H P = 0.0015607 I; T In( Pout/Pin) OP = annual operating cost, $/yr. ;tic fluids, it is reasonable to expect that a diffusion Deborah number can be defined which corresponds to the Deborah number used to characterize flow of polymeric materials. In this paper we propose a Deborah number which can be used to characterize diffusional transport in amorphous polymer-solvent systems and consider the calculation and utilization of this dimensionless group. Deborah number is demonstrated by using this dimensionless group to anticipate conditions under which thicknezs anomalies can be expected in sorption experiments for the atactic polystyrene-pentane system.Investigations of diffusion phenomena in amorphous polymer-solvent systems have shown that it is possible to observe widely differing behavior by traversing a large enough range of temperature, concentration, and polymer molecular weight. Alfrey ( 1965) and Hopfenberg and FriscEi (1969) depicted the different types of diffusional transport of penetrants in higll polymers by utilizing a tcmperature-penetrant concentration diagram. It was later noted (Duda and Vrentas, 1970) that the various regions on this diagram could be distinguished by the ratio of two characteristic times, a cliaracteristic relaxation time for the