PREDICTED HEAT-TRANSFER PERFORMANCE OF AN EVACUATED GLASS-JACKETED CPC RECEIVER: COUNTERCURRENT FLOW DESIGN

ABSTRACT:
The heat-transfer performance of an evacuated glass-jacketed CPC-receiver facility, free on one end and fixed onto the glass jacket at the other, has been carried out using heat-transfer relationships and the best information available in the literature. Specifically, the collector

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examined was a 3x-CPC facility, 8 ft (2.44 m) long, with an entrance aperture 4.5 in. (11.43 cm) wide covered with a single glass cover, and provided with an aluminum reflecting surface (p = 0.88). To maximize heat retention, a selectively treated receiver surface, E = 0.11, was used. The optical efficiency of this CPC collector facility was calculated to be n 0 = 0.536. The heat reaching the surface of this receiver was transferred to liquid Dowtherm A flowing through this facility. The configuration within this receiver was of a reverse concentric flow design, with liquid dowtherm A entering the annular space and leaving through the tube located concentrically to it. This countercurrent arrangement necessitated the development of specific mathematical expressions for the temperature of the fluid within the annular space and through the inside of the concentric tube. A number of performance curves are presented that relate the overall efficiency of the collector with the temperature of the fluid entering and leaving this concentric receiver facility, using an incident insolation to the CPC collector of 200 Btu/hr ft 2 (630 watts/m2 ) and an ambient air temperature of 100°F (37.8°C). In addition, related performance curves are presented for the average temperature of the glass jacket and receiver surface, and the highest temperature of the fluid prevailing at the entrance of the inner tube.

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