside the shell side along with the semicircular turbulators in the tube side and carried out the analysis for the heat exchanger model. In the fourth case inserting without sealer baffles which are considering decreasing the surface area of the baffles of about 32% in the total

area of the baffle [13] and without inserting the turbulators and analysis is carried out for the heat exchanger model. In fifth case inserting without sealer baffles with oval shaped holes on the baffles in shell side and there is no turbulators in the tube side. Here we are trying to decrease the surface area of the baffle which restrict the fluid flow by making the eight oval shaped holes on per baffle, these oval shaped holes are decreases the surface area of about 11%. Totally we

get a decreased area of including without sealer baffle and oval shaped holes of about 43%. By decreasing the surface area will have the decreased pressure drop so this is the reason for the decreasing the surface area.

The oval shaped holes have a more heat transfer rate compare to the other designs like circular, cam shaped or square holes etc. this is the reason for inserting the oval shaped holes on the baffles[2].

The analysis is carried out for all the five cases and results obtained for all the five cases for heat transfer coefficient, Pressure drop, surface temperature and turbulent kinetic energy are given below.

Models

Fig 1. Shell and tube heat exchanger with baffles

Fig 2. Shell and tube heat exchanger without baffles

Fig 3. Shell and tube heat exchanger with baffles and semicircular turbulators

Fig 4. Shell and tube heat exchanger without sealer baffles and without turbulators

Fig 5. Shell and tube heat exchanger without sealer baffles with oval shaped holes on the baffles and without turbulators

CFD Meshing

Fig 6. Mesh generated for the heat exchanger with baffles

Fig 7. Mesh generated for the heat exchanger without baffles

Fig 8. Mesh generated for the semicircular turbulators inside the tubes

Viscosity, µ = 12.9648 kg/ m sec.

Boundary conditions[3]

(i) Shell side

Mass flow rate of 5.517 kg/sec is imposed at inlet of the shell, along with the temperature value of 472K.

Fig 9. Mesh generated for without sealer baffles inside the shell

Fig 10. Mesh generated for without sealer baffles with oval shaped holes on the baffles

Fluid properties [3]

The properties of the hot fluid (Kerosene) and cold fluid (Crude oil) are taken at averaged temperatures in the design calculations. Hence the same values have been considered in the CFD analysis.

1. Shell side fluid (Kerosene, Tavg=419.26 K)

   Density, = 779 Kg/m3

   Thermal conductivity, K= 0.1288 W/m K. Specific heat, Cp = 2.46KJ/kg K. Viscosity, µ = 1.5485 kg/ m sec.

2. Tube side fluid (Crude oil, Tavg=330.27 K)

Density, =854Kg/m3

Thermal conductivity, K = 0.1332 W/m K. Specific heat, Cp = 2.05KJ/kg K.

Outflow conditions are imposed at the outlet of the shell.

1. Tube side

   Mass flow rate of 18.77kg/sec is imposed at the inlet of each tube, along with the temperature value of 311K.

   Outflow conditions are imposed at the outlet of each tube.

   Case 1: Results for the heat exchanger with baffles and without turbulators

   Fig 11. Heat transfer coefficient on tube surfaces with baffles and withoutturbulators

   Fig 12. Pressure drop with baffles and without turbulators

   Fig 13. Surface temperature of tubes with baffles and without turbulators

   Case 2: Results for the heat exchanger without baffles and withoutturbulators

   Fig 14. Heat transfer coefficient on tube surfaces without baffles and without turbulators

   Fig 15. Pressure drop without baffles and without turbulators

   Fig 16. Surface temperature of tube without baffles and without turbulators

   Case 3: Results for the heat exchanger with baffles and with turbulators

   Fig 17. Heat transfer coefficient on tube surfaces with baffles and turbulators

   Fig 18. Pressure drop with baffles and turbulators

   Fig 19. Surface temperature of tube with baffles and turbulators

   Case 4: Results for the heat exchanger without sealer baffles and without turbulators

   Fig 20. Heat transfer coefficient on tube surfaces without sealer baffles and without turbulators

