Solar Energy Capture: Methods of Optimizing Nanofluid-Based Volumetric Solar Flow Receivers

Appropriately selected and prepared nanofluids have promised improved volumetric absorption for solar energy harvesting. This study explored methods of optimizing a graphite-Therminol VP-1 nanofluid volumetric solar flow receiver. Previous studies provided a means of selecting the optimum physical parameters of a rectangular flow receiver via a 2D analytical model. This model has been extended to include a specular reflective base, which demonstrated improvements in the overall efficiency. The refractive index of the absorbing medium was included, causing a spectral shift of incoming radiation. Smaller nanoparticle volume fractions were therefore required to achieve the optimum efficiency, which was also determined using the extended analytical model. A more realistic numerical model, prepared using Ansys Fluent, indicated that receivers with partially diffuse reflecting bases exhibited higher temperatures near the base, thereby minimizing surface losses and increasing average temperatures. The magnitude of these increases, however, may not warrant the use of these types of reflectors.