Experimental study on the thermal performance and heat transfer characteristics of solar parabolic trough collector using Al₂O₃ nanofluids

The present work investigated thermal performance and heat transfer characteristics of a solar parabolic trough collector using Al₂O₃/DI-H₂O nanofluids. Nanofluids of varying concentrations (0.05% ϕ ≤ 0.5%) with mass flows (0.0083–0.05 kg/s) were considered for turbulent regime (2401 ≤ Re ≤ 7202) analysis. Experiments were carried out as per ASHRAE 93(2010) standards. By thermal performance analysis using Al₂O₃ nanofluid, it was understood that the collector efficiency improved up to 56% at a maximum volume concentration of ϕ = 0.5% and flow rate of 0.05 kg/s. The heat transfer study comparing Al₂O₃ nanofluid with pure water showed appreciable reduction in temperature gradient and surface temperature of the absorber. The heat transfer characteristics such as Nusselt number and friction factor relating to Reynolds number fits the experimental and predicted data and found within the limits of ±5.35% and ±9.61% for Nusselt number and friction factor respectively. Moreover, a similar empirical correlation was developed for collector efficiency, which was identified to be within the limit of ±1.02%.