Transient and Anisotropic Properties of Diffusive Transport in Spatially Periodic Media

Anisotropic and transient diffusion in spatially periodic and heterogeneous media is formulated. Based on the formulation, a method of numerical calculation is proposed as a useful tool in the design and analysis of heterogeneous materials. This method is applied to several binary systems including a honeycomb structure and a square grid with ellipsoidal filler. Calculation results strongly suggest that transient diffusive behaviour, which can be observed in some experimental systems, should be important to elucidate the internal structure of a heterogeneous medium. The time scale of this transient property of thermal diffusion in practical composite materials is estimated using a physical constant of polyethylene; it proved to be of the order of magnitude which is quantitatively detectable by experimental means.