Role of transverse dimples in thermal-hydraulic performance of dimpled enhanced tubes

Rizwan Sabir, Muhammad Mahabat Khan, Muhammad Imran*, Nadeem Ahmed Sheikh, M. Irfan

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

This study numerically investigates the effects of transverse dimples in thermal and hydraulic performance improvement of Teardrop, Ellipsoidal-0o and Ellipsoidal-45o dimpled tubes under constant surface heat flux (q′′ = 10kW/m2) for turbulent Reynolds numbers (5000 ≤ Re ≤ 40,000). The number of dimples in the transverse direction (Star) are varied from 4 to 8 while maintaining the tube length to pitch (spacing between successive dimples) of 10 for each tube configuration. It is observed from Performance Evaluation Criteria (PEC) that Ellipsoidal-45o-Star 6 dimpled tube (Tube 7), as compared to the smooth tube, enhances the performance by 88.2% at Re = 5000 however, it reduces to 23.9% at Re = 20,000 and becomes negligible at Re = 40,000. The Ellipsoidal-45o dimples generate a non-symmetric wake and create a flow path between downstream dimples. As Star increases the flow momentum increases and a swirl flow pattern is generated and consequently enhances fluid-dimple interaction at low turbulent Re. On the contrary, Teardrop-Star 6 (Tube 2) and Ellipsoidal-0o-Star 6 (Tube 5) perform better at 20000 ≤ Re ≤ 40,000. Tube 5 produces distinct flow streams and enhances the fluid-surfaces interactions at higher Re. Therefore, it is recommended for high turbulent Re.

Original languageEnglish
Article number106435
Pages (from-to)1-12
Number of pages12
JournalInternational Communications in Heat and Mass Transfer
Volume139
Early online date11 Oct 2022
DOIs
Publication statusE-pub ahead of print - 11 Oct 2022

Keywords

  • Dimple tube
  • Fluid flow
  • Friction factor
  • Heat transfer augmentation
  • Star

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