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Computational and Experimental Investigation of Internal Natural Convection in a Solar Micro-Concentrating Collector
Tanzeen Sultana, Graham Morrison, Matthew L Hoffman and Gary Rosengarten

In solar thermal systems, heat loss can significantly reduce the efficiency and consequently the cost effectiveness. It is therefore vital to fully understand the nature of the heat loss mechanisms. This paper describes the thermal performance of a new low-cost solar thermal micro-concentrating collector (MCT), which uses linear Fresnel reflectors, and is designed to operate at temperatures up to 200°C. The modules of this collector system are approximately 3.2 meters long by 1.2 meter wide and 0.3 meters high. The numerical and experimental study of combined laminar natural convection and surface radiation heat transfer in the cavity receiver of the MCT is presented. This paper describes the numerical and experimental investigation of the collector heat losses at inclinations varying from 0 to 40°, and absorber temperatures ranging from 70°C to 200°C. In addition to measurements of overall heat loss, particle imaging velocimetry (PIV) was used to visualize the flow field within the enclosure. Excellent qualitative and quantitative agreement of the flow field is achieved between the experiment and that predicted by the computational model. A three-dimensional simulation model for combined natural convection and surface radiation is also developed.

Keywords: Solar thermal energy, solar concentrator, computational fluid dynamics (CFD), heat loss, particle image velocimetry (PIV), natural convection.

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