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ABSTRACT
The convective heat transfer and flow resistance properties of water flowing through a twisted trilobed tube (TTT) with Reynolds numbers that ranged from 10,000 to 40,000 were examined in this work. Specifically, we examined how the tip circle radius (r), straight length (l), transition radius (R), and twist pitch (S) influenced the heat transfer and flow resistance in the tube. Our results showed that the TTT had an average Nusselt number (Nu) that was 30% higher than that of a plain tube, while the friction coefficient (f) increased by 39%. We also presented temperature and velocity field distributions and explained the enhanced heat transfer process using the field synergy principle. Furthermore, we found that a larger tip circle radius (r) and straight length (l), as well as a smaller transition radius (R) and twist pitch (S), led to better overall heat transfer performance of the TTT. Among the different cases evaluated, Case 7 had the highest overall heat transfer performance with a PEC of 1.37. The unusual structure of the TTT caused a rotating motion, which resulted in secondary and spiral flows that increased the synergy through the velocity and temperature fields. Finally, our research found a correlation with the Nusselt number (Nu) as well as the friction coefficient (f).
Nomenclature
| Greek symbols | = |
|
| Cp | = | specific heat, J/(kg K) |
| Dh | = | hydraulic diameter, mm |
| D | = | diameter of the circle, mm |
| f | = | friction factor |
| Fc | = | field synergy number |
| G | = | mass flux, kg·m−2·s−1 |
| Gk | = | generation of turbulence kinetic energy, kg·m−1·s−3 |
| Gw | = | generation of specific dissipation rate, kg·m−3·s−2 |
| Gb | = | buoyancy term of turbulence kinetic energy, kg·m−1·s−3 |
| Gωb | = | buoyancy term of specific dissipation rate, kg·m−3·s−2 |
| h | = | heat transfer coefficient, W/(m2 K) |
| k | = | turbulent kinetic energy, m2·s−2 |
| l | = | straight length, mm |
| L | = | The effective length of the tested tube, mm |
| Nu | = | Nusselt number |
| S | = | twist pitch length, mm |
| St | = | twist pitch ratio |
| P | = | pressure, MPa |
| Pr | = | Prandtl number |
| Prt | = | Turbulent Prandtl number |
| r | = | tip circle radius, mm |
| R | = | transitional radius, mm |
| Re | = | Reynolds number |
| T | = | temperature, K |
| = | velocity vector, m·s−1 | |
| U | = | velocity component, m·s−1 |
| V | = | average velocity, m·s−1 |
| Yk | = | dissipation of turbulence kinetic energy, kg·m−1·s−3 |
| Yω | = | dissipation of specific dissipation rate, kg·m−3·s−2 |
| Гk | = | effective viscosity in the equation of k |
| Гω | = | effective viscosity in the equation of ω |
| ▽T | = | temperature gradient, K/m |
| Δp | = | pressure drop, MPa |
| W | = | The volume of computational zone m3 |
| λ | = | thermal conductivity, W/(m·K) |
| ρ | = | density, kg/m3 |
| μ | = | dynamics viscosity, kg/(m·s) |
| β | = | synergy angle, ° |
| ω | = | specific dissipation rate, s−1 |
| υ | = | kinematic viscosity, m2·s−1 |
| Subscripts | = |
|
| in | = | inlet zone |
| out | = | outlet zone |
| i | = | inscribed circle |
| c | = | circumscribed circle |
| w | = | wall |
| o | = | plain tube |
Disclosure statement
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Additional information
Funding
Notes on contributors
Kexin Liu
Kexin Liu is a PhD student in the School of Engineering Training Center, Northeast Electric Power University, Jilin, China. His research interests include advanced manufacturing technology, heat transfer enhancement and multiphase flow.
Xunjian Che
Xunjian Che is a lecturer in the School of Energy and Power Engineering, Northeast Electric Power University, Jilin, China. His research interests include advanced control technology of flow and heat transfer, control system development.
Qian Li
Qian Li is an Associate professor in the School of Energy and Power Engineering, Northeast Electric Power University, Jilin, China. His research interests include complex flow and heat transfer, simulation and design of heat exchanger.
Weihua Cai
Weihua Cai is a professor in the School of Energy and Power Engineering, Northeast Electric Power University, Jilin, China. His research interests include nuclear reactor thermal hydraulics, turbulent flow, natural gas and hydrogen liquefaction process.