A generalized thermal conductivity model for nanoparticle packed bed considering particle deformation

Theoretically understanding the thermal conductivity of the nanoparticle packed beds (NPBs) is critical for designing high-performance thermal insulation materials. Currently, the classical effective medium assumption (EMA) model, Nan model, just show their good prediction at a high porosity of NPBs (≥0.75). Herein, we propose a generalized model of the thermal conductivity that almost covers the whole porosity range by considering the effect of the nanoparticle deformations on the thermal contact resistance (R). It has been demonstrated that our model matches the experimental results great well. It is also found that at high porosity R is dominated by the phonon diffusive scatterings (Rcd), while it is determined by the phonon ballistic scatterings (Rcb) at a low porosity. More interestingly, R can determine the porosity at which the lowest thermal conductivity of NPBs appears. This work opens a new way to design the desired thermal insulation materials.