Numerical simulation of heat transfer and hydraulic losses of air-cooled exhaust-shaft apparatuses

The article presents the numerical simulation results on heat transfer and hydraulic losses of air-cooled exhaust-shaft apparatuses. Studies were made on air-cooled apparatuses in which four-row bundles of staggered finned tubes were placed. Numerical simulation used a gas dynamic solver Ansys Fluent. Menter’s shear stress transport κ-ω model was invited to close the Reynolds equations. The obtained numerical results allowed us to visualize air flow in the bundle and the exhaust shaft, as well as to establish an inhomogeneous distribution of velocities and temperatures. We found that the temperature distribution in the flow passing through the exhaust shaft depends on the height of the exhaust shaft. We also established that at small shaft heights in the wake behind a bundle because of the wake oscillatory motion, the dynamic and temperature inhomogeneous distributions take place, resulting in the cold air suction through the shaft from the environment. With an increase in the shaft height, the inhomogeneous temperature distribution moves upstream the air flow in the shaft and the inhomogeneous temperature distribution attenuates. We can say that maximum heat transfer at the same hydraulic losses is achieved when mounting a shaft with a height of H > 1.16 m. The results obtained can be used for the modernization of existing air-cooled apparatus, as well as for the design of new devices with an exhaust shaft.

1. Bessonnyi A. N., Kuntysh V. B., eds. Basics of Calculation and Design of Air Cooling Heat Exchangers. St. Petersburg, Nedra Publ., 1996. 512 p. (in Russian).

2. Korolev I. I., Genova E. V., Benklyan S.E. On combined CHPP cooling systems. Teploenergetika= Thermal Power Engineering, 1996, no. 11, pp. 49–55 (in Russian).

3. Bystrov Ju. A., Isaev S. A., Kudryavtsev N. A., Leont’ev A.I. Numerical Modeling of Vortex Intensification of Heat Transfer in Tube Bundles. St. Petersburg, Sudostroenie Publ., 2005. 392 p. (in Russian).

4. Kong Y., Wang W., Zuo Z., Yang L., Du X., Yang Y. Combined air-cooled condenser layout with in line configured fiined tube bundles to improve cooling performance. Applied Thermal Engineering, 2019, vol. 154, pp. 505–518. https://doi. org/10.1016/j.applthermaleng.2019.03.099

5. Kuntysh V. B., Pozdnyakova A. V., Melehov V.I. Heat transfer by natural convection of a single row of vertical finned pipes of heaters of drying chambers. Lesnoi zhurnal = Russian Forestry Journal, 2002, no. 2, pp. 116–121 (in Russian).

6. Zorin V.M. Nuclear Power Plants. Moscow, MEI Publ., 2012. 672 p. (in Russian).

7. Kuntysh V. B., Samorodov A. V., Sukhotskii A.B. Engineering method of thermal calculation of the air cooling apparatus in the mode of free-convective heat exchange. Khimicheskoe i neftegazovoe mashinostroenie= Chemical and Petroleum Engineering, 2013, no. 12, pp. 3–6 (in Russian).

8. Samorodov A.V. Improving the Methods of Thermal Calculation and Design of Air Cooling Devices with Checkerboard Finned Bundles. Arkhangelsk, 1999. 176 p. (in Russian).

9. Cheng T.S. Characteristics of mixed convection heat transfer in a lid-driven square cavity with various Richardson and Prandtl numbers. International Journal of Thermal Sciences, 2011, vol. 50, no. 2, pp. 197–205. http://dx.doi.org/10.1016/j. ijthermalsci.2010.09.012

10. Martynenko O. G., Sokovishin Yu. A. Heat Exchange by Mixed Convection. Minsk, Nauka i tekhnika Publ., 1975. 256 p. (in Russian). 11. Mil’man O.O. Experimental study of heat exchange during natural air circulation in the model of an air condenser with an exhaust shaft. Teploenergetika = Thermal Engineering, 2005, no. 5, pp. 16–19 (in Russian).

11. Vasil’ev Yu. N., Margolin G.A. Cooling Systems of Compressor and Oil Pumping Stations. Moscow, Nedra Publ., 1977. 222 p. (in Russian).

12. Gabdrakhmanov A.A. Improvement of the Efficiency of the Equipment for Air Cooling Apparatus on the Main Conductors. Ufa, 2007. 24 p. (in Russian).

13. Kumar A., Joshi J. B., Nayak A. K., Vijayan P. K. 3D CFD simulations of air cooled condenser-II: Natural draft around a single finned tube kept in a small chimney. International Journal of Heat and Mass Transfer, 2016, vol. 92, pp. 507– 522. https://doi.org/10.1016/j.ijheatmasstransfer.2015.07.136

14. Marshalova G.S. Thermal Desing and Making of Air-Cooled Exhaust Shaft Apparatus. Minsk, 2019. 153 p. (in Russian)

15. Marshalova G. S., Sukhotskii A. B., Kuntysh V.B. Enhancing Energy Saving in Air Cooling Devices by Intensifying External Heat Transfer. Khimicheskoe i neftegazovoe mashinostroenie = Chemical and Petroleum Engineering, 2020, no. 2, pp. 3–7 (in Russian).

16. Marshalova G. S., Sukhotskii A.B. Aerodynamic drag at small Reynolds numbers and the method of calculation of the air velocity in one- and many-row finned beams with an exhaust shaft. Vestsі Natsyianal’nai akademіі navuk Belarusі. Seryia fіzіka-matematychnykh navuk = Proceedings of the National Academy of Sciences of Belarus. Physics and Mathematics series, 2021, vol. 57, no. 1, pp. 108–118 (in Russian). https://doi.org/10.29235/1561-2430-2021-57-1-108-118

17. Durbin P. A., Pettersson-Reif B.A. Statistical Theory and Modeling for Turbulent Flows. Willey, 2001. 367 p.

18. ANSYS Fluent Theory Guide. Release 15.0 (2013). Available at: http://www.pmt.usp.br/academic/martoran/notasmodelosgrad/ANSYS%20Fluent%20Theory%20Guide%2015.pdf (accessed 16 April 2022).

19. Menter F. R., Kuntz M., Langtry R. Ten years of industrial experience with the SST turbulence model. Turbulence. Heat and Mass Transfer, 2003, vol. 4, pp. 625–632.

20. Alam Md. Mahbub, Moriya M., Sakamoto H. Aerodynamic characteristics of two side-by-side circular cylinders and application of wavelet analysis on the switching phenomenon. Journal of Fluids and Structures, 2003, vol. 18, no. 3–4, pp. 325–346. https://doi.org/10.1016/j.jfluidstructs.2003.07.005

21. Alam Md. Mahbub, Zhou Y. Flow around two side-by-side closely spaced circular cylinders. Journal of Fluids and Structures, 2007, vol. 23, no. 5, pp. 799–805. https://doi.org/10.1016/j.jfluidstructs.2006.12.002

22. Zhukova Yu. V., Terekh A. M., Rudenko A.I. Convective heat transfer and drag of two side-by-side tubes in the narrow channel at different Reynolds number. Doklady Natsional’noi akademii nauk Belarusi = Doklady of the National Academy of Sciences of Belarus, 2018, vol. 62, no. 6, pp. 756–762 (in Russian).