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Research Papers: Evaporation, Boiling, and Condensation

Convective Condensation Inside Horizontal Smooth and Microfin Tubes

[+] Author and Article Information
Zan Wu

Department of Energy Sciences,
Lund University,
Box 118,
Lund SE-22100, Sweden
Department of Energy Engineering,
Zhejiang University,
Hangzhou 310027, China

Bengt Sundén

Department of Energy Sciences,
Lund University,
Box 118,
Lund SE-22100, Sweden
e-mail: bengt.sunden@energy.lth.se

Lei Wang

Department of Energy Sciences,
Lund University,
Box 118
Lund SE-22100, Sweden

Wei Li

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

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received October 26, 2012; final manuscript received December 19, 2013; published online March 6, 2014. Assoc. Editor: W. Q. Tao.

J. Heat Transfer 136(5), 051504 (Mar 06, 2014) (11 pages) Paper No: HT-12-1591; doi: 10.1115/1.4026370 History: Received October 26, 2012; Revised December 19, 2013

An experimental investigation was performed for convective condensation of R410A inside one smooth tube (3.78 mm, inner diameter) and six microfin tubes (4.54, 4.6 and 8.98 mm, fin root diameter) of different geometries for mass fluxes ranging from 99 to 603 kg m−2s−1. The experimental data were analyzed with updated flow pattern maps and evaluated with existing correlations. The heat transfer coefficient in the microfin tubes decreases at first and then increases or flattens out gradually as mass flux decreases. This obvious nonmonotonic heat transfer coefficient-mass flux relation may be explained by the complex interactions between the microfins and the fluid, mainly by surface tension effects. The heat transfer enhancement mechanism in microfin tubes is mainly due to the surface area increase at large mass fluxes, while liquid drainage by surface tension and interfacial turbulence enhance heat transfer greatly at low mass fluxes.

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Figures

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Fig. 1

Microfin surface geometry and cross-sectional profile of the microfin tube: (a) geometric parameters of the microfin surface and (b) cross-sectional profile of the microfin tube

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Fig. 2

Schematic drawings of (a): test rig and (b): test section

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Fig. 3

Flow pattern maps for R410A in horizontal smooth tubes and updated for use in microfin tubes at Tsat = 320 K: (a) the updated El Hajal et al. map [26] at di = 3.78, 4.60, and 8.98 mm and (b) the updated Cavallini et al. map [27] at di = 4.60 mm

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Fig. 4

Condensation (a) frictional pressure drop and evaluated by the Gronnerud correlation [29] and (b) heat transfer coefficient and evaluated by the Cavallini et al. correlation [27] in the smooth tube with 3.78 mm ID, at Tsat = 320 K, with inlet and outlet vapor qualities of 0.8 and 0.1, respectively

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Fig. 5

Condensation frictional pressure drop in microfin tubes: (a) experimental data and (b) comparison of experimental data and predicted values by existing correlations

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Fig. 6

Condensation heat transfer coefficient versus mass flux in microfin tubes: (a) experimental heat transfer data and (b) comparison of experimental data and predicted values by existing correlations, with inlet and outlet vapor qualities of 0.8 and 0.1, respectively

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Fig. 7

Heat transfer comparisons of Tube 1, Tube 4, Tube 6 with Huang et al. [14] (di = 4.6 mm, ns = 40, α = 40 deg, β = 18 deg, e = 0.14 mm), Jung et al. [8] (di = 8.92 mm, ns = 60, α = 53 deg, β = 18 deg, e = 0.2 mm), Cavallini et al. [37] (di = 8.15 mm, ns = 60, α = 43 deg, β = 13 deg, e = 0.23 mm) and Kim and Shin [38] (di = 8.9 mm, ns = 60, α = 53 deg, β = 18 deg, e = 0.2 mm)

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Fig. 8

The ratio hMF/(hS*A/Ani) versus mass flux for both R22 [19] and R410A condensation inside the tested microfin tubes

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