LAUSR

Abstract In this study, the influence of toroidal rings in an absorber tube of a solar parabolic trough collector (SPTC) operating with air, carbon dioxide (CO2) and helium (He) is investigated with detailed energy and exergy analysis. Nine different cases of the modified absorber have been investigated and compared with the smooth absorber tube (SAT). Under varying fluid flow rate and inlet temperatures, the heat transfer tendency in the absorber tube has been numerically studied and validated. The modified absorber having a diameter ratio (H) of 0.88 and 0.90 are the thermally and exergetically efficient optimal cases, respectively, with ˋH′ being the ratio of inner to outer diameter of the toroidal ring. The bottom periphery temperature difference for the case H = 0.88 operating with He is found to be 8 K, and it is the lowest among all the examined cases. A maximum exergy efficiency of about 41.23% is achieved for the case H = 0.90 with He. For thermal efficiency, air has higher magnitude with tremendous increase in pressure drop followed by CO2 and He. Hence, the outcomes reveal that He is the appropriate working fluid exhibiting higher exergetic performance and lower pressure drop followed by CO2 and air.