Kanat – Borulu Isı Eşanjörlerinin Akım ve Isı Transfer Özelliklerinin Belirlenmesinde Farklı Duvar Fonksiyonlarının Etkisi

Öz

: Bu çalışmada, Fluent yazılım programında mevcut bulunan duvar fonksiyonlarının, kanat borulu ısı eşanjörlerinde akım ve ısı transfer özelliklerinin belirlenmesindeki etkileri Reynolds Sayılarının 500 ≤ Re ≤ 6000 aralığında ve Fs = 0.233 boyutsuz plaka açıklığında araştırılmış ve sonuçlar deneysel çalışma ile karşılaştırılmıştır. Bilindiği üzere duvar fonksiyonları, viskoziteden etkilenmiş bölge ile tamamen türbülanslı akışın hakim olduğu bölge arasında bir köprü görevi kurmaktadır. Dö sıralı, saptırmalı boru konfigürasyonuna ve dalgalı plakaya sahip bir kanat- borulu ısı eşanjöründeki akış ve ısı transfer özelliklerinin belirlenmesinde Standard k-ε and RNG k-ε türbülans modelleri kullanılmıştır. Bu ısı eşanjör modeli literatürdeki bir deneysel çalışmadan alınmış ve deneye en yakın sonucu veren duvar fonksiyonu İyileştirilmiş Duvar Fonksiyonu olarak belirlenmiştir.

Anahtar Kelimeler

• Türbülans modelleri, duvar fonksiyonları, kanat-borulu ısı eşanjörü

EFFECT OF DIFFERENT WALL FUNCTIONS ON THE PREDICTION OF FLOW AND HEAT TRANSFER CHARACTERISTICS IN PLATE FIN AND TUBE HEAT EXCHANGERS

Abstract

In the present study, effects of wall functions available in the Fluent software on the fluid flow and heat transfer characteristics of a plate fin and tube heat exchanger are investigated in the range of 6000Re500 ≤≤ for a non-dimensional fin spacing of 233.0=sF and the results are compared with experimental data. As it is well-known, wall functions are used to bridge the viscosity-affected region between the wall and the fully turbulent region in the flow domain. Both Standard k-ε and RNG k-ε turbulence models are employed in order to predict the flow and heat transfer characteristics inside the flow passage of the plate fin and tube heat exchanger comprised of four-row of staggered tube layout with wavy fin configuration. The test heat exchanger model is selected from the experimental work exists in the literature and the best wall function that has close agreement with the experimental data is chosen as Enhanced Wall Treatment.

Keywords

• Turbulence models, wall functions, plate fin and tube heat exchangers

Kaynakça

1. Barsamian, H.R., Hassan, Y.A., 1997, Large Eddy simulation of turbulent crossflow in tube bundles, Nucl. Eng. Des., 172,103-122.
2. Critoph, R.E., Holland, M.K., Fisher, M., 1999, Comparison of steady state and trasnsient methods for measurement of local heat transfer in plate fin-tube heat exchangers using liquid cristal thermography with radiant heating, Int. J. Heat Mass. Tran., 42, 1-12.
3. FLUENT DYNAMICS SOFTWARE, 1998, FLUENT (Ver. 5.5). Goldstein, L.G., Sparrow, E.M., 1976, Experiments on the transfer characteristics of a corrugated fin and tube heat exchanger configuration, J. Heat. Trans.-T. ASME, 98, Feb., 26-34
4. Kim, N.H., Yun, J.H., Webb, R.L., 1997, Heat transfer and friction correlations for wavy plate fin- andtube heat exchangers, Transactions of the ASME, 119, 560-567. Kundu, D., Skeikh, A.H., Lou, D.Y.S., 1992, Heat transfer in crossflow over cylinders between two
5. parallel plates, Numer. Heat Tr. A-Appl., 114, 558-564. Lozza, G., Merlo, U., 2001, An experimental investigation of heat transfer and friction losses of interrupted and wavy fins for fin-and-tube heat exchangers, Int. J. Refrig., 24, 409-416.
6. Madi, M.A., Johns,R..A.,Heikal, M.R., 1998, Performance characteristics correlation for round tube and plate finned heat exchangers, Int. J. Refrig., 21, 7, 507-517.
7. Mendez, R.R., Sen, M., Yang, K.T., Mcclain, R., 2000. Effect of fin spacing on convection in a plate fin and tube heat exchanger, Int. J. Heat Mass. Tran., 43, 39-51.
8. Rocha, L.A.O., Saboya, F.E.M., Vargas, J.V.C., 1997, A comparative study of elliptical and circular sections in one- and two- row tubes and plate fin heat exchangers, Int. J. Heat Fluid Fl., 18, 247-252.

9. Saboya, F.E.M., Sparrow, E.M., 1974, Local and average transfer coefficients for one row plate fin and tube heat exchanger configurations. J. Heat Transfer, Trans. ASME., August: 265-272.
10. Seshimo, Y., Fujii, M., 1991, An experimental study on the performance of plate fin and tube heat exchangers at low Reynolds Numbers, ASME/JSME Thermal Engineering Proceedings, 4, 449- 454.
11. Shah, R.K., Heikal, M.R., Thonon, B., 1997, Advances in numerical analysis of fluid flow, heat transfer, and flow friction characteristics of compact heat exchanger surfaces, Proceedings, Int. Symposium on Fluid Flow and Heat Transfer, Ankara, Turkey, 68-87.
12. Tzanetakis, N., Scott, K., Taama, W.M., Jachuck, R.J.J., 2004. Mass transfer characteristics of corrugated surfaces, Appl. Therm. Eng., 24, 13,1865-1875.
13. Valencia, A., Fiebig, M., Mitra, N.K., 1996, Heat transfer enhancement by longitudinal vortices in a fintube heat exchanger element with flat tubes, J. Heat Trans., 118, 209-211.
14. Wang, C.C., Fu, W.L., Chang, C.T., 1997, Heat transfer and friction characteristics of typical wavy finand- tube heat exchangers, Exp. Therm. Fluid Sci., 14, 174-186.
15. Wung, T.S., Chen, C.J., 1989, Finite analytic solution of convective heat transfer for tube arrays in crossflow: Part I- Flow field analysis, J. Heat Trans., 111, 633-640.
16. Yan, W.M., Sheen, P.J., 2000, Heat transfer and friction characteristics of fin and tube heat exchangers, Int. J. Heat Mass Trans., 43, 1651-1659.
17. Zhang, J., Kundu, J., Manglik, R.M., 2004, Effect of fin waviness and spacing on the lateral vortex structure and laminar heat transfer in wavy-plate-fin cores, Int. J. Heat Mass Trans., 47, 1719- 1730.