The assumptions of the traditional shrinking core model cannot be adopted for the core shell structure formed during the reaction of aluminum particles and water. The model assumes that diffusion coefficient is constant and the particle size is unchanged during the reaction. This study modifies the traditional shrinking core model by including the effect of the growing size of the particles and the changes in porosity of the hydroxide layer on hydrogen generation. The modified model is fitted to the experimental data and the results are compared to that of the traditional model. The flux of water molecules in the hydroxide layer is calculated using the parameters obtained by the hydrogen generation data. (C) Copyright 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.