Enhanced thermophysical properties of NEILs as heat transfer fluids for solar thermal applications

Thermophysical properties of base ionic liquids (ILs) and nanoparticle enhanced ionic liquids (NEILs) were measured experimentally. NEILs are formed by dispersing different wt% (0.5, 1.0, and 2.5) of Al2O3 nanoparticles in four base ILs. NEILs show enhanced thermal conductivity, viscosity, and heat capacity compared to the base ILs. NEILs show shear thinning behavior at all the measured temperatures and the enhancement of viscosity was predicted by the aggregation model with high aggregation factor. Maximum thermal conductivity enhancement was observed by ∼11% for 2.5 wt% NEILs. The experimental effective thermal conductivity could not predicted by the aggregation model with the same aggregation factor. However, the theoretical model considering interfacial layer of the particle/liquid interface (with interfacial layer thickness 2 nm and interfacial layer thermal conductivity, klr=3kBL) could predict the effective thermal conductivity of NEILs. Heat capacity of NEILs shows much higher value compared to the base ILs and the theoretical model could not predict that enhancement. The strong interaction between the nanoparticles surface to ions of the ionic liquids was considered as the potential factor for those enhancements of thermophysical properties.