Water permeability of a multi-tube Nafion membrane module is determined and compared with that of a single-tube module. The membranes of the two modules are made of the same materials but have different thicknesses. Anomalous thickness effects were observed for the Nafion membranes. Water permeability per unit thickness increased with increasing membrane thickness. This phenomenon is quantitatively described here as a skin effect or interfacial resistance.Simulations were performed for the multi-tube membrane module using the model developed in the first part of this paper. After considering the skin effects, the model predictions matched experimental data well over a wide range of operating conditions. In most cases, the absolute errors between the predicted products' relative humidity and the experimental values are within +/-2%, and the relative errors are less than 15%. Mass transfer resistances along the membrane module and the relationship between the membrane length and its drying performance under some typical operating conditions were also analyzed. (C) 2003 Elsevier B.V. All rights reserved.