REFLECTING RADIATION TRAP FOR PRODUCING HIGHER TEMPERATURES IN FLAT-PLATE SOLAR COLLECTORS.

This paper presents analyses of a proposed mechanical means for decreasing the effective emissivity of a flat-plate solar collector. The proposed reflecting radiation trap involves the incorporation of rectangular channels with reflecting serrated walls on the sun-side of the flat-plate collector. The rectangular channels effectively reduce the emissivity of the surface by reflecting some of the emitted radiation back onto the emitting surface (the absorber plate of the collector). The 'real' or engineering-model traps were analyzed as functions of trap configuration, wall reflectivity and emissivity, insolation, conduction-convection losses, and equilibrium temperatures. It was found that the trapping means do increase the effective absorptivity of the collector while decreasing the effective emissivity, and in effect increases the alpha / epsilon ratio for the surface. The trap is seen to be sensitive to insolation incidence angle (acceptance angle) in the plane perpendicular to the walls and base of the trap. The results also show that although the trap does increase the operating temperatures of flat-plate solar collectors for a given set of insolation and environmental conditions, the optimum use of the trapping concept probably will be in conjunction with sun-tracking collectors.