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RESEARCH PAPERS: Evaporation, Boiling, and Condensation

Film Condensation of R-134a on Tube Arrays With Plain and Enhanced Surfaces: Part II—Empirical Prediction of Inundation Effects

[+] Author and Article Information
D. Gstoehl

 Laboratory of Heat and Mass Transfer, Faculty of Engineering Sciences and Techniques, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland

J. R. Thome1

 Laboratory of Heat and Mass Transfer, Faculty of Engineering Sciences and Techniques, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerlandjohn.thome@epfl.ch

1

To whom correspondence should be addressed.

J. Heat Transfer 128(1), 33-43 (Jul 12, 2005) (11 pages) doi:10.1115/1.2130401 History: Received November 05, 2004; Revised July 12, 2005

New predictive methods for R-134a condensing on vertical arrays of horizontal tubes are proposed based on visual observations revealing that condensate is slung off the array of tubes sideways and significantly affects condensate inundation and thus the heat transfer process. For two types of three-dimensional (3D) enhanced tubes, the Turbo-CSL and the Gewa-C, the local heat flux is correlated as a function of condensation temperature difference, the film Reynolds number, the tube spacing, and liquid slinging effect. The measured heat transfer data of the plain tube were well described by an existing asymptotic model based on heat transfer coefficients for the laminar wavy flow and turbulent flow regimes or, alternatively, by a new model proposed here based on liquid slinging. For the 26fpi low finned tube, the effect of inundation was found to be negligible and single-tube methods were found to be adequate.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Ideal flow (left) and liquid “slinging” (right)

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Figure 2

Prediction of heat transfer coefficient of the 3D enhanced tubes at a tube pitch of 25.5mm (second method)

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Figure 3

Schematic of condensate leaving the tube sideways

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Figure 4

Prediction of heat transfer coefficients of the 3D enhanced tubes (first method)

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Figure 5

Tube row effect for the plain tube at a tube pitch of 25.5mm at a nominal heat flux of 6 and 20kW∕m2

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Figure 6

Local heat transfer coefficients on the top three plain tubes in the array. Comparison with correlations for the wavy and turbulent flow regimes on a vertical plate.

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Figure 7

Prediction of heat transfer coefficients of the plain tubes (asymptotic model)

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Figure 8

Prediction of heat transfer coefficients of the plain tubes (with slinging)

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