Critical times in multilayer diffusion. Part 2: Approximate solutions

Traditional averaging methods for multilayer diffusion give inaccurate approximations of critical time behaviour, such as the heating time of a material. In particular, they fail to capture the importance of layer order. We use a perturbation expansion of an exact solution to find a simple approximate solution which accurately describes the critical time for transport across multiple layers. This approximate solution is then used to find a correction for the averaging method which captures the key critical time behaviour.