Hybrid B4C/TiCN aqueous nanofluids for solar absorber applications

Nanofluid-based direct absorption solar collectors (NDASCs), where the transfer fluid also shows the solar absorption functionality, could offer advantages with respect to existing conventional surface-absorber thermal solar collectors, due to volumetric radiation absorption and reduced thermal resistance at the absorber-fluid interface. In the framework of investigation of novel nanofluids with favourable properties for NDASC applications, the present work is aimed to assess the stability (by dynamic light scattering), structural (by transmission electron microscopy and EDS) and optical properties (by optical transmittance measurements) of aqueous nanofluids containing boron carbide (B4C) and titanium carbonitride (TiCN), both as mono or hybrid nanodditives. The chosen B4C and TiCN materials are representative components of the family of so-called Ultra-High Temperature Ceramics (UHTCs), which are known for a number of appealing properties, among those high-temperature stability and promising bulk optical properties, while the optical properties at the nanoscale were unexplored to date. No formation of nanocomposites was evidenced, while optical properties of nanofluids resulted substantially changed with respect to the pure base fluid and promising for solar absorber applications. The dynamic viscosity was also evaluated, in order to check if the pumping power required for the flow of the new materials differs substantially, finding a Newtonian behaviour and a minimal viscosity increase.