## Abstract

Numerical simulations were performed with the open-source CFD software OpenFOAM to investigate the ability of several configurations of short-length twisted tube geometries with non-circular cross section connected to tubes with circular cross section to induce a swirling flow. The heat transfer and the pressure drop linked to the generated swirling flow are also calculated. The swirling flow is modeled using a k-ω SST turbulence model with a low-Reynolds approach. It is shown that a short-length twisted tube with an elliptical cross section (STE) is able to generate a swirling flow, but its intensity greatly depends on its twist pitch and its aspect ratio. The lower the aspect ratio, the higher the swirl intensity. For a Reynolds number ranging from 10,000 to 100,000, the results reveal that compared to a plain tube, the STE with the lowest aspect ratio achieves enhancing the heat transfer from 22 to 90% at the cost of an increased pressure drop of, respectively, 63 and 129%. The second part of the study is focused on a short-length twisted tube with a three-lobed cross section, and the results reveal that the generated swirling flow is even more intense than with the STE and that the heat transfer enhancement goes from 30 to 105% at the cost of an increased pressure drop from 137 to 180%.

Original language | English |
---|---|

Pages (from-to) | 1555-1568 |

Number of pages | 14 |

Journal | Journal of Thermal Analysis and Calorimetry |

Volume | 140 |

Issue number | 3 |

DOIs | |

Publication status | Published - 1 May 2020 |

### Bibliographical note

Funding Information:The authors would like to thank the financial support of the Association Nationale Recherche Technologie (ANRT) through the CIFRE Grant No. 2017/1437. a Major axis of the ellipse, m A Wetted area, m 2 b Minor axis of the ellipse, m c Aspect ratio of the ellipse, dimensionless c p Specific heat capacity, J kg −1 K −1 C f Skin friction coefficient, dimensionless Δ p Pressure drop, Pa D h Hydraulic diameter, m e Quantity to evaluate for the GCI f Friction factor coefficient, dimensionless GCI Grid convergence index h Heat transfer coefficient, W m −2 K −1 I Turbulence intensity, dimensionless k Turbulent kinetic energy, J kg −1 l Turbulent mixing length, m L Total length of the tested tube, m m Mass flow rate, kg s −1 Nu Nusselt number, dimensionless P Twist pitch, m r Refinement ratio, dimensionless Re Reynolds number, dimensionless S Swirl number, dimensionless T Temperature, K U Fluid velocity, m s −1 Q Heat flux, W z Axial position, m z * Dimensionless axial position (z D h −1 ) z 1 * Downstream dimensionless axial position z * = 24 α Order of accuracy for the GCI, dimensionless λ Thermal conductivity, W m −1 K −1 μ Dynamic viscosity, Pa.s ρ Fluid density, kg m −3 τ w Wall shear stress, Pa ω Turbulent kinetic energy dissipation rate, s −1

Publisher Copyright:

© 2019, Akadémiai Kiadó, Budapest, Hungary.

## Other keywords

- CFD
- Decaying swirling flow
- Elliptical
- Heat transfer
- Three-lobed
- Twisted tubes