Improving the overall thermal performance of parabolic trough solar collectors using porous media

Ihe of use porous irsert constituted by a metal matrix of copper Raschig Rings is proposed here for parabolic trough solar collectors. The CFD analysis, based on a well-established numerical model, allows computing a significant increase in the thermal performance of the lube considered in the analysis, when equipped with the porous insert, with respect to a smooth pipe. The useful power grows up to -96 % of the absorbed incident power. A reduction of a factor of 5 in the radiative and convcctivc losses is computed, due to a large drop in the pipe surface temperature. The length of the porous insert, however, should be carefully evaluated in view of the significant additional pressure drop caused by the insert.