Ahmet Furkan URKUT, Efe Oğuzhan KARCI, Mehmed Rafet ÖZDEMİR

Transkritik Soğutma Çevrimlerinde Gaz Soğutucu Geometrisinin Sayısal Optimizasyonu

Geleneksel halokarbon bazlı soğutucu akışkanlar, küresel ısınmayı ve ozon tabakasını inceltme faktörlerini önemli ölçüde artırma eğilimindedir. Bu nedenle, araştırma topluluğunun dikkatini çeken ve hızla yaygın olarak uygulanan doğal bir soğutucu olarak CO2 önemli bir araç haline gelmektedir. Gaz soğutucu, CO2 transkritik soğutma sisteminde önemli bir bileşendir ve çalışma basıncının ve dolayısıyla güç tüketiminin belirlenmesi nedeniyle performansta önemli bir rol oynar. Bu araştırmada, günümüzde iklimlendirme, otomotiv ve havacılık gibi sektörlerde kullanılan dalgalı kanatçık geometrisine sahip bir CO2 gaz soğutucunun performans özellikleri kalorimetrik bir test odasında deneysel olarak belirlenmiştir. Deneysel sonuçlar, üç boyutlu sayısal modeli doğrulamak için ölçüt olarak kullanılmıştır. Analizler için laminer model ve realizable k - ɛ türbülanslı model kullanılmıştır. Ayrıca momentum ve enerji denklemlerini ayrıklaştırmak için second order upwind şeması kullanılmıştır. Buna göre, CO2 transkritik soğutma sisteminde optimum dalgalı kanatçık geometrisini belirlemek için Yanıt Yüzey Yöntemi (RSM) kullanılarak çok amaçlı bir optimizasyon işlemi gerçekleştirilmiştir. Gaz soğutucunun boyuna hatvesi, yarım enine hatvesi, boru dış çapı ve kanatçık hatvesi olmak üzere dört geometrik parametre optimize edilmiştir. Sonuçlara göre, yeni optimize edilmiş CO2 gaz soğutucusunun, endüstride kullanılan test edilmiş gaz soğutucu geometrisine kıyasla daha az basınç düşüşü ve daha yüksek ısı transfer kapasitesi sergilediği görülmüştür. Üç farklı giriş hızı için ortalama ısı transfer katsayısı iyileşmesinin %5,4 – 12,2 arasında olduğu, basınç düşüşünün ise % 175,08 – 188,58 oranında azaldığı görülmüştür.

Anahtar Kelimeler:

doğal soğutucular, ısı transferi katsayısı, gaz soğutucu, optimizasyon, dalgalı kanatçık, natural refrigerants, heat transfer coefficient, gas cooler, optimization, wavy fin

Numerical Optimization of Gas Cooler Geometry in Transcritical Refrigeration Cycles

Traditional halocarbon – based refrigerants tend to considerably increase global warming and ozone depletion factors. Therefore, CO2 is fast becoming a key instrument as a natural refrigerant which was widely applied and attracted the consideration of the research community. The gas cooler is an important component in the CO2 transcritical refrigeration system and plays a key role in the performance due to the determination of operating pressure consequently power consumption. In this research, the performance characteristics of a CO2 gas cooler having wavy fin geometry, which is currently used in industries such as air conditioning, automotive and aviation, was determined experimentally in a calorimetric test room. The experimental results was used as benchmark data to validate the three – dimensional numerical model. Laminar model and realizable k - ɛ turbulent model were employed for analyses. Moreover, the second order upwind scheme was considered to discretize momentum and energy equations. Accordingly, a multi-objective optimization process has been performed employing Response Surface Method (RSM) to determine the optimum wavy fin geometry in CO2 transcritical refrigeration system. Four geometrical parameters namely longitudinal pitch, half transverse pitch, tube outer diameter, and fin pitch of the gas cooler were optimized. According to results, the new optimized CO2 gas cooler exhibited lesser pressure drop and higher heat transfer capacity in comparison with the tested gas cooler geometry used in the industry. It was found that the overall heat transfer coefficient enhancement is between 5.4 – 12.2 % while pressure drop decreases about 175.08 – 188.58 % for three different inlet velocities.

