A model for the design of a wiped film evaporator (WFE) for the devolatilisation of polymer solutions is presented. Unlike previous models, the one presented in this paper considers both the fluid transport and mass transfer aspects of the problem. Analysis of the results indicates that neglecting the limitations imposed by the equilibrium concentration of the volatile species in the problem formulation leads to the underestimation of the device size required to obtain a given purity. This is especially true when the equilibrium concentration and final purity are of the same order of magnitude. As is expected, the devolatilising capacity of the WFE increases as the speed with which its wiper blades remix the film increases. However, it appears that there is limiting rotational speed for mixing in the WFE, above which significant gains in mass transfer are obtained at the expense of very large increases in power consumption. The results of the design model agree well both qualitatively and quantitatively with data published on commercially available WFEs.