| Summary: | 博士 === 國立成功大學 === 機械工程學系碩博士班 === 95 === This study investigates the thermophysical properties of nanoparticles with various sizes and the structural features and transport properties of nanoparticles suspensions using molecular dynamics simulations with parallel computing technique. The physical properties of nanoparticle in the simulation are including cohesive energy, surface energy, root mean square displacement (RMSD), melting temperature, and thermal conductivity. The composed parameters of nanoparticles suspensions in the simulation contain particle size, particle volume fraction, and temperature. From the simulated results about the thermophysical properties of nanoparticles, there exists a linear relation for the silicon nanoparticles with more than 357 atoms, within which the melting temperature of particle varies inversely as N-1/3, and the melting temperatures for particles with N=281 and 191 are both seen to be higher than the values predicted from linear fitting; the size of the silicon nanoparticle when it approaches its melting temperature is less than when it is in a solid state; the silicon nanoparticle cohesive energy can be fitted to a linear function of 1/d, where d is the particle diameter, and is independent of temperature; the small particle has a heavily reconstructed geometry, which easily generates lattice imperfections; the calculated thermal conductivities of the silicon nanoparticles are lower than that of the bulk by approximately two orders of magnitude, and decreases rapidly as the temperature increases. From the simulated results of the structural features and transport properties of nanoparticles suspensions, an organized structure shell of liquid is formed close to the surface of solid particle and the shell structure formation becomes more pronounced as the particle size is reduced; the suspension stability of nanoparticles is improved as the particle volume fraction is increased; the diffusion coefficient of the water molecules in fullerenes-in-water suspensions varies as a linear function of the fullerene loading, but is independent of the fullerene size; the dispersion of even a very small amount of particles in the base fluid leads to a significant increase in the viscosity enhancement effect, which is more pronounced at a lower temperature; the simulation results for the thermal conductivity enhancement of nanoparticles suspensions are approximately one order of magnitude higher than the predictions from the theoretical modes; the enhanced thermal conductivity of nanoparticles suspensions is most likely attributed to the nature of heat conduction in nanoparticles and an organized structure at the solid/liquid interface, thereby changing the barrier to heat flow between the solid particle and the liquid fluid. Finally, we present several improvement ways of molecular dynamics simulations, and other application of nanoparticles as our future works.
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