Thermal conductivity and viscosity measurements of water-based silica nanofluids

Nanofluids are a new class of fluids that could significantly improve the thermal properties of fluids used as thermal vectors. They are obtained by dispersing in common fluids (water, glycol, oil) solid nanoparticles (diameter <100 nm) of different materials (metal oxides, metals, carbon nanotubes). Also at relatively low nanoparticle concentrations, it is possible to get an unproportional increase in thermal conductivity and heat transfer coefficient, with a correspondent increase of the energy efficiency of plants or components using such fluids. In general, the higher the concentration, the higher the heat transfer enhancement. Other important parameters influencing the enhancement are material, dimension and shape of the nanoparticles, Zeta potential, pH, type and concentration of dispersants. However, nanofluids can be actually applied in technological systems only if the addition of nanoparticles does not determine a significant viscosity enhancement, because the increase of energy required to pump the nanofluid could nullify the advantages obtained in terms of thermal properties. In the literature, several papers present measurements of thermal properties and/or viscosity for water based nanofluids and various kinds of added nanoparticles showing different behaviors.