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Research Papers: Evaporation, Boiling, and Condensation

Predicting Heat Transfer in Long R-134a Filled Thermosyphons

[+] Author and Article Information
M. H. M. Grooten

Department of Mechanical Engineering, Technische Universiteit Eindhoven, Postbus 513, 5600 MB Eindhoven, The Netherlandsc.w.m.v.d.geld@tue.nl

C. W. M. van der Geld

Department of Mechanical Engineering, Technische Universiteit Eindhoven, Postbus 513, 5600 MB Eindhoven, The Netherlands

J. Heat Transfer 131(5), 051501 (Mar 20, 2009) (9 pages) doi:10.1115/1.3000969 History: Received March 31, 2008; Revised September 16, 2008; Published March 20, 2009

When traditional air-to-air cooling is too voluminous, heat exchangers with long thermosyphons offer a good alternative. Experiments with a single thermosyphon with a large length-to-diameter ratio (188) and filled with R-134a are presented and analyzed. Saturation temperatures, filling ratios, and angles of inclination have been varied in wide ranges. A higher sensitivity of evaporation heat transfer coefficients on reduced pressure than in previous work has been found. Measurements revealed the effect of pressure or the saturation temperature on condensation heat transfer. The condensate film Reynolds number that marks a transition from one condensation heat transfer regime to another is found to depend on pressure. This effect was not accounted for by correlations from the literature. New correlations are presented to predict condensation and evaporation heat transfer rates.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 7

Measured heat transfer coefficient condenser side for various saturation temperatures, Fe=62%, and vertical orientation. Lines are given to guide the eye.

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Figure 8

Measured heat transfer coefficient evaporator side for various saturation temperatures, Fe=62%, and vertical orientation. Lines are given to guide the eye.

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Figure 9

Measured mean temperature differences between evaporator and condenser for various inclination angles, Fe=62%, and Tsat=20°C

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Figure 10

Measured heat transfer coefficient condenser side for various inclination angles, Fe=62%, and Tsat=20°C. Lines are given to guide the eye.

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Figure 11

Measured heat transfer coefficient evaporator side for various inclination angles, Fe=62%, and Tsat=20°C

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Figure 12

Comparison of measured and predicted heat transfer coefficient condenser sides for various models at various saturation temperatures, vertical orientation, and Fe=62%

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Figure 13

Film condensation heat transfer in a vertical thermosyphon, Fe=62%, vertical orientation, and accuracy of present correlation (Eq. 13)

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Figure 14

Condensation heat transfer versus film Reynolds number for various reduced pressures

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Figure 15

Comparison of measured and predicted heat transfer coefficient evaporator sides for various models at various saturation temperatures, vertical orientation, and Fe=62%

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Figure 16

Comparison of measured and predicted heat transfer coefficient evaporator sides with the present correlation (Eq. 18) at various saturation temperatures, vertical orientation, and Fe=62%. See Fig. 1 for the legend.

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Figure 1

Schematic view of a thermosyphon

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Figure 2

Schematic view of the experimental setup

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Figure 3

Typical histories of wall temperatures, Q=400 W for vertical orientation, Fe=62%

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Figure 4

Comparison of measured heat flow rates at evaporator and condenser at Fe=62%, vertical orientation, for various saturation temperatures, Aevap=0.0543 m2, and Acond=0.0656 m2

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Figure 5

Measured mean temperature differences between evaporator and condenser versus heat flow rate and evaporator heat flux for various saturation temperatures at Fe=62% and for vertical orientation. The evaporator heat flux scale is linear.

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Figure 6

Typical deviation in measurements of the saturation temperature with several methods, compared with the mean evaporator and condenser temperatures. Lines are given to guide the eye.

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