Experimental performance evaluation of an auto-tracking parabolic trough solar collector with recirculation of nanofluids

This study explores thermal performance enhancement in a parabolic trough solar collector (PTSC) equipped with an auto-tracking system using zinc oxide (ZnO) nanofluids. The main aim is to assess the impact of varying nanofluid concentrations and flow rates on the collector’s efficiency under climatic conditions of Lahore during the summer. Nanofluids were prepared by dispersing ZnO nanoparticles in distilled water at concentrations of 0.01 mass%, 0.015 mass%, and 0.02 mass%, while flow rates were varied by 0.01 kg s⁻¹, 0.015 kg s⁻¹, and 0.02 kg s⁻¹. A comparative analysis was performed between pure water and ZnO nanofluids, with and without recirculation. The results showed a considerable improvement in the PTSC’s thermal performance when using nanofluids and auto-tracking. Specifically, the maximum temperature achieved with water was 74 ℃, while for the nanofluid, it reached 81 ℃. At a flow rate of 0.02 kg s⁻¹, the system achieved thermal efficiency of 42.06% with water, which increased to 54.53% using a nanofluid at a flow rate of 0.015 kg s⁻¹ during peak solar radiation. The findings highlight the potential of ZnO nanofluids in enhancing the efficiency and heat gain of solar thermal systems, particularly under dynamic tracking conditions, showcasing the uniqueness and originality of this work.