Effect of particle shape and size on effective thermal conductivity of packed beds

Effective thermal conductivity (ETC) is one of the most important thermal properties of packed granular materials, and is affected significantly by particle properties. In this work, discrete element method is used to study the effect of particle shape and size on the ETC of packed beds with ellipsoidal particles. The simulated ETC results are verified by experimental data with a good agreement. It is revealed that for coarse particles, the bed ETC increases with aspect ratio of ellipsoids deviating from 1.0. But for fine particles, the effect of aspect ratio becomes less significant. Such an effect is closely related to the difference of packing structures of ellipsoids at different sizes and aspect ratios. The results also reveal that at low particle thermal conductivity, the ETC is not affected much by particle size; at high particle thermal conductivity, the ETC increases with particle size. When bed temperature increases, the ETC increases markedly. The contributions of different heat conduction paths under different conditions are also quantified.