Enrichment and thermal performance of solar based heat exchanger featured with alumina/graphene hybrid nanofluid

Abstract Solar thermal energy is well recognized for enhancing the efficiency of solar heat exchangers, benefiting from its effective heat transfer from solar collectors to the working fluid. Advantages include lower operating costs, sustainability, and environmental benefits. However, conventional water-based solar systems face limitations such as lower thermal conductivity, reduced boiling temperature, and limited absorption behaviour, which collectively diminish thermal efficiency. This study examines solar thermal heat exchangers operating with a hybrid nanofluid composed of alumina and graphene nanoparticles in a 50:50 ratio. The hybrid nanofluid is tested at different volume concentrations of 0.5%, 1%, 1.5%, and 2% while maintaining a constant flow rate with 13LPM. The nanofluid is prepared using an ultrasonication process, and its microstructural characteristics are confirmed through transmission electron microscopy analysis. The performance impact of the hybrid nanofluid concentrations on solar-based heat exchangers is investigated. The system operates most effectively at a 1.5% concentration of hybrid nanofluid, showing significant improvements in heat transfer rates, convective heat transfer coefficients, outlet temperatures, and overall thermal and exergy efficiencies. These parameters demonstrate improvements of 10.6%, 20.3%, 13.7%, 13.2%, and 26% compared to the thermal performance of standard solar heat exchangers operating with water. Additionally, there is a minimal increase in pressure drop, measuring around 15.1% at the 1.5% volume concentration. This study highlights the potential of alumina/graphene hybrid nanofluids to enhance thermal performance in solar collectors while maintaining a low impact on pressure loss.