On the effect of different placement schemes of metal foam as volumetric absorber on the thermal performance of a direct absorption parabolic trough solar collector

Abstract

The main message of this paper is to answer the question of how the thermal efficiency of a direct absorption solar collector is affected by the placement scheme of porous foam in its absorber tube. Hence, ten different layouts of open cell copper porous foam are examined. The thermal efficiency of a constructed direct absorption parabolic trough solar collector is obtained in three different inlet temperatures (20, 30, and 40 °C) and five flow rates (40, 60, 80, 100, and 120 Lph) for various layouts. The results revealed that the placement of porous foam in the lower half of the absorber tube than the upper half leads to a higher thermal efficiency. The highest obtained thermal efficiencies for cases where the entire of absorber tube, center of it, and perimeter of it were filled with porous foam were 50.8%, 46.1%, and 44.7%, respectively. The placement of porous foam in the center of the absorber tube leads to higher pressure drop and thermal efficiency than peripheral placement. Considering the performance index, the peripheral placement of porous foam in the absorber tube is preferred. Moreover, porous foam with higher pore density (PPI) can lead to a higher thermal efficiency.