Mechanism Of Transport Properties In Nanofluids By Molecular Dynamics Simulations

Nanofluids, a sort of researching working fluid with nanoparticles inside, havebeen proposed as a route for surpassing the performance of currently available heattransfer liquids in the near future. This dissertation presents reference data, experimentaldata, molecular dynamics simulation results and theroretical analysis of the mechanismof nanofluids transport properties, such as thermal conductivity, viscosity and diffusioncoefficient.The auto correlation function formulas of nanofluids' transport parameters werededuced in this dissertation and a simulation system was established to investigatenanofluids' transport parameters, including thermal conductivity, viscosity anddiffusion coefficient, according to the deduced formulas. According to analysis thestability of the transport parameters integral functions, a new conception was proposed—mean-free-force-path. Combined the mean-free-force-path with related formulas andtheories, a new formula was deduced which used to calculate the time step in moleculardynamics simulations.The nanofluids' dispersivity and stablility were also investigated throughexperiments and simulations. The dispersion stability of nanoparticles indeionized water and refrigerants were investigated by experiments. The suitablepreparation method was summarized and the optimum oscillation time wasdiscussed. Molecular dynamics simulations were used to investigate Brownianmotion of the nanoparticles in base fluid. The absorbed liquid molecular layeraround the nanoparticle and aggregation of nanoparticles were also investigated,and other factors, such as the particle size and temperature, were also discussed.The nanofluids' transport properties, with the base fluid of water or refrigerantR123or R141b, were investigated by combined with reference data, experimental data,molecular dynamics simulations results and theoretical analysis of the mechanism. Mostof the important factors, such as temperature, volume fraction, nanoparticle size,nanoparticle shape, surface area and sphericity, were discussed in the dissertation whicheffect the nanofluids' thermal conductivity and viscosity.A new parameter, TPeV, was introduced to analysis the mechanism ofnanoparticles in the nanofluid and TPeV is the abbreviation of Transport Properties Enhancement Ratio by Nanoparticles Volume Fraction. CombinedTPeV with the reference data, we believe that there exist the best volumefraction and maxium volume fraction of nanoparticles in nanofluid.The collective heat flux vector of nanofluids' thermal conductivity was separatedinto the liquid contribution, the nanoparticles contribution, and the interaction betweenliquid and nanoparticles; the results show that the contribution of the nanoparticles tothe nanofluids' thermal conductivity meet the Maxwell's effective medium theory, butthe liquid parts' thermal conductivity was higher than the fluid with no nanoparticlesitself. The heat flux vector was also decomposed into the kinetic energy, theintermolecular potential, the pair virial function and the interaction between allfunctions; the results show that the most remarkable aspect is the increase ofpotential contribution which plays an insignificant single base fluid. The stresstensor of viscosity can also separated into the liquid contribution, the nanoparticlescontribution, and the interaction between liquid and nanoparticles by work fluids; theresults show that there is little difference of viscosity between Einstein' theory andnanofluids with few nanoparticles volume fraction; when the volume fraction is higherthan a certain value, the effective viscosity become to increase sharply which mainlydue to the changing of fluid's rheology by enough nanoparticles.