   Fig 21. Pressure drop without sealer baffles and without turbulators

   Fig 22. Surface temperature on tube walls for without sealer baffles and without turbulators

   Case 5: Results for the heat exchanger without sealer baffles with oval shaped holes on the bafflesand without turbulator model

   Fig 23. Heat transfer coefficient fortubes without sealer with oval shaped holes on the baffles and without turbulators

   Fig 24. Pressure drop without sealer with oval shaped holes on the baffles and without turbulators

   Fig 25. Surface temperature for the tubes without sealer with oval shaped holes on the baffles and without turbulators

   Table 1. Validation of CFD results with theoretical results for with baffles and without turbulators

   Location	Parameters	Theoretical results	CFD results	Remark %
   Tube Side	Mass flow rate, m (kg/sec)	18.77	18.77	0.00
   	Inlet Temperature, ti (K)	310.92	310.92	0.0
   	Outlet Temperature, to (K)	349.81	351.74	0.55
   	Heat transfer coefficient, h (W/m2K)	686.67	702	2.10
   	Pressure Drop, P (kPa)	63.434	67.80	6.40

   From Table 1. is observed that there is a close prediction of theoretical results with that results obtained by the CFD analysis for with baffles and without turbulator model. There is an error of around ±6.5%, which is acceptable and leads to the further analysisand also pressure drop obtained by CFD analysis is within the allowable pressure drop.

   Table 2. Outlet temperature values predicted by CFD analysis

   Location	Inlet Temperature (K)	Outlet temperature, t (K)
   		Without baffles (Plain)	With baffles	With baffles and turbulators	Without sealer baffles	Without sealer and oval shaped holes on the baffles
   Tube 1	310.92	350.08	351.80	354.30	352.90	353.47
   Tube 2	310.92	350.03	352.60	355.10	353.60	354.42
   Tube 3	310.92	348.99	350.71	353.21	351.71	352.63
   Tube 4	310.92	348.09	351.88	354.38	352.88	353.76

   Table 3. Heat transfer coefficient values predicted by CFD analysis

   Sl.No	Location	Heat transfer coefficient, h (W/m2K)
   		Without baffles (Plain)	With baffles	With baffles and turbulator	Without sealer baffles	Without sealer and oval shaped holes on baffles
   1	Tubes	680.5	701	729	725	723

   Table 4. Pressure drop predicted by CFD analysis

   Location	Pressure drop, P (kPa)
   	Without baffles (Plain)	With baffles	With baffles and turbulators	Without sealer baffles	Without sealer and oval shaped holes on baffles	Allowable pressure drop
   Tube side	52.0	67.80	69.40	65.30	63.70	68.95

   Conclusion

   • In this the three dimensional model is studied for the shell and tube heat exchanger and CFD analysis is carried out for the Heat exchanger unit with different designs of baffles and semicircular turbulators.

   • Investigated for augmentation of heat transfer coefficient, temperature and variation in pressure drop for the five models.

   • Enhanced heat transfer coefficient of 3.01% for with baffles model, 7.1% for with baffles and turbulator model, and 6.5% for without sealer baffles and without turbulator model, 6.2% for without sealer with oval shaped holes on the baffles and without turbulator model compare to the plain model.

   • Increase in outlet temperature of tube of about 2.5 K for with baffles, 4.9 K for with baffles and turbulators, 3.48 K for without sealer baffles and without turbulators,4.2Kfor without sealer with oval shaped holes on the baffles and without turbulators compare to the plain model.

   • There is an increase in turbulent kinetic energy of about 38.17% for with baffles, 54.9% for with baffles and turbulators, 45.7% for without sealer baffles and without turbulators, 50.9% for without sealer with oval shaped holes on the baffles and without turbulators as compare to the plain model.

   • The pressure drop also increases 23.3% for with baffles, 20.36% for without sealer baffle and without turbulators, 18.36% for without sealer with oval shaped holes on the baffles and without turbulators compare with the plain model.

