Derivation of efficiency factors for uneven irradiation on a fin absorber
(2004) In Solar Energy 77(3). p.261267 Abstract
 In the equation for thermal energy output from a flatplate 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 (nonuniform) irradiation on the absorber, the efficiency factor for the gain term, here called the optical efficiency factor, Fc', 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 flatplate 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 (nonuniform) irradiation on the absorber, the efficiency factor for the gain term, here called the optical efficiency factor, Fc', 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 Fc'(x), where x is the distance from the edge of the absorber. Close to the edge, Fc'(x) < F' and close to the pipe, Fc'(x) > F'. In this paper formulas are derived for calculating Fc'(x) for a fin absorber with constant fin thickness. By weighting Fc'(x) with the absorbed irradiance, Sc(x), and integrating across the absorber, an absorber average optical efficiency factor, Fc,Fa', 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, Fc,Fa' can be used for calculating a corresponding heat removal factor for uneven irradiation, FR,Fc. 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)
Please use this url to cite or link to this publication:
http://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, nonuniform irradiance
 in
 Solar Energy
 volume
 77
 issue
 3
 pages
 261  267
 publisher
 Elsevier
 external identifiers

 wos:000224446000001
 scopus:4344615840
 ISSN
 0038092X
 DOI
 10.1016/j.solener.2004.06.002
 language
 English
 LU publication?
 yes
 id
 bd8d695b56324f0f9e7c4f4555b0db66 (old id 263029)
 date added to LUP
 20071029 16:19:46
 date last changed
 20181121 20:38:06
@article{bd8d695b56324f0f9e7c4f4555b0db66, abstract = {In the equation for thermal energy output from a flatplate 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 (nonuniform) irradiation on the absorber, the efficiency factor for the gain term, here called the optical efficiency factor, Fc', 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 Fc'(x), where x is the distance from the edge of the absorber. Close to the edge, Fc'(x) < F' and close to the pipe, Fc'(x) > F'. In this paper formulas are derived for calculating Fc'(x) for a fin absorber with constant fin thickness. By weighting Fc'(x) with the absorbed irradiance, Sc(x), and integrating across the absorber, an absorber average optical efficiency factor, Fc,Fa', 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, Fc,Fa' can be used for calculating a corresponding heat removal factor for uneven irradiation, FR,Fc. 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 = {0038092X}, keyword = {uneven irradiation,concentrating solar collector,efficiency factor,nonuniform irradiance}, language = {eng}, number = {3}, pages = {261267}, 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}, }