Radiation and nanoparticle interaction for enhanced light absorption and heat conversion

The photo-thermal conversion performance (PTCP) of water-based nanofluids in a volumetrically heated solar collector (VHSC) is evaluated. The influences of nanoparticle volume concentration (NVC), particle size, Reynolds number, operating temperature, and collector geometry on the PTCP are numerically investigated. The utilization of nanoparticles and improving their concentration is found to enhance the photo-thermal conversion efficiency (PTCE) of the collector by augmenting the energy from the sun of the working fluid due to the radiation-nanoparticle interactions. The PTCE enhancement of Graphite, TiO2 and Ag nanoparticles dispersed in water is respectively 1.37, 1.33 and 1.29 times better, compared to that of water. This is further augmented by adding MgO nanoparticles to TiO2, Graphite and Ag particles, resulting in 1.69, 1.67 and 1.59x improved efficiency. Enhancing the flow rate of the fluids also contributes to the PTCE by reducing the losses of thermal from the collector to the ambient. Besides, the enhanced nanoparticle size increases the overall PTCP as it enables the nanofluid to absorb more solar energy. Enhancing the collector length accelerates the thermal loss to the ambient, as a result the system performance diminishes. It is also regarded that the heat absorption of the nanofluid declines with improving inlet temperature of the working fluid.