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Research Papers: Heat Exchangers

Analysis of the Fin Performance of Offset Strip Fins Used in Plate-Fin Heat Exchangers

[+] Author and Article Information
Yujie Yang

State Key Laboratory of Power Engineering and
Multiphase Flow,
Department of Refrigeration and
Cryogenic Engineering,
School of Energy and Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: yyj_898@stu.xjtu.edu.cn

Yanzhong Li

State Key Laboratory of Power Engineering and
Multiphase Flow,
Department of Refrigeration and
Cryogenic Engineering,
School of Energy and Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: yzli-epe@mail.xjtu.edu.cn

Biao Si

Department of Refrigeration and
Cryogenic Engineering,
School of Energy and Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: si.biao@stu.xjtu.edu.cn

Jieyu Zheng

Department of Refrigeration and
Cryogenic Engineering,
School of Energy and Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: zjy.521331@stu.xjtu.edu.cn

Rui Kang

Department of Refrigeration and
Cryogenic Engineering,
School of Energy and Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: kangrui996996@stu.xjtu.edu.cn

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received August 11, 2015; final manuscript received May 5, 2016; published online June 7, 2016. Assoc. Editor: Danesh / D. K. Tafti.

J. Heat Transfer 138(10), 101801 (Jun 07, 2016) (9 pages) Paper No: HT-15-1540; doi: 10.1115/1.4033615 History: Received August 11, 2015; Revised May 05, 2016

As an important consideration in the design of plate-fin heat exchangers, the selection of plate-fin surfaces is associated with the estimation of the fin performance in many cases. The fin performance of offset strip fin (OSF) and plain fin is numerically investigated with well-validated 3D models in the present study. The comparative analysis shows that the conventional fin efficiency and fin effectiveness concepts provide an incomplete assessment of the fin performance of the fins, and lead to impractical suggestions of using OSF fin. Further investigation indicates that the idealization of uniform heat transfer coefficient over all the surfaces in fin channel, which runs through the conventional concepts, is untenable, and strongly restricts the fin performance analysis. An actual fin effectiveness is then proposed to measure the fin performance. It physically represents the ratio of the heat flux over the fin surfaces and that over the primary surfaces in the fin channel. With this method, the effects of the geometrical parameters of the OSF are discussed carefully. The results show that there exists a specific fin thickness-to-height ratio α and fin density γ, which contribute to the highest fin performance for a given mass flux, and the optimal γ (or α) increases (or decreases) as mass flux increases. The OSF fins with relatively large fin thickness-to-length ratio δ perform better in low Re region and the optimum δ decreases with the increasing Re number.

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References

Figures

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Fig. 1

The geometries of OSF fin and plain fin (a) offset strip fin and (b) plain fin

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Fig. 2

The computational domains for OSF fin and plain fin

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Fig. 3

Mesh generation in the computational domain (partial region)

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Fig. 4

Comparison of the numerical results and the experimental data for the plain fins

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Fig. 5

Comparison of the numerical results and the experimental data for the OSF fins

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Fig. 6

Behavior of the defined fin efficiency in terms of Re number for the plate fins

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Fig. 7

Behavior of the ideal fin efficiency in terms of Re number for the plate fins

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Fig. 8

The positions of the surfaces in the analysis of local data

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Fig. 9

Local dimensionless temperature difference on the secondary fin surface

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Fig. 10

Local heat transfer coefficient on the secondary fin surface

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Fig. 11

Behavior of conventional fin effectiveness in terms of Re number for the plate fins

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Fig. 12

Local dimensionless temperature difference over the heat transfer surfaces of OSF fin

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Fig. 13

Local dimensionless temperature difference over the heat transfer surfaces of plain fin

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Fig. 14

Local heat transfer coefficient over the heat transfer surfaces of OSF fin

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Fig. 15

Local heat transfer coefficient over the heat transfer surfaces of plain fin

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Fig. 16

Behavior of the actual fin effectiveness in terms of Reynolds number

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Fig. 17

The front-fin-end area Affe of OSF fins

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Fig. 18

εf,act versus γ with Affe/t2 as a parameter for OSF fins

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Fig. 19

εf,act versus γ with mass flux G as a parameter for OSF fins

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Fig. 20

Actual fin effectiveness of OSF fin in terms of fin thickness-to-length ratio

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