ÜÇ KATMANLI GÖZENEKLİ YAKICIDA ÖN KARIŞIMSIZ YANMANIN FLAMELET MODELİ İLE SAYISAL İNCELENMESİ

Abstract

Bu çalışmanın amacı üç farklı gözeneklilik yoğunluğuna sahip bir yakıcıyı sayısal olarak incelemektir. Bu kanalda ön karışımsız yanma, gözenekli katı ortam ile akışkan arasında ısıl denge olmadığı kabülü ile ısıl dengesiz enerji denklemleri kullanılarak modellenmiştir. Yanma modelinde akış ve yanma mekanizmaları flamelet tablolama modeli ile ayrılmıştır ve böylece hesaplama maliyeti düşürülmüştür. Metanın hava ile yanması GRI 3.0 mekanizması ile modellenmiştir. Üçünçü gözenekli katmanın zararlı gaz salımına etkisini gözlemlemek için, son katmanın 8-30 PPI aralığında değişen farklı gözeneklilik değerleri ile hesaplamalar yapılmıştır. Ek olarak, yakıcı gücünün ve fazla hava oranının yakıcıya etkisi de incelenmiştir. Hesaplamalar sonucunda sıcaklık dağılımı ve türlerin kütle kesirleri elde edilmiştir. Ön karışımsız yanmada tepkime tam oranlı şartlarda gerçekleşeceğinden yakıcı içerisindeki en yüksek sıcaklık her durum için benzer bulunmuştur. Yakıcının NOx ve CO salım değerleri uluslararası standartlar ile kıyaslanmıştır ve CO salımlarının her durumda standartların altında olduğu fakat NOx salımlarının sadece yüksek hava oranları ve ısıl güçler ile düşük çıktığı görülmüştür. Ek olarak üçüncü katmanın gözenek yoğunluğu (PPI değeri) düşürüldükçe zararlı gaz salım değerlerinin de çokça düştüğü görülmüştür.

Keywords

• Gözenekli ortam
• Yanma
• Flamelet modeli
• Isıl dengesiz model

NUMERICAL INVESTIGATION OF NON-PREMIXED COMBUSTION INSIDE A THREE LAYERED POROUS BURNER WITH FLAMELET MODEL

Abstract

Purpose of this study is to numerically investigate combustion within a porous channel, which has three layers with different pore densities. Non-premixed combustion inside the porous channel is modelled with thermal non-equilibrium energy equations. Flow and chemistry are decoupled with tabulated chemistry using flamelets, thereby reducing the computational cost. GRI 3.0 mechanism is used to account for methane/air combustion. Simulations are performed for different pore densities at the third layer in 8-30 PPI range. Also, the effects of thermal power and excess-air-ratio (EAR) are investigated for the porous burner. Temperatures and species mass fraction distributions are obtained. Maximum temperature in the burner found to be similar for all cases since combustion occurs in stoichiometric conditions at the flame front as a result of the non-premixed combustion model. NOx and CO emissions values of all simulations are compared against international gas emission standards. This comparison showed that while CO emissions are always below all international standards, NOx emissions are below these limits only for high values of excess air ratio and thermal power. Besides, as the pore density of the third layer is decreased, the values of emissions decrease strongly.

