A COMPARISON OF 2 METHODS FOR SOLVING TRANSPORT-EQUATIONS WITH WEAK DIFFUSION

The equations that describe the transport of material through a separa tion system often take the form of diffusion-convection equations in w hich diffusion plays a minor role. It is possible to derive approximat e solutions to such equations using singular perturbation theory. At l east two such theories have been developed, one by van Kampen and the second by Weiss and Dishon. We compare results generated by the two th eories on two exactly solvable equations, one equivalent to the Lamm e quation and the second related to electrophoresis in a gradient. In bo th cases the van Kampen approximation proved to be more accurate in a neighborhood of the peak for a pulse-loaded system.