Comparative investigations on thermal performance assessment of a linear parabolic trough solar collector using various nanofluids and incident angles

Among the various solar collectors, the Parabolic Trough Solar Collector (PTSC) has been reported to be the most widely used in applications such as steam production and process heat distribution. In this study, an experimental investigation was conducted to evaluate the thermal performance of the PTSC when different nanofluids were used as the working fluid. Two nanofluids, i.e., CuO and Al2O3, dispersed in deionized water (base fluid) at three different mass concentrations (0.05 %, 0.075 %, and 0.1 %), were used as the heat transfer fluid (HTF). The experiments were performed at different incident angles and volume flow rates (70 L/h and 140 L/h). The inclusion of nanoparticles improved the thermophysical characteristics of the base fluid, which enhanced heat transfer between the working fluid and the receiver tube. For all nanofluids tested under various ambient temperatures and incidence angles, there was an increase in the PTSC's thermal efficiency compared to the base fluid. It was observed that the incident angle significantly influenced the efficiency of the nanofluids, and, consequently, the PTSC's performance, with the smallest angle yielding the highest efficiency. For CuO nanofluid concentrations (0.05 %, 0.075 %, and 0.1 %), efficiency increases of 28.02 %, 34.47 %, and 41.26 % were observed at a mass flow rate of 70 L/h, respectively. Similarly, for Al2O3 nanofluid concentrations (0.05 %, 0.075 %, and 0.1 %), efficiency increases of 14.6 %, 18.17 %, and 24.79 % were observed at the same mass flow rate. It was concluded that at lower inclination angles, the thermal efficiency of the PTSC was higher compared to higher inclination angles for all nanofluid concentrations.