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Research Papers: Evaporation, Boiling, and Condensation

The Effect of the Angle of Inclination on the Operation Limiting Heat Flux of 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, Netherlands

C. W. M. van der Geld

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

J. Heat Transfer 132(5), 051501 (Mar 04, 2010) (5 pages) doi:10.1115/1.4000441 History: Received November 21, 2008; Revised September 18, 2009; Published March 04, 2010; Online March 04, 2010

When traditional air-to-air cooling is too voluminous, long thermosyphons may offer a way out. For safe operation of heat exchangers equipped with thermosyphons, the limiting heat flux qlim is an important design parameter. Some literatures are found to deal with the operation limiting heat flux of closed two-phase thermosyphons. However, R-134a filled thermosyphons with large length-to-diameter (188) are hardly investigated up to now. Extrapolation of existing correlations to predict qlim in this case results in large scatter. The effect of the angle of inclination on qlim has not been considered until now. Dedicated experiments with a single thermosyphon with a large length-to-diameter ratio (188) and filled with R-134a are presented and analyzed. Effects of saturation temperature, filling ratio, and angle of inclination β on the operational limiting heat flux have been investigated. The thermosyphon functions properly if β<83deg, and qlim is found to increase with increasing β. With decreasing saturation temperature, qlim increases. The filling ratio is found not to be crucial if it exceeds 25%. Correlations are presented to accurately predict the operation limiting heat flux for thermosyphons with a L/d ratio up to 188. Because of the accounting for the above new aspects, these correlations are also relevant for filling refrigerants other than R-134a.

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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic view of the experimental setup

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Figure 2

Temperature history at operating limit. Inset shows thermocouple positions.

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Figure 3

Temperature history at operating limit at large inclination and high temperatures (see Fig. 2 for thermocouple positions)

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Figure 4

Operating limit of the thermosyphon versus saturation temperature for various filling ratios Aevap=0.0543 m2. Evaporator heat flux scale is linear.

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Figure 5

Operating limit of the thermosyphon versus inclination angle for various filling ratios and saturation temperatures Aevap=0.0543 m2

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Figure 6

Proof of wetting of the adiabatic wall at inclination by a liquid film by drop impingement

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Figure 7

Predicted operation limiting heat flux by correlations from literature, β=0 deg

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