Heat Transport In Nanoparticle And Nanoporous Media And Nanoscale Liquid Flow

The development of research on porous media and the continuing demand for porous media applications in high-tech industries are pushing the research of heat and mass transfer in micro- and nanoscale porous media. The present dissertation investigates the nanoparticle thermal conductivity, nanoscale thermal contact resistance, nanoscale porous media thermal conductivity and nanoscale flow using molecular dynamics (MD) analyses, theoretical analyses and experiments.Two thermal conduction models were constructed for cubical and spherical nanoparticles for non-equilibrium molecular dynamic (NEMD) simulations to investigate the variations of the nanoparticle thermal conductivity with particle size and shape. The simulation results accurately represent the thermal conductivity of argon nanoparticle. The EAM potential model was used to simulate the phonon heat conduction in nickel nanoparticles with the effective thermal conductivity of nickel nanoparticles was found by adding the electronic thermal transport. The simulation results also accurately represent the thermal conductivity of nickel nanoparticles.Two models were used to simulate the thermal conduction across micro contact points and the thermal contact resistance using NEMD simulations with consideration of the near field radiation. The MD results show that the thermal contact resistance quickly increases with decreasing area of the micro contact point and increases with increasing micro contact layer thickness. The simulation results can be used to predict the nanoscale thermal contact resistance as a function of the contact point area and thickness.To analyze the heat transfer in micro- and nanoscale porous media, the macroscale porous media thermal conductivity models were modified to account for the micro- and nanoscale effects in porous media based on the research results for the nanoparticle thermal conductivity and the nanoscale thermal contact resistance. Comparison of the effective thermal conductivities of two nickel nanoparticle packed beds and a microparticle packed bed were measured using the Hot Disk with the calculated results shows that the revised models can accurately predict the effective thermal conductivities of micro- and nanoparticle packed beds.Liquid flow in nanoscale channels was also simulated using the MD method. The simulations show that the wettability between the liquid and the channel surface only affects the velocity gradient in the liquid close to the surface and the velocity where the steep wall velocity gradient transitions to the quadratic velocity profile in the main flow region. The liquid velocity near the channel surface is still zero for these conditions. When the driving force exceeds a critical value the liquid flow is no longer Poiseuille flow. The velocity profiles can be charactered by a slip length which is related to the force between the solid wall and the fluid. Solid wall surface bowing can affect the wall surface characteristic and change the slip length, but has very little effect on the liquid particle number density distribution. Finally, the effect of the cross-sectional variation on the fluid flow in nanochannels weakens rapidly with distance from the variable cross-sectional part of the nanochannel. A preliminary experimental study of water flow in nanopores gave a slip length for de-ionized water in a 240 nm average diameter hydrophilic pore of -17.8～-19.1 nm.