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Derivation of efficiency factors for uneven irradiation on a fin absorber

Författare:
Publiceringsår: 2004
Språk: Engelska
Sidor: 261-267
Publikation/Tidskrift/Serie: SOLAR ENERGY
Volym: 77
Nummer: 3
Dokumenttyp: Artikel
Förlag: PERGAMON-ELSEVIER SCIENCE LTD

Sammanfattning

In the equation for thermal energy output from a flat-plate solar collector (written as a function of the collector mean heat carrier temperature), both the gain and the loss terms are multiplied by the collector efficiency factor, F'. For a concentrating collector with an uneven (non-uniform) irradiation on the absorber, the efficiency factor for the gain term, here called the optical efficiency factor, F-c', is different from F' and is a function of the irradiation distribution on the absorber. If the heat loss coefficient is assumed to be constant across the fin, the optical efficiency factor for absorbed irradiation at a certain distance from the edge of the absorber is independent of absorbed irradiation at other locations and can therefore be expressed F-c'(x), where x is the distance from the edge of the absorber. Close to the edge, F-c'(x) < F' and close to the pipe, F-c'(x) > F'. In this paper formulas are derived for calculating F-c'(x) for a fin absorber with constant fin thickness. By weighting F-c'(x) with the absorbed irradiance, S-c(x), and integrating across the absorber, an absorber average optical efficiency factor, F-c,F-a', is obtained. This value replaces F' in the gain term of the equation for thermal energy output. If, instead, the energy output equation is expressed as a function of the inlet temperature, F-c,F-a' can be used for calculating a corresponding heat removal factor for uneven irradiation, F-R,F-c. Formulas for calculating the temperature distribution across the absorber for the case of uneven irradiation are also derived. (C) 2004 Elsevier Ltd. All rights reserved.

Disputation

Nyckelord

  • Technology and Engineering
  • uneven irradiation
  • concentrating solar collector
  • efficiency factor
  • non-uniform irradiance

Övriga

Published
Yes
  • ISSN: 0038-092X

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