Micro-movements of nanoparticles in nanofluids: molecular dynamics simulation

The present work utilizes Molecular Dynamics (MD) method to simulate the micro-movements of nanoparticles in nanofluids. A simulation model of Cu nanoparticle in H₂O base fluid is established with MD method, which contains 26421 simulating particles. The diameter of the spherical nanoparticle is 4 nm. H₂O is modeled to be the base fluid because it is closer to the real situation of nanofluids, and it is easier to examine the influence of temperature on micro-movements of nanoparticles. It is found that the nanoparticles' movements is in high speed and random in directions. The rotational velocities of nanoparticles is in the range of 1×10⁹-1×10¹⁰ rad•s^-1; and the translational velocities of nanoparticles is in the range of 1-10 m•s^-1. When applying different temperatures, the velocity and temperature distributions of nanofluids are found to be different from single-phase base fluid. The main difference of nanofluids and base fluids is located at the near wall region. Both the velocity gradient and temperature gradient are larger than those of single-phase base fluid. The main reason for the different velocity distributions between nanofluids and base fluid is the random micro-motions of nanoparticles. Furthermore, the changed velocity characteristics influence the heat transfer process, which makes the temperature distribution of nanofluids is different from that of base fluid. Moreover, the temperature distribution of nanofluids changes a lot with the simulation, which can also distributed to the random micro-movements of nanoparticles in base fluid.