Optimizing photothermal conversion efficiency in a parabolic trough direct absorption solar collector through ferrofluid and magnetic field synergy

Improving surface absorption of solar radiation is a critical challenge due to the negative impact of endothermic coating and significant heat loss during energy transfer. In this study, magnetic nanofluids are proposed as the thermal medium in a parabolic trough direct absorption solar collector to overcome the limitations of surface absorption and improve solar energy utilization. Thermal and exergy analyses are performed for the parabolic trough direct absorption solar collector to evaluate the potential of magnetic nanofluids in photothermal conversion under various magnetic fields. The present work experimentally investigates the heat transfer and efficiency of ferrous-ferric oxide-water nanofluids. The nanofluids have nanoparticle concentrations ranging from 0.01 wt% to 0.40 wt% and flow rates from 50 L/h to 100 L/h. The results indicate that the optimal nanoparticle concentration of 0.20 wt% achieves maximum gains in heat transfer, thermal efficiency, and exergy efficiency compared to deionized water. Specifically, a 161.0 % increase in heat production, a 26.1 % increase in thermal efficiency, and a 2.4 % increase in exergy efficiency are observed. Furthermore, when exposed to S-S magnetic fields, a 226.0 % increase in heat production, a 40.2 % increase in thermal efficiency, and a 4.0 % increase in exergy efficiency are achieved for the magnetic nanofluid with a ferrous-ferric oxide nanoparticle concentration of 0.20 wt%, also compared to deionized water. The combined application of ferrofluid and magnetic fields shows promise as an effective means for utilizing solar energy efficiently. The results and generalized criteria are of great significance for designing and optimizing direct absorption solar collectors, which will indirectly contribute to reducing carbon dioxide emissions by promoting more efficient solar energy utilization.