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Comparison of modelled heat transfer and fluid dynamics of a flat plate solar air heating collector towards experimental data

: Reichl, C.; Kramer, K.; Thoma, C.; Benovsky, P.; Lemée, T.


Solar energy 120 (2015), S.450-463
ISSN: 0038-092X
ISSN: 0375-9865
Fraunhofer ISE ()
Solarthermie und Optik; Servicebereiche; TestLab Solar Thermal Systems; air-heating collectors; thermal; test; modelling

Research concerning the field of Liquid Heating Collectors (SLHCs) cannot be directly transferred to the large area of applications for Solar Air Heating Collectors (SAHC). Larger cross sections for transporting the air are necessary. This results in rather complicated fluid distributions within the products. In this paper we combine simulation and experimental techniques providing a high level of detail. Highly resolved three dimensional fluid dynamic simulations contain all the relevant heat transfer mechanisms in a plate SAHC: Heat conduction, convection patterns and radiation are modelled in the two air gaps. In all solid materials of the collector only heat conduction has to be accounted for. For the exchange of heat between the two air zones the heat transfer through the absorber is modelled. Nevertheless careful simplification is needed to be able to concentrate on the important details. Furthermore we shed light on numerical instabilities observed in the air gap between absorber and glass in the simulated example. A consistent numerical description is given, concluding, that Computational Fluid Dynamics (CFD) is an appropriate tool for design and optimisation of SAHC concepts. The effects of collector tilting, insulation level and heat transfer surface increase have been assessed as a prove of applicability. The performance of these models will finally be compared to the experimental data obtained using a high-precision SAHC testing facility. For the experimental data base refined local measurement techniques, which meet highest accuracy requirements, are developed and employed.