Keywords

• Porous media
• Combustion
• Flamelet model
• Thermal Non-equilibrium

References

1. Barra, A. J. and Ellzey, J. L. (2004) ‘Heat recirculation, heat transfer in porous burners’, Combust. Flame, 137, pp. 230–241.
2. Barra, A. J. et al. (2003) ‘Numerical study of the effects of material properties on flame stabilization in a porous burner’, Combust. Flame, 134, pp. 369–379. doi: 10.1016/S0010-2180(03)00125-1.
3. Baytas, A. C. (2003) ‘Thermal Non-Equilibrium natural convection in a square enclosure filled with a heat generating solid phase, non-Darcy porous medium’, International Journal of Energy Research, 27, pp. 975–988. doi: 10.1002/er.929.
4. Baytas, A. C. and Pop, I. (2002) ‘Free convection in a square porous cavity using a thermal nonequilibrium model’, International Journal of Thermal Sciences, 41(9), pp. 861–870. doi: 10.1016/S1290-0729(02)01379-0.
5. Bouma, P. H. and De Goey, L. P. H. (1999) ‘Premixed Combustion on Ceramic Foam Burners’, Combust. Flame, 119, pp. 133–143. doi: 10.1016/S0010-2180(99)00050-4. Carbonell, D. et al. (2009) ‘Flamelet mathematical models for non-premixed laminar combustion’, Combustion and Flame, 156(2), pp. 334–347. doi: 10.1016/j.combustflame.2008.07.011.
6. Coutinho, J. E. A. and de Lemos, M. J. S. (2012) ‘Laminar flow with combustion in inert porous media’, Int. Communications in Heat and Mass Transfer, 39, pp. 896–903. doi: 10.1016/j.icheatmasstransfer.2012.06.002.
7. Durst, F., Trimis, D. and Pickenacker, K. (1996) ‘Compact porous medium burner and heat exchanger for household applications.’, European Union commission project report, pp. 1–85.
8. Ergun, S. (1952) ‘Fluid flow through packed columns’, Chemical Engineering and Progress, 8(2), pp. 89–94.