Keywords:

natural refrigerants, heat transfer coefficient, gas cooler, optimization, wavy fin,

PDF

___

[1] Bolaji, B. O., & Huan, Z. (2013). Ozone depletion and global warming: Case for the use of natural refrigerant–a review. Renewable and Sustainable Energy Reviews, 18, 49-54.
[2] Rony, R. U., Yang, H., Krishnan, S., & Song, J. (2019). Recent advances in transcritical CO2 (R744) heat pump system: a review. Energies, 12(3), 457.
[3] ASHRAE. 15 & 34 Safety Standard for Refrigeration Systems and Designation and Classification of Refrigerants ISO 5149 Mechanical Refrigerating Systems Used for Cooling and Heating—Safety Requirements.
[4] Lachner Jr, B. F., Nellis, G. F., & Reindl, D. T. (2007). The commercial feasibility of the use of water vapor as a refrigerant. International Journal of Refrigeration, 30(4), 699-708.
[5] American Society of Heating, Refrigerating and Air-Conditioning Engineers (2014). ASHRAE Position Document on Natural Refrigerants. Inc., Atlanta, GA, USA.
[6] Gullo, P., Hafner, A., & Banasiak, K. (2018). Transcritical R744 refrigeration systems for supermarket applications: Current status and future perspectives. International Journal of Refrigeration, 93, 269-310.
[7] Cecchinato, L., & Corradi, M. (2011). Transcritical carbon dioxide small commercial cooling applications analysis. International Journal of Refrigeration, 34(1), 50-62.
[8] Kılıç, B. (2018). Thermo-Economic Analysis of Transcritical Carbon Dioxide Refrigeration Cycle. Avrupa Bilim ve Teknoloji Dergisi, (14), 152-156.
[9] Jang, J. Y., & Chen, L. K. (1997). Numerical analysis of heat transfer and fluid flow in a three-dimensional wavy-fin and tube heat exchanger. International Journal of Heat and Mass Transfer, 40(16), 3981-3990.
[10] Kim, M. H., & Bullard, C. W. (2002). Air-side thermal hydraulic performance of multi-louvered fin aluminum heat exchangers. International Journal of Refrigeration, 25(3), 390-400.
[11] Mon, M. S., & Gross, U. (2004). Numerical study of fin-spacing effects in annular-finned tube heat exchangers. International Journal of Heat and Mass Transfer, 47(8-9), 1953-1964.
[12] Tao, Y. B., He, Y. L., Huang, J., Wu, Z. G., & Tao, W. Q. (2007). Numerical study of local heat transfer coefficient and fin efficiency of wavy fin-and-tube heat exchangers. International Journal of Thermal Sciences, 46(8), 768-778.
[13] Lu, C. W., Huang, J. M., Nien, W. C., & Wang, C. C. (2011). A numerical investigation of the geometric effects on the performance of plate finned-tube heat exchanger. Energy Conversion and Management, 52(3), 1638-1643.
[14] Dong, J., Su, L., Chen, Q., & Xu, W. (2013). Experimental study on thermal–hydraulic performance of a wavy fin-and-flat tube aluminum heat exchanger. Applied Thermal Engineering, 51(1-2), 32-39.
[15] Santosa, I. M., Gowreesunker, B. L., Tassou, S. A., Tsamos, K. M., & Ge, Y. (2017). Investigations into air and refrigerant side heat transfer coefficients of finned-tube CO2 gas coolers. International Journal of Heat and Mass Transfer, 107, 168-180.
[16] Zhang, X., Ge, Y., Sun, J., Li, L., & Tassou, S. A. (2019). CFD Modelling of Finned-tube CO2 Gas Cooler for Refrigeration Systems. Energy Procedia, 161, 275-282.
[17] Javaherdeh, K., Vaisi, A., & Moosavi, R. (2018). The effects of fin height, fin-tube contact thickness and louver length on the performance of a compact fin-and-tube heat exchanger. International Journal of Heat and Technology, 36(3), 825-834.
[18] Zhang, X., Ge, Y., & Sun, J. (2020). CFD performance analysis of finned-tube CO2 gas coolers with various inlet air flow patterns. Energy and Built Environment, 1(3), 233-241.
[19] European Committee for Standardization, (2014), Heat exchangers - Forced convection air cooled refrigerant condensers - Test procedures for establishing performance (CSN EN 327), Retrieved from https://www.en-standard.eu/csn-en-327-heat-exchangers-forced-convection-air-cooled-refrigerant-condensers-test-procedures-for-establishing-performance/
[20] European Committee for Standardization, (2014) Heat exchangers - Forced convection unit air coolers for refrigeration - Test procedures for establishing the performance (CSN EN 328), Retrieved from https://www.en-standard.eu/csn-en-328-heat-exchangers-forced-convection-unit-air-coolers-for-refrigeration-test-procedures-for-establishing-the-performance/
[21] Coleman, H. W., & Steele, W. G. (2018). Experimentation, Validation, and Uncertainty Analysis for Engineers. John Wiley & Sons, Haboken, NJ, USA.
