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Abstract
The heat transfer and fluid flow characteristics of a new type of fin with built-in interrupted delta winglets is studied in this paper by three-dimensional numerical simulation. In order to ensure reliability of numerical model, plate fin with common-flow-up delta winglets is firstly simulated. The comparison of numerical and experimental results shows a maximum deviation of 11.4% within the entire range of Reynolds number. The computational results show that heat transfer capacity and overall performance increase by 35–60% and 19–64%, respectively. The flow field visualization shows that the interrupted delta winglets can produce longitudinal vortices at the rear of delta winglets and reduce the wake zone behind the tube, so the proposed fin can enhance heat transfer accompanied by low pressure loss. The field synergy theory and entransy dissipation extremum principle are employed on analyzing the mechanism of heat transfer enhancement. The results indicate that enhancement heat transfer mechanism of interrupted delta winglets can be explained as the result of the decrease of synergy angle and reduction of the entransy dissipation.
NOMENCLATURE
| A | = | area, m2 |
| Ac | = | area of minimum section, m2 |
| A0 | = | area of fin and tube surface, m2 |
| cp | = | specific heat capacity, J/(kg-K) |
| Dc | = | tube outside diameter, mm |
| Dh | = | hydraulic diameter, mm |
| f | = | friction factor |
| h | = | heat transfer coefficient, W/(m2-K) |
| k | = | turbulence kinetic energy, m2/s2 |
| j | = | Colbum j factor |
| L | = | depth of the heat exchanger in air flow direction, m |
| Nu | = | Nusselt number |
| Δp | = | pressure drop, Pa |
| Pr | = | Prandtl number |
| Q | = | heat transfer rate, W |
| ReDc | = | Reynolds number |
| Rh | = | equivalent thermal resistance, (K-m2)/W |
| S | = | source term |
| T | = | temperature, K |
| ΔT | = | temperature gradient |
| uc | = | minimum section average velocity, m/s |
| U | = | velocity vector |
| V | = | volume, m3 |
| y+ | = | y plus (nondimensional wall distance) |
Greek Symbols
| β | = | field synergy angle, degrees |
| Γ | = | diffusion coefficient, m2/s |
| ϵ | = | dissipation rate, m2/s3 |
| η | = | dynamic viscosity, kg/(m-s) |
| ηt | = | turbulent viscosity, kg/(m-s) |
| λ | = | thermal conductivity, W/(m2-K) |
| ρ | = | density, kg/m3 |
| φ | = | dependent variable |
| σ | = | turbulent Prandtl number |
Subscripts
| in | = | inlet |
| out | = | outlet |
| w | = | wall |
Additional information
Notes on contributors
Xue-Hong Wu
Xue-Hong Wu is an associate professor at the School of Energy and Power Engineering, Zhengzhou University of Light Industry. He obtained his Ph.D. degree from Xi'an Jiaotong University in 2009. His main research interests include enhanced heat transfer and the application of the proper orthogonal decomposition and the meshless method in the fluid flow and heat transfer area.
Pei Yuan
Pei Yuan is a lecturer at the School of Energy and Power Engineering, Zhengzhou University of Light Industry. He obtained his Ph.D. degree from Xi'an Jiaotong University in 2013. His main research interests include enhanced heat transfer and numerical simulation.
Zhi-Ming Luo
Zhi-Ming Luo is a graduate student at the School of Energy and Power Engineering, Zhengzhou University of Light Industry. His main research interests include enhanced heat transfer.
Li-Xun Wang
Li-Xun Wang is a graduate student at the School of Energy and Power Engineering, Zhengzhou University of Light Industry. His main research interests include enhanced heat transfer.
Yan-Li Lu
Yan-Li Lu is a professor at the School of Energy and Power Engineering, Zhengzhou University of Light Industry. He obtained his Ph.D. degree from Xi'an Jiaotong University in 2008. His main research interests include enhanced heat transfer.