Enrichment of Solar Heat Exchanger Thermal Performance by the Integration of Beeswax and Hybrid Nanofluid (ZnO/MgO)

Solar heat exchangers have the potential for sustainable energy utilization and unique properties like being cost-effective, transferring heat more efficiently, and being eco-friendly. However, the thermal performance of heat exchangers is reduced due to poor weather conditions, unrated solar radiation, and a lack of latent heat energy storage. This study aims to resolve disputes and enhance the solar thermal performance of flat plate solar collectors that utilize beeswax phase change material (PCM) and a hybrid nanofluid composed of 50% zinc oxide (ZnO) and 50% magnesium oxide (MgO) at concentrations of 1–3 vol%, operated at a flowrate of 2 l/min. The different volume concentrations include hybrid nanofluid (ZnO/MgO) at 1 vol%, PCM mixed with hybrid nanofluid (ZnO/MgO) at 2 vol%, and PCM combined with hybrid nanofluid (ZnO/MgO) at 3 vol%. The use of the hybrid nanofluid results in an improved heat transfer rate, reduced heat loss, greater latent heat storage, and enhanced thermal and exergy efficiency compared to water. Specifically, the ZnO/MgO at a concentration of 3 vol% exhibits the highest thermal conductivity, reaching approximately 0.93 W/m/K. It also achieves an outlet temperature of 91.5 °C, a heat transfer rate of around 398.4 W, and a latent heat storage capacity of about 389.1 kJ/kg. Additionally, the typical thermal efficiency is approximately 68.6%, while the average exergy efficiency is about 30.1%.