Thermophysical properties of nanofluids

This paper discusses the current state of knowledge of the thermophysical properties of nanofluids. The viscosity, thermal conductivity and heat transfer of nanofluids are considered. Experimental and molecular dynamics data are presented. It is shown that viscosity and thermal conductivity of nanofluids generally cannot be described by classical theories. The transport coefficients of nanofluids depend not only on the volume concentration of the particles but also on their size and material. The viscosity increases with decreasing the particle size while the thermal conductivity increases with increasing the particle size. The reasons for this behavior are discussed. The heat transfer coefficient is determined by the nanofluid flow mode (laminar or turbulent). The use of the nanofluids as a coolant significantly affects the magnitude of the heat transfer coefficient. In laminar flow the heat transfer coefficient of nanofluids in all cases is much more than that of base fluids. It is shown that a 2%-nanofluid intensifies the heat exchange more than twice compared to water. The effect of using nanofluids in turbulent mode depends not only on the thermal conductivity of the nanofluid, but also on its viscosity.