Rotor-stator mixers are used in many industries to perform emulsification and de-agglomeration processes. Despite previous research, different modes of operation have not been compared in terms of flow and power characteristics. The aim of this study was to use CFD to investigate power and flow characteristics of a Silverson L5M mixer operating in batch and in-line mode. MRF was used along with the standard k - epsilon turbulence model for the simulations. Results suggest that batch mixers can be characterised in the same was as in-line mixers, and for a given mixing head design, the characterisation is independent of the mode of operation. A new way of the calculating flow number is proposed, which explains some discrepant results from previous studies. Overall, this work enhances our understanding of rotor-stator mixers and allows for better design choices of mixer. (C) 2019 Elsevier Ltd. All rights reserved.