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RESEARCH PAPERS: Micro/Nanoscale Heat Transfer

A Theory of Film Condensation in Horizontal Noncircular Section Microchannels

[+] Author and Article Information
Hua Sheng Wang

Department of Engineering, Queen Mary, University of London, London E1 4NS, United Kingdomh.s.wang@qmul.ac.uk

John W. Rose

Department of Engineering, Queen Mary, University of London, London E1 4NS, United Kingdomj.w.rose@qmul.ac.uk

J. Heat Transfer 127(10), 1096-1105 (Jun 16, 2005) (10 pages) doi:10.1115/1.2033905 History: Received September 14, 2002; Revised June 16, 2005

The paper presents a theoretical model to predict film condensation heat transfer from a vapor flowing in horizontal square and equilateral triangular section minichannels or microchannels. The model is based on fundamental analysis which assumes laminar condensate flow on the channel walls and takes account of surface tension, interfacial shear stress, and gravity. Results are given for channel sizes (side of square or triangle) in the range of 0.5–5 mm and for refrigerants R134a, R22, and R410A. The cases considered here are where the channel wall temperature is uniform and the vapor is saturated at the inlet. The general behavior of the condensate flow pattern (spanwise and streamwise profiles of the condensate film), as well as streamwise variation of local mean (over section perimeter) heat-transfer coefficient and vapor mass quality, are qualitatively in accord with expectations on physical grounds. The magnitudes of the calculated heat-transfer coefficients are in general agreement with experimental data for similar, but nonidentical, channel geometry and flow parameters.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Physical model and coordinates for horizontal microchannels

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Figure 2

Condensate film profiles along channel surface at different distances. Effects of interfacial shear stress, surface tension and gravity included. R134a, b=1.0mm, Ts=50°C, ΔT=6K, G=500kg∕m2s.

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Figure 3

Local film thickness along channel surface at different distances. Effects of interfacial shear stress, surface tension and gravity included.

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Figure 4

Local heat-transfer coefficient along channel surface at different distances

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Figure 5

Variation of mean (over perimeter of channel) heat-transfer coefficient with distance

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Figure 6

Variation of mean (over perimeter of channel) heat-transfer coefficient with distance for several fluid mass velocities

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Figure 7

Variation of vapor mass quality with distance along channels and mass velocity

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Figure 8

Effect of orientation for triangular channel. Solid line: inverted triangle; dashed line: upright triangle.

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Figure 9

Effect of vapor-to-surface temperature difference

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Figure 10

Effect of channel size for square section channels

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Figure 11

Effects of fluid properties

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Figure 12

Data of Koyama (Ref. 23) for condensation of R134a in tube B (see Fig. 1). PR is refrigerant pressure, TR is refrigerant temperature, TRmix is refrigerant temperature at mixing chamber, Twi is inside wall temperature, TS is coolant temperature, q is heat flux, α is heat-transfer coefficient, χ is refrigerant vapor mass quality.

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Figure 13

Tube B used by Koyama et el. (Ref. 23). Hydraulic diameter 0.81 mm.

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