A Limiting Case of Diffusion in a Composite Medium

The diffusion eigenstates of a fluid-filled porous medium with perfect absorption at the pore/matrix interface are shown to be closely connected to the eigenstates of another diffusion problem, where there is no absorption but diffusion can occur in both the pores and the matrix, and the matrix diffusion coefficient tends to ∞. This leads to a new approach for calculating the diffusion eigenstates in the case of perfect absorption at the interface.