Effective Thermal Conductivity Within Packed Beds of Spherical Particles

An investigation of the effective thermal conductivity of packed beds of spherical particles was conducted. Included is a brief review of related analytical and experimental investigations, along with a description of the results from an experimental program. Five beds of different materials were evaluated to determine the effective thermal conductivity as a function of the mechanical load on the bed, the conductivity of the bed material, and the interstitial gaseous environment surrounding the bed particles. The effective thermal conductivity of the packed beds were found to be dependent upon the thermal conductivity of the bed material and the axial load. The presence of an interstitial gas increased the effective thermal conductivity of the bed by a factor of two in almost all cases. The experimental results obtained for vacuum conditions were compared with two existing analytical models that assumed elastic deformation of the spheres. The analytical models slightly under-predicted the effective thermal conductivity for hard materials with low thermal conductivities below the elastic limit, and slightly overpredicted the effective thermal conductivity above the elastic limit for these materials. For soft materials with relatively high thermal conductivities, the analytical models overpredicted the effective thermal conductivity by as much as an order of magnitude.