Transient Analysis of a Flat-Plate Direct Absorption Solar Collector with Nanofluids

The thermal performance of a direct absorption solar collector (DASC) can be improved by enhancing the absorbing plate or the effectiveness of the heat transfer fluid. This can be achieved by using a nanofluid instead of pure water, as it possesses better optical properties. This paper conducts numerical simulations on a two-dimensional transient forced convection inside a DASC with a horizontal channel to predict its transient thermal behavior in a specific geographical location under varying hourly solar radiation. The working fluid used is a nanofluid comprised of water and carbon nanohorn nanoparticles, with concentrations ranging from 0 (pure water) to 0.05 g/L. Additionally, the inlet mass flow rate has five varying values from 0.001 to 0.2 kg/s. Results detailing temperature and system efficiency are presented, with their evolution throughout the day also reported. The analysis indicates that the system's performance improves with increasing concentration for each inlet mass flow rate value. Conversely, keeping the concentration constant, the temperature rises as the inlet mass flow rate decreases.