Enhancing solar collector performance: An experimental study on zigzag rectangular angled strips and nanofluid integration

Solar thermal collectors are increasingly popular for harnessing renewable energy to meet global energy demands sustainably. These systems convert solar radiation into thermal energy for residential, commercial, and industrial use. Enhancing their efficiency, nanofluids-base fluids with suspended nanoparticles have been widely studied. This experimental research explores a flat-plate solar collector integrating zigzag rectangular angled strips within the absorber tube and using nanofluids such as MgO/DIW, ZnO/DIW, and Al2O3/DIW at 1.0 vol.% concentration. The study examines the thermal performance at 45? angled strips with pitch ratios (Y) of 2.0, 3.0, and 4.0 under identical conditions. Results show that for a pitch ratio of 2.0, MgO/DIW, ZnO/DIW, and Al2O3/DIW enhance heat transfer by 30%, 28%, and 22%, respectively, at higher Reynolds numbers compared to DIW. The Nusselt number increases by 45%, 42%, and 40%, with MgO/DIW consistently delivering the highest heat transfer enhancement. Thermal efficiency reaches approximately 85% for MgO/DIW nanofluids, outperforming DIW at lower pitch ratios. However, the friction factor rises by 15% for ZnO/DIW at lower Reynolds numbers, and pumping power increases by 10% for ZnO/DIW in zigzag strip tubes compared to plain tubes. These findings confirm that combining high thermal conductivity nanofluids and optimized zigzag strip designs significantly boosts the thermal efficiency of solar collectors. This research highlights the potential of nanofluid integration and geometric modifications for advancing solar energy technologies.