ABSTRACT
Problems involving mass transport, and the solution and analysis of such problems, almost always require the formulation of a mathematical model of the process. The term model, as used here, refers to the equation, or set of equations, that describe the physical system or process under consideration. Such models were already encountered, at a modest level, in the solution of Illustration 1.2, Illustration 1.3, and Illustration 1.5. In all three of these examples, a single expression was applied to model the process, which consisted of the fundamental law of diffusion represented by Fick’s law. No other basic equations were required, and we were able to proceed to a solution of the problem without invoking any additional principles.