• The pressure drop is increased more of about 25.07% for with baffles and turbulators compare with the plain model. The pressure drop is exceeding the allowable limit of 68.95 kPa.

• By analyzing all the cases we have got desired results in fifth case that is without sealer baffles with oval shaped holes on the baffles and without turbulator model, so this is the best and safe design compare to all the cases.

References

1. Anil Singh Yadav, Effect of Half Length Twisted-Tape Turbulators on Heat Transfer and Pressure Drop Characteristics inside a Double Pipe U-Bend Heat Exchanger Jordan Journal of Mechanical and Industrial Engineering,2009.

2. Chen, Y., Fiebig, M. and Mitra, N.K., 1998b. Conjugate Heat Transfer of a Finned Oval Tube Part (B): Heat Transfer Behaviors. Numerical Heat Transfer A-33, 387-401.

3. Donald Q. Kern Process Heat Transfer Text Book, Associate, and Professional Lecturer in Chemical Engineering Case Institute of Technology, Tata McGraw Hill Edition 1997.

4. H. Shokouhmand, M.R. Salimpour, M.A. Akhavan-Behabadi, 2007, Experimental investigation of shell and coiled tube heat exchangers using wilsonplots International Communications in Heat and Mass Transfer 35 (2008) 8492 .

5. Hakan Karakaya, Aydin Durmus, 2013, Heat transfer and exergy loss in conical spring turbulators International Journal of Heat and Mass Transfer 60 (2013) 756762.

6. J. Herpe, D. Bougeard, S. Russeil, M. Stanciu1, Numerical investigation of local entropy production rate of a finned oval tube with vortex generators , International Journal of Thermal Sciences, Vol 48, N°5, pp 922-935, 2009.

7. S. Eiamsa-ard, P. Promvonge, 2006, Heat transfer characteristics in a tube fitted with helical screw-tape with/without core-rod inserts International Communications in Heat and Mass Transfer 34 (2007) 176185.

8. S. Eiamsa-ard, P. Promvonge, 2006, Experimental investigation of heat transfer and friction characteristics in a circular tube fitted with V-nozzle turbulatorsInternational Communications in Heat and Mass Transfer 33 (2006) 591600.

9. S. Eiamsa-ard, K. Wongcharee, S. Sripattanapipat, 2009, 3-D Numerical simulation of

   swirling flow and convective heat transfer in a circular tube induced by means of loose-fit twisted tapes International Communications in Heat and Mass Transfer 36 (2009) 947955.

10. S. Wang et al. / Applied Thermal Engineering 29 (2009) 24332438, An experimental investigation of heat transfer enhancementfor a shell- and-tube heat exchanger Applied Thermal Engineering 29 (2009) 24332438.

11. Ting Maa,b, Qiu-wang Wang a, Min Zenga, Yi-tung Chen b, Yang Liu b, VijaisriNagarajan, 2012, Study on heat transfer and pressure drop performances of ribbed channel in the high temperature heat exchanger Applied Energy 99 (2012) 393401.

12. V. Kongkaitpaiboon, K. Nanan, S. Eiamsa- ard, Experimental investigation of convective heat transfer and pressure loss in a round tube fitted with circular-ring Turbulators International Communications in Heat and Mass Transfer 37 (2010) 568574,Elsevier,2010.

13. Veysel Ozceyhan a, SibelGunes a, Orhan Buyukalaca b, NecdetAltuntop, 2008, Heat transfer enhancement in a tube using circular cross sectional rings separated from wall V. Ozceyhan et al. / Applied Energy 85 (2008) 9881001.

14. ang Yongqing, GuXin, Wang Ke, Dong Qiwu, 2012, Numerical investigation of shell-side characteristics of H-shape baffle heat exchanger Heat Transfer and Energy Saving of Henan Province; Zhengzhou University, Zhengzhou 450002.

15. Yan Li, Xiumin Jiang, Xiangyong Huang, JigangJia, Jianhui Tong, 2011, Optimization of high-pressure shell-and-tube heat exchanger for syngas cooling in an IGCC International Journal of Heat and Mass Transfer 53 (2010) 45434551.