THERMAL CONDUCTIVITY OF POROUS MATERIALS: I. THEORETICAL TREATMENT OF CONDUCTION PROCESSES.

The theoretical background relating to thermal conduction in porous materials is discussed and extended to interpret these processes more rigorously. It has been shown that the most conventional models can be derived from a set of general equations adapted from electrical theory. The general model takes into account the shape and orientation of pores (or inclusions) as well as the thermal conductivities and volume fractions of the component phases. The effect of shape and orientation has been examined and shown to be a major influence on the conductivity of composite materials. Improvement of the performance of thermal insulants by entraining suitably shaped inclusions is discussed.