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Research Papers: Heat Transfer Enhancement

# Numerical Study of Flow and Heat Transfer Enhancement by Using Delta Winglets in a Triangular Wavy Fin-and-Tube Heat Exchanger

[+] Author and Article Information
Liting Tian, Pan Chu, Wenquan Tao

State Key Laboratory of Multiphase Flow in Power Engineering, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China

Yaling He1

State Key Laboratory of Multiphase Flow in Power Engineering, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, Chinayalinghe@mail.xjtu.edu.cn

1

Corresponding author.

J. Heat Transfer 131(9), 091901 (Jun 22, 2009) (8 pages) doi:10.1115/1.3139106 History: Received April 22, 2008; Revised April 15, 2009; Published June 22, 2009

## Abstract

In this paper, three-dimensional numerical simulations with renormalization-group (RNG) $k-ε$ model are performed for the air-side heat transfer and fluid flow characteristics of wavy fin-and-tube heat exchanger with delta winglet vortex generators. The Reynolds number based on the tube outside diameter varies from 500 to 5000. The effects of different geometrical parameters with varying attack angle of delta winglet ($β=30 deg$, $β=45 deg$, and $β=60 deg$), tube row number (2–4), and wavy angle of the fin $(θ=0–20 deg)$ are examined. The numerical results show that each delta winglet generates a downstream main vortex and a corner vortex. The longitudinal vortices are disrupted by the downstream wavy trough and only propagate a short distance along the main flow direction but the vortices greatly enhance the heat transfer in the wake region behind the tube. Nusselt number and friction factor both increase with the increase in the attack angle $β$, and the case of $β=30 deg$ has the maximum value of $j/f$. The effects of the tube row number on Nusselt number and friction factor are very small, and the heat transfer and fluid flow become fully developed very quickly. The case of $θ=5 deg$ has the minimum value of Nusselt number, while friction factor always increases with the increase in wavy angle. The application of delta winglet enhances the heat transfer performance of the wavy fin-and-tube heat exchanger with modest pressure drop penalty.

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## Figures

Figure 1

Physical model and relevant geometrical parameters of the wavy fin-and-tube heat exchanger with delta winglets

Figure 2

Grid system around the delta winglet and tube

Figure 3

Validation of numerical models with experimental results

Figure 4

Secondary velocity vectors at the cross section of x=21 mm for ReDc=3000

Figure 5

Distribution of local average pressure along the streamwise direction for ReDc=3000

Figure 6

Distribution of circulation of flow cross section along the streamwise direction for ReDc=3000

Figure 7

Dimensionless temperature distribution on the bottom fin surface, (Tf−Tin)/(Tw−Tin)

Figure 8

Distribution of spanwise averaged local heat transfer coefficient along the streamwise direction for ReDc=3000

Figure 9

Effects of attack angle on Nusselt number and friction factor

Figure 10

Area goodness and volume goodness factors at different attack angles

Figure 11

Effect of tube row number on Nusselt number and friction factor

Figure 12

Area goodness and volume goodness factors at different tube row numbers

Figure 13

Effect of wavy angle on Nusselt number and friction factor

Figure 14

Area goodness and volume goodness factors at different wavy angles

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