Numerical simulations of a Cu–water nanofluid-based parabolic-trough solar collector

In this study, the thermal and flow characteristics of a parabolic-trough solar collector have been numerically investigated. The turbulent flow inside the receiver tube was modeled via the finite volume method, while a non-uniform concentrated heat flux was imposed on the absorber tube. A Cu–water nanofluid was specified as the heat transfer fluid. The results showed that increasing the Cu nanoparticle concentration led to an increase in the Nusselt number (Nu). Furthermore, the effect of Cu nanoparticle addition on the heat transfer enhancement became more significant as the Reynolds number decreased. This was because nanoparticle addition mainly improved the heat transfer via conduction. As the Reynolds number increased, the role of forced convection overcame that of conduction. Furthermore, it was shown that although Cu nanoparticle addition increased the thermal efficiency, it also increased the pressure drop slightly. The effect of direct normal irradiance changes on the performance of the solar collector was assessed. At Reynolds numbers of 10⁴, 10⁵ and 10⁶, as direct normal irradiance increased from 900 to 1100 W m⁻², Nu increased by up to 8.6%, 9.78% and 11.43%, respectively, leading to increases in thermal efficiency of 3.87%, 3.82% and 2.04%. This study provides new insight into the effect of Cu nanoparticle addition on the thermal and flow characteristics of parabolic-trough solar collectors.