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Corresponding Author

Gad, Helmy

Subject Area

Mechanical Power Engineering

Article Type

Original Study

Abstract

This paper presents a new approach to the thermal analysis of a solar concentrator. The Signal Flow Graph technique is applied to solve the heal Transfer problem in a flat receiver subjected to nonuniform flux distribution. Signal Flow Graph allows in a more easy graphical form to express the essential properties of the analyzed system, and directly obtain any parameter from the graph structural properties. With this method, there is no need of assuming uniform flux distribution over the whole receiver surface as in Hottel-Whillier-Woertz-Bliss approach, A Computer program has been established to obtain the thermal performance under different design and operating conditions using both approaches. In order to verify the theoretical results, an experimental concentrator was built with, one glass cover, flat receiver of 25 cm width and 94 cm length, The receiver is insulated with form plates of 3 cm thickness and fitted with two headers to supply the fresh water uniformly in the length direction. The reflecting surface is formed of unequal mirror segments which are arranged to concentrate most of the falling solar radiation on the upper third of the receiver surface. The set-up is suitably instrumented to measure the temperature at different points and the water mass flow rate through the receiver. The total and beam solar radiation intensities as well as the ambient temperature are also measured during the experimental work. Comparison between the predicted and measured results have shown that the thermal performance as calculated by the Signal Flow Graph is more fitted with the experimental results than that obtained by the HWWB approach. Therefore, the Signal Flow Graph approach is seen to be an easy and precise technique for the thermal analysis of concentrating collectors with nonuniform flux distribution on the receiver surface.

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