Pressure driven membrane filtration processes have emerged as cost effective and confirmed technologies. Ultrafiltration is used to produce drinking water. Hollow fiber membranes are used in industrial processes but there is still a need of predicting pressure drops for design and optimization purposes: to control the production of water, to anticipate problems such as the clogging of the hollow fibers and/or the module position and to consider energy consumption. This prediction could also enhance current models that calculate pressure drop using the Hagen-Poiseuille law. In this work, the flow characteristics controlling the performance of a hollow fiber membrane module are investigated numerically. The aim of this study is to determine the pressure drop in a module depending on the operating conditions and membrane characteristics: a simplified model equation is proposed. We use a commercial CFD package (FLUENT). Numerical simulation can provide a better understanding of module performance, especially for permeable wall and/or complex multi-component systems. CFD can be used to better apprehend fluid flows in complex geometries and to test the influence of process parameters. The results are compared to experimental data obtained with an industrial pilot plant: a good agreement with our relation is obtained. (c) 2006 Elsevier B.V. All rights reserved.