For the first time, the mass transport phenomenon in pervaporation of the ethanol/water system via PVDF asymmetric hollow fiber membranes has been demonstrated through the pore-flow model and a newly modified pore-flow model has been proposed The modified pore-flow model differs from the pore-flow model by factoring in the contribution of Knudsen flow to vapor transport, which was Ignored by the pore-flow model The correlation of transport parameters to membrane pore size is explored and it is found that the pore size expansion (including the change of membrane surface morphology) is strongly dependent on the solvent in contact. The modified pore-flow model shows a better prediction for the permeate composition than the pore-flow model and both models exhibit an excellent prediction of total permeate mass flux The significance of Knudsen flow contribution in vapor-phase transport as stated in the modified pore-flow model is discussed from the experimental and theoretical aspects (C) 2010 Elsevier B.V All rights reserved