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Research Papers: Evaporation, Boiling, and Condensation

Enhanced Condensation of Ethylene Glycol on Single Pin-Fin Tubes: Effect of Pin Geometry

[+] Author and Article Information
Hafiz Muhammad Ali, Adrian Briggs

 School of Engineering and Materials Science, Queen Mary, University of London, Mile End Road, London E1 4NS, UKa.briggs@qmul.ac.uk

Throughout this paper enhancement ratio is defined as the heat-transfer coefficient of the enhanced tube, based on the pin- or fin-root diameter, divided by that of a plain tube with diameter equal to the root diameter of the enhanced tube and at the same vapor-side temperature difference.

J. Heat Transfer 134(1), 011503 (Nov 18, 2011) (8 pages) doi:10.1115/1.4004714 History: Received November 23, 2010; Revised July 14, 2011; Published November 18, 2011; Online November 18, 2011

This paper presents a fundamental study into the underlying mechanisms influencing heat transfer during condensation on enhanced surfaces. New experimental data are reported for condensation of ethylene glycol at near atmospheric pressure and low velocity on 11 different 3-dimensional pin-fin tubes tested individually. Enhancements of the vapor-side, heat-transfer coefficients were found between 3 and 5.5 when compared to a plain tube at the same vapor-side temperature difference. Heat-transfer enhancement was found to be strongly dependent on the active surface area of the tubes, i.e., on the surface area of the parts of the tube and pin surface not covered by condensate retained by surface tension. For all the tubes, vapor-side, heat-transfer enhancements were found to be approximately twice the corresponding active-area enhancements. The best performing pin-fin tube gave a heat-transfer enhancement of 5.5; 17% higher than obtained from “optimised” two-dimensional fin-tubes reported in the literature and about 24% higher than the “equivalent” two-dimensional integral-fin tube (i.e., with the same fin-root diameter, longitudinal fin spacing and thickness, and fin height). The effects of surface area and surface tension induced enhancement and retention are discussed in the light of the new data and those of previous investigations.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Liquid “flooding” on an integral fin tube (after Briggs [13])

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Figure 2

Schematic of idealised “pin-fin” tube

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Figure 3

Experimental apparatus

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Figure 4

Coolant-side correlation from instrumented plain tube

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Figure 5

Variation of heat flux with vapor-side temperature difference for ethylene glycol

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Figure 6

Dependence of heat transfer enhancement ratio on pin height

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Figure 7

Dependence of heat-transfer enhancement ratio on circumferential pin spacing and thickness

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Figure 8

Variation of heat transfer enhancement ratio with unflooded-area enhancement

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