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RESEARCH PAPERS

Thermal Design of Compound Parabolic Concentrating Solar-Energy Collectors

[+] Author and Article Information
D. E. Prapas, B. Norton, S. D. Probert

Solar Energy Technology Center, School of Mechanical Engineering, Cranfield Institute of Technology, Bedford MK43 0AL, United Kingdom

J. Sol. Energy Eng 109(2), 161-168 (May 01, 1987) (8 pages) doi:10.1115/1.3268194 History: Received August 01, 1985; Online November 11, 2009

Abstract

A theoretical analysis of the heat exchanges in a Compound Parabolic Concentrator solar energy collector is presented. The absorber configuration considered is that of a tube (with or without a spectrally-selective surface) either directly exposed or enclosed within one or two glass envelopes. The annular cavity formed between the tube and the surrounding envelope can be either air-filled or evacuated. The optimal annular gap, which leads to the best overall collector efficiency, has been predicted for the nonevacuated arrangement. It was found to be approximately 5 mm for the considered geometry. This is about half that recommended by Rabl and Ratzel and gives a 3 percent better overall collector efficiency than obtained with their design. The evacuation of the annular cavity or the application of a selective surface, separately employed, are demonstrated to yield improvements of the same order. It was necessary, for the particular solar radiation data used, both to evacuate the cavity and apply a selective surface if receiver temperatures exceeding 140°C are required. The comparative performances of different CPC designs have also been considered. The theoretical predictions were compared with experimental results and adequate corroboration was obtained.

Copyright © 1987 by ASME
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