Nonsource Problems

Nonsource problems are by far the most prevalent type of problem involving diffusional processes, and almost all e material contained in standard monographs on diffusion is devoted to this topic. A parallel situation exists in the related field of heat conduction. 

Mention was already made of the variety of geometries and boundary conditions that can arise in these problems, and we proposed to limit ourselves to the semi-infinite, parallel plane, spherical, and cylindrical geometries subject to constant initial and surface concentrations. We start with the simplest of these geometries, the semi-infinite medium, and follow this with a discussion of the other three principal geometries. 

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Transient diffusion in a semi-infinite domain, into a solid bounded by parallel planes, in a sphere, and in the radial direction of a cylinder. The domain is assumed to be initially uniformly loaded or uniformly clean, and to have a constant surface concentration. We term these Nonsource Problems. Occasional departures from the stated assumptions are noted as they occur. 

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