Numerical Simulations of an Al2O3-Water Nanofluid-Based Linear Fresnel Solar Collector

This study aims to numerically investigate the performance of Al2O3-water nanofluid as a heat transfer fluid (HTF) in a linear Fresnel solar receiver. Although a reasonable number of studies have investigated the thermal behaviors of different nanofluids as HTF in solar collectors, the focus has so far been on the parabolic trough collectors, with little or no research efforts available for the linear Fresnel collectors. ANSYS-fluent software was utilized for the simulation in this study, which converted the governing equations to algebraic forms based on the control-volume approach. The Nusselt number and wall temperature were used to characterize the thermal performance of the nanofluid, while the friction factor and eddy viscosity were considered to determine the flow features. The correlation equation proposed by Gnielinski was used to determine the Nusselt number, while the flow features were computed using the Darcy-Weisbach equation. Additionally, the thermal performance of the nanofluid was compared directly with that of pure water. Results showed that the nanofluid improved the thermal performance by about 6-19 % across the solar receiver length. Also, the Nusselt number increases non-uniformly across the length, with a significant rise towards the trailing edge of the nanofluid flow. Conversely, the pressure drop also increases with an increase in the solar receiver length, albeit uniformly. Designers should always factor into the design process to determine the optimum solar collector length when a nanofluid is considered as the HTF; to maximize heat transfer and minimize pressure drop and its attendant economic consequences.