Hybrid Nanofluids-Based Direct Absorption Solar Collector: An Experimental Approach

In the last years, studies have demonstrated the potential of hybrid nanofluids to enhance the performance of direct absorption solar collectors. These working fluids containing noble metals (gold, silver) are known for their local surface plasmon resonance which is the main cause for the increased absorption within the solar spectrum. In the current paper, new direct absorption solar collectors prototypes using water-ethylene glycol solution and 0.1 wt.% silver nanoparticles + reduced graphene oxide dispersed in water-ethylene glycol mixture were designed, built, and tested under outdoor conditions, at two flow rates (1.0 and 1.5 l·min⁻¹) and two inlet temperatures (20 \(^\circ{\rm C}\) and 30 \(^\circ{\rm C}\)), over several days in September 2023, at Brasov, Romania. The results suggested that by using silver nanoparticles + reduced graphene oxide nanofluid, the efficiency is improved related to water-ethylene glycol solution. The maximum relative enhancement in efficiency was 16.72% related to the base fluid. Also, at 1.0 l·min⁻¹, the instantaneous and accumulative energies delivered were about 13.51% and 42.91%, respectively, higher than the water-ethylene glycol solution. Finally, the current results were compared to other research carried out on full-scale direct absorption solar collectors tested in outdoor conditions.