Optical and thermal testing of convection reduction mechanisms in a new 1.2X CPC solar collector

Maria Joao Carvalho; Manuel Collares-Pereira; Joao Correia de Oliveira; Joao Farinha Mendes; A. Haeberle; Volker Wittwer

doi:10.1117/12.185402

9 September 1994 Optical and thermal testing of convection reduction mechanisms in a new 1.2X CPC solar collector

Maria Joao Carvalho, Manuel Collares-Pereira, Joao Correia de Oliveira, Joao Farinha Mendes, A. Haeberle, Volker Wittwer

Author Affiliations +

Proceedings Volume 2255, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XIII; (1994) https://doi.org/10.1117/12.185402
Event: Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XIII, 1994, Freiburg, Germany

Abstract

A new non-evacuated solar collector of the CPC type, developed and manufactured in Portugal, is now commercially available. Its design features are unique and deserve a careful study, both of its optical and of its thermal characteristics. The optics is interesting given the unusual shape and the opportunity to test different convection suppression schemes and determine their impacts on the collector's optical performance. As for the collector's thermal behavior it is very interesting to test how simple (and potential marketable) different convection suppression ideas can improve an already very good collector from the heat loss point of view (FU_L equals 4.0 W/( degree(s)C.m²)). In the course of the paper a brief description of the collector is given and testing results are presented for the testing carried out in the following situations: (1) (i) measurement of its optical and thermal performance (instantaneous efficiency curve) measured both in E.W. and N.S. collector orientation (the collector has a very wide acceptance angle allowing it to work in N.S. orientation and, thus, function in a thermosyphon mode like any regular flat plate collector, (ii) measurement of its angular acceptance function; (2) measurement of the instantaneous efficiency curve after the introduction of (i) a thin Teflon high transmissivity film below the glass cover, (ii) transparent insulation of the capillary type, inserted also under the glass cover, (iii) measurement of the acceptance angle function in this last situation. In this paper it is shown that the addition of the film reduces the heat loss coefficient by a factor of 1.3 W/( degree(s)C.m²) and the transparent insulation leads only to an improvement of 1.0 W/( degree(s)C.m²) in that same coefficient.

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Maria Joao Carvalho, Manuel Collares-Pereira, Joao Correia de Oliveira, Joao Farinha Mendes, A. Haeberle, and Volker Wittwer "Optical and thermal testing of convection reduction mechanisms in a new 1.2X CPC solar collector", Proc. SPIE 2255, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XIII, (9 September 1994); https://doi.org/10.1117/12.185402

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