The effects of twisted strips with different length on heat transfer and pressure drop in concentric heat exchanger

Abstract

This study investigated the use of twisted strips as passive turbulators to improve heat transfer efficiency in concentric heat exchangers. In the experiments, four different lengths of twisted strips were designed (l = 0.25 m, 0.5 m, 0.75 m, and 1 m) and their performance was evaluated in a system with air and water fluids. The effects of twisted strips on heat transfer and pressure drops are investigated in both parallel and countercurrent flow patterns, and the results are analyzed in terms of Nusselt and Reynolds numbers. The results indicated that tubes using twisted strips achieved significant increases in the heat transfer coefficient compared to straight tubes. The highest increase in heat transfer performance reached 78% when the length of the twisted strip was l/L=1. The Nusselt number increased by a factor of 1.2 to 1.8, depending on the length of the twisted strips. The shortest strip length (l/L=0.25) resulted in the lowest heat transfer performance. However, these improvements were accompanied by significant increases in pressure drop; for full-length strips, the pressure drop increased by nearly 100%. The pressure drop increased slightly as the Reynolds number increased. The swirling flow generated by the twisted ribbons plays an important role in increasing the heat transfer. Despite the increases in pressure drops, the energy loss is negligible compared to the heat transfer gain achieved. In conclusion, the length ratio of the twisted strips significantly affects the thermal performance of the heat exchanger while increasing the pressure losses. These findings demonstrate the effectiveness of twisted strips as passive turbulators.

Keywords

• Twisted Strips
• Concentric Heat Exchanger
• Heat transfer
• Pressure Drop

References

1. H. Hamed, A. Mohammed, R. Khalefa, O. Habeeb, and M. Abdulqader, “The Effect of using Compound Techniques (Passive and Active) on the Double Pipe Heat Exchanger Performance,” Egypt. J. Chem., pp. 0–0, Mar. 2021, doi: 10.21608/ejchem.2021.54450.3134.
2. M. Sheikholeslami, M. Gorji-Bandpy, and D. D. Ganji, “Review of heat transfer enhancement methods: Focus on passive methods using swirl flow devices,” Renew. Sustain. Energy Rev., vol. 49, pp. 444–469, Sep. 2015, doi: 10.1016/j.rser.2015.04.113.
3. F. Seibold, P. Ligrani, and B. Weigand, “Flow and heat transfer in swirl tubes — A review,” Int. J. Heat Mass Transf., vol. 187, p. 122455, May 2022, doi: 10.1016/j.ijheatmasstransfer.2021.122455.
4. J. Chen et al., “Understanding the role of swirling flow in dry powder inhalers: Implications for design considerations and pulmonary delivery,” J. Control. Release, vol. 373, pp. 410–425, Sep. 2024, doi: 10.1016/j.jconrel.2024.07.034.
5. M. Hangi, A. Rahbari, X. Wang, and W. Lipiński, “Hydrothermal characteristics of fluid flow in a circular tube fitted with free rotating axial-turbine-type swirl generators: Design, swirl strength, and performance analyses,” Int. J. Therm. Sci., vol. 173, p. 107384, Mar. 2022, doi: 10.1016/j.ijthermalsci.2021.107384.
6. D. Wang, A. Khalatov, I. Borisov, E. Shi-Ju, and O. Stupak, “Swirling flow and heat transfer in a pipe: Decay and transition to axial flow,” Int. J. Heat Mass Transf., vol. 233, p. 125976, Nov. 2024, doi: 10.1016/j.ijheatmasstransfer.2024.125976.
7. L. Liu, J. Zhang, S. Liu, K. Wang, and H. Gu, “Decay law and swirl length of swirling gas-liquid flow in a vertical pipe,” Int. J. Multiph. Flow, vol. 137, p. 103570, Apr. 2021, doi: 10.1016/j.ijmultiphaseflow.2021.103570.
8. R. Babu., P. Kumar., S. Roy, and R. Ganesan, “A comprehensive review on compound heat transfer enhancement using passive techniques in a heat exchanger,” Mater. Today Proc., vol. 54, pp. 428–436, 2022, doi: 10.1016/j.matpr.2021.09.541.

9. R. Mashayekhi, A. H. Eisapour, M. Eisapour, P. Talebizadehsardari, and A. Rahbari, “Hydrothermal performance of twisted elliptical tube equipped with twisted tape insert,” Int. J. Therm. Sci., vol. 172, p. 107233, Feb. 2022, doi: 10.1016/j.ijthermalsci.2021.107233.
10. B. Kumar, A. K. Patil, S. Jain, and M. Kumar, “Effects of Double V Cuts in Perforated Twisted Tape Insert: An Experimental Study,” Heat Transf. Eng., vol. 41, no. 17, pp. 1473–1484, Sep. 2020, doi: 10.1080/01457632.2019.1649926.
11. Y. Hong, L. Zhao, Y. Huang, Q. Li, J. Jiang, and J. Du, “Turbulent thermal-hydraulic characteristics in a spiral corrugated waste heat recovery heat exchanger with perforated multiple twisted tapes,” Int. J. Therm. Sci., vol. 184, p. 108025, Feb. 2023, doi: 10.1016/j.ijthermalsci.2022.108025.
12. M. M. K. Bhuiya, M. M. Roshid, M. M. M. Talukder, M. G. Rasul, and P. Das, “Influence of perforated triple twisted tape on thermal performance characteristics of a tube heat exchanger,” Appl. Therm. Eng., vol. 167, p. 114769, Feb. 2020, doi: 10.1016/j.applthermaleng.2019.114769.
13. B. K. Dandoutiya and A. Kumar, “Study of thermal performance of double pipe heat exchanger using W-cut twisted tape,” Energy Sources, Part A Recover. Util. Environ. Eff., vol. 45, no. 2, pp. 5221–5238, Jun. 2023, doi: 10.1080/15567036.2023.2207497.
14. R. Behcet., A. Yakut., and Z. Argunhan., “The effect of rotary type turbulator placed in entrance of heat exchanger on heat transfer and frictional loss,” Energy Educ. Sci. Technol. Part A-Energy Sci. Res., vol. 28, no. 1, pp. 239–248, 2011.
15. Z. Argunhan and C. Yıldız, “The effects of swirl generator having wings with holes on heat transfer and pressure drop in tube heat exchanger.,” Pamukkale Univ. J. Eng. Sci., vol. 12, no. 2, pp. 217–223, 2011.
16. F. P. Incropera and D. P. Dewitt, Fundamentals of heat and mass transfer, 6th. ed. New York: J. Wiley & Sons, 2006.
17. V. I. Deev, V. S. Kharitonov, A. M. Baisov, and A. N. Churkin, “Heat transfer characteristics of water under supercritical conditions,” Int. J. Therm. Sci., vol. 171, p. 107238, Jan. 2022, doi: 10.1016/j.ijthermalsci.2021.107238.
18. G. Çakmak and C. Yıldız, “The influence of the injectors with swirling flow generating on the heat transfer in the concentric heat exchanger,” Int. Commun. Heat Mass Transf., vol. 34, no. 6, pp. 728–739, Jul. 2007, doi: 10.1016/j.icheatmasstransfer.2007.03.007.