Investigation of thermal conductivity and tribological properties of nanofluids.

摘要

Nanofluids are engineered by dispersing and stably suspending nanoparticles with typical length on the order of 1–50 nm in traditional fluids. In the past decade, scientists and engineers have made great progresses in finding that a very small amount (< 1 vol %) of dispersed nanoparticles can provide dramatic improvement in the thermal properties of the base fluids. Therefore, numerous mechanisms and models have been proposed to account for the thermal enhancement of nanofluids. The molecular dynamics (MD) simulation has become an important tool in the study of dynamic properties of liquids, molecular solutions, and macromolecules. Therefore, MD simulation is a very helpful tool to model the enhanced thermal conduction and predict thermal conductivities of nanofluids.;In recent years, investigations on the tribological properties of nanofluids have also been carried out. Some papers have reported that nanofluids are effective in reducing wear and friction. The mechanisms of friction reduction and anti-wear of nanoparticles in lubricants have been reported as colloidal effect, rolling effect, protective film, and third body.;The objective of this research is to study the thermal conductivity and tribological properties of nanofluids. The thermal conductivity of nanofluids was investigated theoretically through MD simulation. Nanodiamond was selected as the nanoparticle and octane as the base oil. The Large-scale Atomic-Molecular Massively Parallel Simulator (LAMMPS) was used. The effects of the particle size, shape and concentration on the thermal conductivity of nanofluids was investigated. The thermal conductivity of oil based nanofluids with nanodiamond particles was also measured experimentally using transient hot-wire method.;The tribological properties of nanofluids were studied through experimental investigation using commercially available nanopowders and nanofluids. Both water based and oil based nanofluids were investigated. A Universal Micro-Tribometer with a ball-on-disk configuration was used to evaluate friction properties between the moving mechanical components with the presence of nanofluids. Wear track and wear volume were measured by WYKO 3D surface profiler, and material deposition on the sliding interface was analyzed with an X- ray photoelectron spectroscopy. The effects of nanoparticle concentration, particle type, surface roughness and operation conditions on the friction and wear performance of nanofluids were considered.