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Research Papers: Evaporation, Boiling, and Condensation

Numerical Simulation of Condensation for R410A in Horizontal Round and Flattened Minichannels

[+] Author and Article Information
Wei Li

Fellow ASME
Department of Energy Engineering,
Zhejiang University,
Hangzhou 310027, China
e-mail: Weili96@zju.edu.cn

Jingzhi Zhang, Junye Li

Department of Energy Engineering,
Zhejiang University,
Hangzhou 310027, China

Guanghui Bai

Huadian Electric Power Research
Institute
Zhejiang, Hangzhou 310030, China

Jin-liang Xu

The Beijing Key Laboratory of Multiphase
Flow and Heat Transfer for
Low Grade Energy Utilization,
North China Electric Power University,
Beijing 102206, China

Terrence W. Simon

Mechanical Engineering Department,
University of Minnesota,
111 Church Street S.E.,
Minneapolis, MN 55455

Jin-jia Wei

State Key Laboratory of Multiphase
Flow in Power Engineering,
Xi'an Jiaotong University,
Xi'an, 710049, China

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received May 21, 2015; final manuscript received August 30, 2016; published online October 26, 2016. Assoc. Editor: Amitabh Narain.

J. Heat Transfer 139(2), 021501 (Oct 26, 2016) (9 pages) Paper No: HT-15-1352; doi: 10.1115/1.4034812 History: Received May 21, 2015; Revised August 30, 2016

Heat transfer characteristics for condensation for R410A inside horizontal round (dh = 3.78 mm) and flattened tubes (aspect ratio (AR) = 3.07, 4.23, and 5.39) with larger horizontal than vertical dimensions at a saturation temperature of 320 K are investigated numerically. The flattened tube has flat upper and lower walls and circular end walls. The heat and mass transfer model for condensation is verified by comparing numerical heat transfer coefficients of round tubes with experimental data and empirical correlations. Liquid–vapor interfaces and local heat transfer coefficients are also presented to give a better understanding of the condensation process inside these tubes. The results indicate that local heat transfer coefficients increase with increasing mass flux, vapor quality, and aspect ratio. The enhancement of heat transfer coefficients for flattened tubes is more pronounced at higher mass flux and vapor quality values (about 1.5 times the heat transfer coefficients for round tubes when G = 1061 kg m−2 s−1, x ≥ 0.8). Unlike in the round tubes, the liquid film in the flattened tube accumulates at the sides of the bottom surface and at the middle of the top surface of the channels when vapor quality is low. Peak values of liquid film thickness in flattened tubes are obtained around angles about the centroid θ of 70 deg and 117 deg, where θ = 0 deg is upward.

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References

Figures

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Fig. 1

Computational geometry and boundary conditions

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Fig. 2

Comparison between numerical void fraction and calculated values from models

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Fig. 3

Comparison with experimental results at x = 0.45

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Fig. 4

Comparison of numerical data with values computed from empirical correlations for heat transfer coefficients in round tubes at G ranging from 305 kg m−2 s−1 to1061 kg m−2 s−1 and x ranging from 0.41 to 0.98

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Fig. 5

Local heat transfer coefficients versus vapor quality for round and flattened tubes with G = 421, 738, and 1061 kg m−2 s−1, and Tsat = 320 K

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Fig. 6

Comparison of numerical heat transfer coefficients with values from empirical correlations using de and dh: (a) Cavallini et al. correlation [6] and (b) Thome et al. correlation [39].

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Fig. 7

Liquid–vapor interfaces for R410A inside round and flattened tubes with G = 421 and 1061 kg m−2 s−1: (a) round tube, (b) AR = 3.07, (c) AR = 4.23, and (d) AR = 5.39

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Fig. 8

The liquid film thickness along the axis direction inside flattened tubes when G = 421 and 1061 kg m−2 s−1: (a) G = 421 kg m−2 s−1, x = 0.5 and (b) G = 1061 kg m−2 s−1, x = 0.9

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Fig. 9

The liquid film thicknesses as a function of the angular coordinate for R410A inside round and flattened tubes when: (a) G = 1061 kg m−2 s1, x = 0.9 and (b) G = 421 kg m−2 s−1, x = 0.5

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Fig. 10

The local heat transfer coefficients against the angular coordinate with R410A when (a) G = 1061 kg m−2 s−1, x = 0.9 and (b) G = 421 kg m−2 s−1, x = 0.5

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