The performance of a membrane emulsification unit, using flat membranes in a stirred tank, has been examined by dimensional analysis. The dimensionless numbers were defined in terms of shear and membrane pore size. Dimensionless droplet size prediction models based on simple force balances were used to select the most representative dimensionless numbers including operating parameters. Oil-in-water emulsions were produced with tailor-made metallic membranes with pore sizes of 30 and 50 mu m. Results showed that monodisperse emulsions were produced with span values around 0.5, significantly lower than when a rotor-stator homogenizer is used. The influence of the selected operating parameters (impeller rotational speed, continuous phase viscosity and dispersed phase flux) on droplet size distribution was studied and experimental results were compared with droplet size prediction models. Impeller rotational speed and membrane pore size were the key parameters influencing emulsion droplet size and monodispersity. A correlation based on the Euler dimensionless number, including all the operating parameters is proposed. (c) 2013 Elsevier B.V. All rights reserved.