Thermophysical Properties Of Nanoparticle Packed Bed

As one of typical nanomaterial,nanoparticle is widely applied in the thermal insulation and thermo-electric or photo-electricity field.The thermal physical properties are of great importance for fundamental and engineering systems.In this thesis,the thermal conductivity and specific heat capacity of nanoparticles and NPBs have been studied with a theoretical and experimental approach to reveal the structure-function relationship between the arrangement or morphology of nanoparticles and thermal physical properties of NPBs.There has been consensus that the specific heat capacity of nanoparticles has size effect predominantly.However,three problems are still exhibiting.(1)Previous researches are focused on the specific heat capacity of nanofluid,there is little research exploring the specific heat capacity of nanoparticles.(2)The specific heat capacity of nanoparticles is mainly studied by the experimental approach,there is little specific heat capacity model for nanoparticles.(3)In current stage,the experimental research about the specific heat capacity of nanomaterial is carried out in the ideal environment without considering the influence of surface adsorption,pressure and interface on the specific heat capacity of nanoparticles.In this study,the specific heat capacity model for the nanoparticles,hollow nanoparticles and core-shell nanoparticles are established based on the continuity media hypothesis and the Lindemann criterion,and the experimental measurement(Differential Scanning Calorimetry method)is carried out to verify the theoretical model.The influence of surface adsorption water and surface oxidation on the specific heat capacity of nanoparticles is also investigated by the DSC method without protective atmosphere.Additionally,the influence of pressure,porosity and interface on the specific heat capacity of nanoparticles is also researched.The thermal conductivity of NPBs have been extensively studied,however,there are still several problems in the thermal conductivity research of NPBs including(1)The error between the thermal conductivity of NPBs and that predicted by the nanoporous thermal conductivity model cannot be neglected due to the large interface area in NPBs caused by the plastic deformation of nanoparticles;(2)Previous research focused on the gas-solid coupling thermal conductivity of NPBs,however,the structure-activity relationship between the nanoparticles arrangement or microstructure in NPBs and thermal conductivities is still in blank;(3)The electric thermal conductivity and phonon thermal conductivity can be separated out from effective thermal conductivity under the strong magnetic field,however,it is very difficult to be applied in practice,inventing a simple and effective way is necessary.In this paper,firstly,establishing the effective thermal conductivity model for NPBs with large porosity(porosity≥90 %)and verifying the theoretical model with the experimental approach.Secondly,the solid phase thermal conductivity model,limited thermal conductivity model and radiation thermal conductivity model of NPBs(porosity≤90 %)are established based on the interface elasticity modulus theory,and an experimental way is applied to verify the theoretical model.Thirdly,the electric thermal conductivity and phonon thermal conductivity detachment model is established based on the Sommerfeld electric gas theory,and the Wiedemann-Franz law is proved invalid for NPBs.Finally,the influence of porosity,pressure,sintering treatment and second-phase nanoparticle doping on the thermal conductivity of NPBs is studied,and presenting the effective and simple way to regulate the thermal conductivity of NPBs.Additionally,the thermoelectric performance and mechanism properties are also characterized.