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Derivation of efficiency factors for uneven irradiation on a fin absorber

Hellström, Bengt LU (2004) In Solar Energy 77(3). p.261-267
Abstract
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... (More)
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. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
uneven irradiation, concentrating solar collector, efficiency factor, non-uniform irradiance
in
Solar Energy
volume
77
issue
3
pages
261 - 267
publisher
Elsevier
external identifiers
  • wos:000224446000001
  • scopus:4344615840
ISSN
0038-092X
DOI
10.1016/j.solener.2004.06.002
language
English
LU publication?
yes
id
bd8d695b-5632-4f0f-9e7c-4f4555b0db66 (old id 263029)
date added to LUP
2007-10-29 16:19:46
date last changed
2017-01-01 06:53:17
@article{bd8d695b-5632-4f0f-9e7c-4f4555b0db66,
  abstract     = {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) &lt; F' and close to the pipe, F-c'(x) &gt; 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.},
  author       = {Hellström, Bengt},
  issn         = {0038-092X},
  keyword      = {uneven irradiation,concentrating solar collector,efficiency factor,non-uniform irradiance},
  language     = {eng},
  number       = {3},
  pages        = {261--267},
  publisher    = {Elsevier},
  series       = {Solar Energy},
  title        = {Derivation of efficiency factors for uneven irradiation on a fin absorber},
  url          = {http://dx.doi.org/10.1016/j.solener.2004.06.002},
  volume       = {77},
  year         = {2004},
}