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RESEARCH PAPERS: Evaporation, Boiling, and Condensation

# Film Condensation of R-134a on Tube Arrays With Plain and Enhanced Surfaces: Part I—Experimental Heat Transfer Coefficients

[+] 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), 21-32 (Jul 12, 2005) (12 pages) doi:10.1115/1.2130400 History: Received November 05, 2004; Revised July 12, 2005

## Abstract

The aim of the present investigation was to study the effect of condensate inundation on the thermal performance of a vertical array of horizontal tubes with plain and enhanced surfaces. Refrigerant R-134a was condensed at a saturation temperature of $304K$ on tube arrays with up to ten tubes at pitches of $25.5,28.6,and44.5mm$. Notably, local condensing heat transfer coefficients were measured at the midpoint of each tube, as opposed to mean values. Four commercially available copper tubes with a nominal diameter of $19.05mm$$(0.75in.)$ were tested: a plain tube, a $26fpi∕1024fpm$ low finned tube, and two tubes, with three-dimensional (3D) enhanced surface structures. At low liquid inundation rates, the tubes with 3D enhanced surface structures significantly outperformed the low finned tube. Increasing liquid inundation deteriorated the thermal performance of the 3D enhanced tubes, whereas it had nearly no affect on the low finned tube, resulting in a higher heat transfer coefficients for the low finned tube at high liquid film Reynolds numbers. All the tests were performed with minimal vapor shear.

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## Figures

Figure 1

Schematic of the experimental apparatus

Figure 2

Test section

Figure 3

Schematic of the instrumentation setup for a pair of tubes to measure the temperature profile of the water flowing inside

Figure 4

Tubes tested in this study

Figure 5

Condensation on the top tube without liquid overfeed

Figure 6

Comparison of single low finned tube data with different correlations (e=mean relative error)

Figure 7

Comparison of single tube performance without liquid overfeed

Figure 8

Measurements with liquid inundation on the Turbo-CSL tube with a tube pitch of 25.5mm at a nominal heat flux of 40kW∕m2

Figure 9

Comparison of the four types of tubes with tube pitch of 25.5mm at a nominal heat flux of 40kW∕m2 (12kW∕m2 for the plain tube)

Figure 10

Tube spacing influence of the Turbo-CSL tube at a nominal heat flux of 40kW∕m2 over a limited heat flux range

Figure 11

Tube spacing influence of the Gewa-C tube at a nominal heat flux of 40kW∕m2 over a limited heat flux range

Figure 12

Tube spacing influence of the Turbo-Chil tube at a nominal heat flux of 40kW∕m2 over a limited heat flux range

Figure 13

Tube spacing influence of plain tube at a nominal heat flux of 12kW∕m2 on the top three tubes in the array

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