Performance improvement of a nanofluid solar collector based on direct absorption collection (DAC) concepts

Nanofluids are engineered colloidal suspensions of nanoparticles in base fluids, which have good properties of radiation absorption and heat transfer and are a kind of potential working fluids for solar collector based on direct absorption collection (DAC) concepts. A simulation model of nanofluid solar collector was built based on DAC concepts by solving the radiative transfer equations of particulate media and combining conduction and convection heat transfer equations. The system efficiency and temperature distributions are analyzed by considering the absorption and scattering of nanoparticles and the absorption of the matrix. The simulation results were in accordance with the experiments'. The nanofluids improved the outlet temperature and the efficiency by 30-100 K and by 2-25% than the base fluid. The photothermal efficiency of a 0.01% graphite nanofluid is 122.7% of that of a coating absorbing collector. The study indicated that nanofluids, even of low-content, have good absorption of solar radiation, and can improve the outlet temperatures and system efficiencies.