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Simultaneous Effect of Wavy Tube and Twisted Tape on Thermal Performance of a Heat Exchanger Pipe

Fazel, Zaynab | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: English
  3. Document No: 57038 (58)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Kazemzadeh Hannani, Siamak; Sadr Hosseini, Hani
  7. Abstract:
  8. The current thesis presents a numerical investigation on turbulent hydrothermal and thermodynamic characteristics in a wavy passage equipped with twisted tape. The working fluid is water and passage walls are kept under constant wall temperature. The effect of twist angle (TA=90° and 180°), inclination angle (IA=15° and IA=30° )and Reynolds number (Re=2500, 4500, 6500, 8500 and 10500 ) on velocity fields and streamlines, temperature contours, Nusselt number, friction factor, turbulent kinetic energy (TKE), thermal performance factor (TPF) , energy efficiency factor (EFF), entropy generation, exergy destruction and second law efficiency are evaluated. More uniform temperature and velocity fields can be found as both wavy passage and twisted tape are simultaneously applied. Both heat transfer rate and pumping power rise with increasing Reynolds number, twist and inclination angles. Results reveal that the twisted tape plays more remarkable role on Nusselt number and friction factor at lower inclination angle. The best value of TPF is 1.42, detected at Re=2500, IA=15° and TA=180°. Moreover, the TPF profiles become approximately monotonous as Reynolds number exceeds 5000. The proposed configuration can promote thermal energy transfer up to 27% compared to a plain one under similar pumping power condition. Along all considered cases, those of empty wavy passage with IA=30° at Re=6500, 8500 and 10500 provide negative values of energy efficiency factor (FEE), referring to inefficient cases from energy viewpoint. The contribution of wavy passage and twisted tape on heat transfer enhancement is individually assessed and it is found that the best value of twisted tape involvement on enhanced heat transfer is about 81%, found at Re=4500, IA=15° and TA=180°. From thermodynamics viewpoint, there exists a critical Reynolds number for each passage in which the entropy generation rate and thus exergy destruction profiles have maximum value. In addition, the second law efficiency values improve as inclination and twist angles increase. The findings of present study prove that the idea of inserting twisted tape in wavy tube can improve thermal performance of double-passage heat exchangers and thus may play an important role in various fields such as technological processes, energy, oil refining, manufacturing, transportation, air conditioning, cryogenic and recovery systems.
  9. Keywords:
  10. Heat Transfer ; Pressure Drop ; Twisted Tapes ; Wavy Tube ; Double Pipe Heat Exchanger ; Heat Exchangers ; Thermal Performance

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