Effective thermal conductivity of disperse materials. I. Compliance of common models with experimental data

The thermal conductivity of packed beds of various materials (metals, ceramics, superhard materials, polymers, etc.) is measured by the steady-state heat flux method at room temperature in air. Powders and granular materials are used, with particle sizes ranging mainly from 50 μm to 1.5 mm, with various particle shapes (debris, pebble, cubo-octahedral single-crystals, regular spheres), the thermal conductivity of the solid ranging widely from 0.15 to 1500 W/(m K). Experimental data and model calculations of the effective thermal conductivity of the bed are compared, including dependences on bed porosity and particle size. Both classical and more recent models are involved, such as the differential effective medium model and those of Raghavan-Martin, Kunii et al., Zehner-Schlunder, Gusarov et al., Hsu et al., Batchelor-O'Brein, and some others, which allow analytical calculations. The adequacy of the models is reviewed in connection with the properties of the disperse materials (particle shape etc.), based on the concepts of the absence or presence of contact thermal conductivity in the bed.