Analytical model for the thermal conductivity of a binary bed of packed spheroids in the presence of a static gas, with no adjustable parameters provided contact conductance is negligible

A model is given for the thermal conductivity of uncompressed, binary, packed-pebble beds of small and large solid spheroids in a static gas. It requires no adjustable parameters if the conductance of the solid is much greater than that of the gas, and the heat flow through the physical contacts between spheres is negligible compared to that from either gaseous conduction or radiation. The model is in excellent agreement with experiment, provided one assumes there is an average gas gap next to the large spheres, of width about 0.7 of the radius of a small particle.