9. Farzaneh, M. et al. (2012) ‘Numerical investigation of premixed combustion in a porous burner with integrated heat exchanger’, Heat and Mass Transfer. Springer-Verlag, 48(7), pp. 1273–1283. doi: 10.1007/s00231-012-0966-1.
10. Fu, X. and Viskanta R. Gore, J. P. (1998) ‘Measurement and corrolation of volumetric heat transfer coefficients of cellular ceramics.’, Experimental Thermal and Fluid Science, 17, pp. 285–293.
11. Hirschfelder, J. O., Curtiss, C. F. and Bird, R. B. (1955) ‘Molecular theory of gases and liquids. Wiley, New York, 1954’, Journal of Polymer Science, 17(83), p. 116. doi: 10.1002/pol.1955.120178311.
12. Hsu, P. F., Howell, J. R. and Matthews, R. D. (1993) ‘A numerical investigation of premixed combustion within porous inert media’, Journal of Heat Transfer, 115(3), pp. 744–750. doi: 10.1115/1.2910746.
13. Keramiotis, C., Stelzner, B. and Trimis D. Founti, M. (2012) ‘Porous burners for low emission combustion: An experimental investigation’, Energy, 45, pp. 213–219. doi: 10.1016/j.energy.2011.12.006.
14. Khanna, V., Goel, R. and Ellzey, J. L. (1994) ‘Measurements of Emissions and Radiation for Methane Combustion with in a Porous Medium Burner’, Combustion Science and Technology, 99, pp. 133–142. doi: 10.1080/00102209408935429.
15. Kuwahara, F., Shirota, M. and Nakayama, A. (2001) ‘A numerical study of interfacial convective heat transfer coefficient in two-energy equation model for convection in porous media’, International Journal of Heat and Mass Transfer. Pergamon, 44(6), pp. 1153–1159. doi: 10.1016/S0017-9310(00)00166-6.
16. Lu, L. et al. (2009) ‘Computationally efficient implementation of combustion chemistry in parallel PDF calculations’, Journal of Computational Physics. Academic Press, 228(15), pp. 5490–5525. doi: 10.1016/j.jcp.2009.04.037.
17. Macdonald, I. F. et al. (1979) ‘Flow Through Porous Media: Ergün equation revisited’, Indust. Eng. Chem. Fundamentals, 18, pp. 199–208. doi: 10.1021/i160071a001.
18. Mengi, S.,Tunçer, O., Baytaş, A.C., “Sandia-D Alevi Simülasyonunda Radyasyon Etkisinin Flamelet Modeli Kullanılarak İncelenmesi”, 20. Ulusal Isı Bilimi ve Tekniği Kongresi, Balıkesir, Türkiye, Eylül 2015
19. Mishra, S. C. et al. (2006) ‘Heat transfer analysis of a two-dimensional rectangular porous radiant burner’, Int. Commun. Heat Mass Transfer, 33, pp. 467–474. doi: 10.1016/j.icheatmasstransfer.2005.12.006.
20. Modest, M. F. (1993) Radiative Heat Transfer. Mc Graw Hill International Editions. doi: 10.1017/CBO9781107415324.004.
21. Patankar, S. (1980) Numerical heat transfer and fluid flow. CRC press.
22. Peters, N. (1984) ‘Laminar diffusion flamelet models in non-premixed turbulent combustion’, Progress in Energy and Combustion Science. Pergamon, 10(3), pp. 319–339. doi: 10.1016/0360-1285(84)90114-X.
23. Pope, S. B. (2000) ‘Computationally efficient implementation of combustion chemistry using in situ adaptive tabulation’, Combustion Science and Technology, 161, pp. 113–137.
24. Rashed, A. H. (2002) ‘Properties and characteristics of silicon Carbide’. Decatur, TX. doi: 10.5772/615.
25. Scheffler, M., Colombo, P. and Wiley (2005) Cellular ceramics : structure, manufacturing, properties and applications. Wiley-VCH. Available at: https://books.google.com.tr/books?hl=tr&lr=&id=LP6HpxX0A8MC&oi=fnd&pg=PR5&dq=scheffer+colombo+cellular+ceramics+structure+manufacturing&ots=Z7YtG8TTBe&sig=756Q5nXisaKWyg-jWxIzhAOFZyI&redir_esc=y#v=onepage&q=scheffer colombo cellular ceramics structure manufacturing&f=false (Accessed: 27 September 2017).
26. Shakiba, S. A. et al. (2015) ‘Effects of foam structure and material on the performance of premixed porous ceramic burner’, Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 229(2), pp. 176–191. doi: 10.1177/0957650914558166.
27. Smucker, M. T. and Ellzey, J. L. (2005) ‘Computational experimental study of two-section porous burner’, Combust. Sci. Technol., 176, pp. 1171–1189. doi: 10.1080/00102200490457385.
28. Takeno, T. and Sato, K. (1979a) ‘A theoretical and experimental study on an excess enthalpy flame’, in ICOGER. doi: 10.1016/S0082-0784(81)80052-5.
29. Takeno, T. and Sato, K. (1979b) ‘An Excess Enthalpy Flame Theory’, - Combustion Science and Technology, 20(1–2), pp. 73–84. doi: 10.1080/00102207908946898.
30. Trimis, D. et al. (2000) Porous Medium Combustor versus Combustion Systems with Free Flames.
31. Turns, Stephen R. ‘Introduction to combustion’. Vol. 287. McGraw-Hill Companies, 1996.
32. Van Oijen, J. A. and De Goey, L. P. H. (2000) ‘Modelling of Premixed Laminar Flames using Flamelet-Generated Manifolds’, Combustion Science and Technology, 161, pp. 113–137. doi: 10.1080/00102200008935814.
33. Vijaykant, S. and Agrawal, A. K. (2007) ‘Liquid fuel combustion within silicon-carbide coated carbon foam’, Exp. Therm. Fluid Sci., 32, pp. 117–125. doi: 10.1016/j.expthermflusci.2007.02.006.
34. Weinberg, F. J. (1971) ‘Combustion Temperatures: The Future?’, Nature, 233(5317), pp. 239–241. doi: 10.1038/233239a0.
35. Zhou, X. Y. and Pereira, J. C. F. (1997) ‘Numerical study on combustion and pollutions formation in inert non homogenous porous media’, Combustion Sci. Technol., 130, pp. 335–364. doi: 10.1080/00102209708935748