Finite difference procedures for evaluating the conduction of heat and diffusion of substances in a solid layer or film.

With the advent of the digital computer, complex problems associated with the slow transport of substances and heat by diffusion could be readily solved by finite difference methods. This paper describes the methods used to solve the basic differential equation for diffusion using the examples of heat conduction in a road structure under solar radiation, evaporation of a volatile diluent from a sprayed film of bitumen and the diffusion controlled reaction of atmospheric oxygen with the bitumen films in pavement surfacings. The methods are tolerant of limited changes in the length of the diffusion path with time and two applications where this was used are described. Papers and reports by the author where the methods were applied are referenced. (a).