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TECHNICAL BRIEFS

Polymeric Absorbers for Flat-Plate Collectors: Can Venting Provide Adequate Overheat Protection?

[+] Author and Article Information
Meghan Kearney, Susan Mantell

 Department of Mechanical Engineering, 111 Church Street, S.E., Minneapolis, Minnesota 55455

Jane Davidson1

 Department of Mechanical Engineering, 111 Church Street, S.E., Minneapolis, Minnesota 55455

1

Fellow ASME, Corresponding author; e-mail: jhd@me.umn.edu

J. Sol. Energy Eng 127(3), 421-424 (Nov 01, 2004) (4 pages) doi:10.1115/1.1979518 History: Received August 05, 2004; Revised November 01, 2004

Venting and evaporative cooling are modeled as possible techniques for protecting polymer absorbers in single-glazed, flat-plate solar collectors from exceeding the material temperature limit during dry stagnation. Four venting options are considered: (I) venting above the absorber plate, (II) venting below, (III) dual venting, and (IV) venting with evaporative cooling. Results indicate that in hot, sunny conditions, venting may not provide adequate cooling to lower the absorber temperature to the relative thermal index of the polymeric materials currently in use or under consideration for this application. Venting combined with evaporative cooling from a wetted pad directly beneath the absorber plate is identified as a potential method of overheat protection in hot, dry climates.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Sketch of a flat-plate solar collector with vents above and beneath the absorber plate (case III). The other cases considered are: case I with the upper vent open and the lower vent filled with insulation; case II with the lower vent used and the upper vent closed; case IV with the lower vent used in conjunction with an absorbent pad adjacent to the absorber plate. In cases II and IV, the upper vent space shown is closed and serves as the gap between the absorber and glazing.

Grahic Jump Location
Figure 2

Plot of the predicted absorber plate temperature versus insolation for two baseline collectors with and without selective absorbers and for venting cases I–IV. The dashed curves indicate cases with either no vent channel or with the vent channel present but closed. The solid curves represent the venting cases.

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