[22] Fluent, A. (2009). Ansys Fluent 12.0 Theory Guide. ANSYS Inc., Canonsburg, PA.
[23] Menéndez-Pérez, A., Pita-Cantos, M. T. L., & Borrajo-Pérez, R. (2019). Determination of the optimum louver angle of a louvered fin with elliptical tubes. Ingeniería Mecánica, 22(1), 07-13.
[24] Gupta, A., Roy, A., Gupta, S., & Gupta, M. (2020). Numerical investigation towards implementation of punched winglet as vortex generator for performance improvement of a fin-and-tube heat exchanger. International Journal of Heat and Mass Transfer, 149, 119171.
[25] Bilir, L., Ozerdem, B., Erek, A., & Ilken, Z. (2010). Heat transfer and pressure drop characteristics of fin-tube heat exchangers with different types of vortex generator configurations. Journal of Enhanced heat transfer, 17(3).
[26] Okbaz, A., Pınarbaşı, A., Olcay, A. B., & Aksoy, M. H. (2018). An experimental, computational and flow visualization study on the air-side thermal and hydraulic performance of louvered fin and round tube heat exchangers. International Journal of heat and Mass Transfer, 121, 153-169.
[27] Balkanlı, B., Yurddaş, A., & Aksoy, Y. (2020). Split klimalarda kullanılan ısı değiştiricilerinde kanatçık etkisinin sayısal analizi. Pamukkale Üniversitesi Mühendislik Bilimleri Dergisi, 26(4), 689-699.
[28] Yeşil, Ç. (2007). Kanatlı borulardaki dış akış ve konjuge ısı transferi mekanizmasinin sayısal olarak incelenmesi. Yüksek Lisans Tezi, Yıldız Teknik Üniversitesi, Türkiye.
[29] Damavandi, M. D., Forouzanmehr, M., & Safikhani, H. (2017). Modeling and Pareto based multi-objective optimization of wavy fin-and-elliptical tube heat exchangers using CFD and NSGA-II algorithm. Applied Thermal Engineering, 111, 325-339.
[30] Box, G. E., & Draper, N. R. (1987). Empirical model-building and response surfaces. John Wiley & Sons.
[31] Kumari, M., & Gupta, S. K. (2019). Response surface methodological (RSM) approach for optimizing the removal of trihalomethanes (THMs) and its precursor’s by surfactant modified magnetic nanoadsorbents (sMNP)-An endeavor to diminish probable cancer risk. Scientific Reports, 9(1), 1-11.
[32] Tang, S. Z., Wang, F. L., He, Y. L., Yu, Y., & Tong, Z. X. (2019). Parametric optimization of H-type finned tube with longitudinal vortex generators by response surface model and genetic algorithm. Applied Energy, 239, 908-918.
[33] Chavan, V., & Arakerimath, R. R. (2016). CFD Based Heat Transfer analysis of various Wavy Fin-and-Tube Heat Exchanger. International Journal of Current Engineering and Technology, (5), 258-261.
[34] Yin, J. M., Bullard, C. W., & Hrnjak, P. S. (2001). R-744 gas cooler model development and validation. International Journal of Refrigeration, 24(7), 692-701.
[35] Erek, A., Özerdem, B., Bilir, L., & Ilken, Z. (2005). Effect of geometrical parameters on heat transfer and pressure drop characteristics of plate fin and tube heat exchangers. Applied Thermal Engineering, 25(14-15), 2421-2431.
[36] Bhuiyan, A. A., Amin, M. R., Naser, J., & Islam, A. K. M. (2015). Effects of geometric parameters for wavy finned-tube heat exchanger in turbulent flow: a CFD modeling. Frontiers in Heat and Mass Transfer (FHMT), 6(1).
[37] Romero-Méndez, R., Sen, M., Yang, K. T., & McClain, R. (2000). Effect of fin spacing on convection in a plate fin and tube heat exchanger. International Journal of Heat and Mass Transfer, 43(1), 39-51.
[38] Torikoshi, K., & Xi, G. N. (1995). A Numerical Steady of Flow and Thermal Fields in Finned Tube Heat Exchangers (Effect of the Tube Diameter). IMECE Proceedings of the ASME Heat Transfer Division, 317(1), 453-457.
[39] Tutar, M., & Akkoca, A. (2004). Numerical analysis of fluid flow and heat transfer characteristics in three-dimensional plate fin-and-tube heat exchangers. Numerical Heat Transfer, Part A: Applications, 46(3), 301-321.
[40] Watel, B., Harmand, S., & Desmet, B. (1999). Influence of flow velocity and fin spacing on the forced convective heat transfer from an annular-finned tube. JSME International Journal Series B Fluids and Thermal Engineering, 42(1), 56-64.
[41] Sparrow, E. M., & Samie, F. (1985). Heat transfer and pressure drop results for one-and two-row arrays of finned tubes. International Journal of Heat and Mass Transfer, 28(12), 2247-2259.
[42] Nir, A. (1991). Heat transfer and friction factor correlations for crossflow over staggered finned tube banks. Heat Transfer Engineering, 12(1), 43-58.