Transport properties of nanofluids. A critical review

Nanofluids are suspensions of nano-size particles (typically 2 to 100 nm) in liquids. Several research projects in the late 1990s and the first decade of the 21st century indicated that the addition of very small amounts of nanoparticles in common cooling fluids increases significantly the effective thermal conductivity of the suspensions and their convective heat and mass transfer coefficients. While typical experimentally determined conductivity enhancements were in the range of 10–50%, some early experiments exhibited enhancements higher than 100%. Experiments on the mass transfer coefficients and the viscosity of these solid–liquid suspensions reported more dramatic results with maximum mass transfer enhancements in the range of two to six times that of the base fluid. Such experimental observations indicate that appropriately designed engineering systems operating with suitable nanofluids will have heat and mass transfer characteristics that are superior to currently used fluids.