FLOW AND HEAT TRANSFER SIMULATIONS FOR NANOFLUIDS WITH NANOPARTICLES OF VARIOUS DIAMETERS BY MOLECULAR DYNAMICS METHOD

摘要

This paper performs molecular dynamics simulations on flow and heat transfer process of nanofluids containing spherical nanoparticles with various diameters (2-6 nm). Instantaneous rotational velocity components of nanoparticles in a flow field with and without a temperature difference are outputted and compared. Number density method is used to examine the thickness of absorption layer. And by equally dividing the fluid into 60 fluid layers, temperature distributions of nanofluids and base fluid are examined. It was found that rotational speed of nanoparticle decreases with an increasing diameter. By applying temperature difference rotational speed of nanoparticles are generally increased. The rotational speeds of nanoparticles are generally about 1E9 rad/s. the rotation of nanoparticles is attributed to Brownian motion due to their nanoscale size. The diameter of nanoparticles has little effect on the thickness of the absorption layer, and the thickness of absorption layer is about 0.8 nm. By comparing temperature distributions of nanofluids and base fluid, it was found that the internal temperature difference in nanofluids is less than that of base fluid. And according the temperature gradient in nanofluids near the solid wall will be larger, which is better for heat transfer. This phenomenon is attributed to the fast-rotating nanoparticles accompanied by the absorption layer of liquid atoms. The present work examines the rotation of nanoparticles and absorption layer, which is the basis of understanding heat transfer mechanism in nanofluids and proposing mathematical description for the transfer process.