Derivation of efficiency factors for uneven irradiation on a fin absorber
(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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https://lup.lub.lu.se/record/263029
- author
- Hellström, Bengt LU
- organization
- publishing date
- 2004
- 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
- 2016-04-01 16:00:46
- date last changed
- 2022-01-28 08:44:16
@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) < 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.}},
author = {{Hellström, Bengt}},
issn = {{0038-092X}},
keywords = {{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}},
doi = {{10.1016/j.solener.2004.06.002}},
volume = {{77}},
year = {{2004}},
}