Abstract
Nanofluid is defined as a nanoparticle suspension in the base fluid. Tremendous enhancement of thermal conductivity of nanofluids has been observed in the experiment, which leads to the applications for energy saving. This paper aims to calculate the thermal conductivity of nanofluids, and to identify the physical mechanism of enhancement by Molecular Dynamics simulation. Position and velocity of each atom, and the interaction between atoms are obtained by Molecular Dynamic simulation, and thus the physical coefficients, such as melting point, boiling point, viscosity, thermal conductivity of a system of substance can be modeled by these quantities. Among these physical properties, thermal conductivity is the most difficult quantity to calculate by Molecular Dynamics simulation. Two approaches of calculating thermal conductivity by molecular dynamic method, non-equilibrium method (NEMD) and Green-Kubo method, are explored and compared after system reaching equilibrium state. The results show that different values are obtained if the number of atoms in the nanoparticle is larger than 10 atoms. The physics will be identified and discussed in detail to reach reasonable conclusion. Furthermore, the low volume fraction nanofluids are composed of a large number of atoms, which implies the impossible computer resource required, therefore, a simplified shell model is derived to estimate the thermal conductivity of nanofluids, so that the comparisons with the experimental results can be conducted.