As in the application of radiation shields discussed in Section 4.4.5, there are applications where the surface-radiation through multiple (thin, opaque solid) layers (or solid slabs) is of interest. This is rendered in Figure Pr. 4.16, where these layers are placed between surfaces maintained at Th and Tc. Since for large N (number of layers) the local radiation heat transfer becomes independent of the presence of the far-away layers, we can then use the local (or diffusion) approximation of radiation heat transfer and use the temperature difference (or local temperature gradient) between adjacent layers and write
