Experimental analysis of copper foam thicknesses and non-uniform configurations on the performance of direct absorption parabolic trough collectors

Abstract

Enhancing the thermal efficiency of direct absorption parabolic trough collectors is a fundamental challenge in advancing solar energy technologies, as improved heat absorption directly impacts overall system performance. This study experimentally investigates the influence of copper porous foams on the thermal performance of a direct absorption parabolic trough collector, aiming to optimize efficiency by analyzing various porous foam configurations under varying inlet temperatures (20 °C, 30 °C, and 40 °C) and flow rates (20–120 Lph). Four foam thicknesses, representing 25 %, 50 %, 75 %, and 100 % of the absorber tube’s inner radius, were tested in full and semi-porous arrangements. Additionally, two innovative gradient foams with radially variable pore densities—one increasing and one decreasing—were developed and analyzed. The results indicated that increasing foam thickness enhanced thermal efficiency, with maximum improvements of 111.6 %, 125.5 %, 133.9 %, and 143.9 % for the 25 %, 50 %, 75 %, and 100 % configurations, respectively. The full-porous 100 % foam achieved the highest thermal efficiency of 51.3 % (at 20 °C, 120 Lph) and a maximum temperature difference of 15.3 °C (at 20 Lph), albeit with the highest friction factor. The semi-porous arrangement yielded maximum efficiencies of 37.6 % and 44.8 % for 25 % and 100 % foams, respectively. The performance evaluation criteria for the 25 % copper foam in both full and semi-porous arrangements exceeded one, reaching a peak of 1.42, indicating it as the optimal configuration. Notably, the gradient copper foam with radially increasing pore density achieved a thermal efficiency of 50.3 %, comparable to the full-porous 100 % foam, but with reduced pressure drop, resulting in superior performance evaluation criteria.