Rotor-stator mixers (RSMs) are widely used for emulsification and mixing. However, relatively little is known about the relationship between RSM design, hydrodynamics and performance. Previous studies have investigated shaft power draw as a function of design. However, power draw alone is not sufficient to predict efficiency. In order to understand the effect on performance it is important to investigate how the local turbulent stress is influenced by design parameters. This study investigates the effect of stator slot width on the local dissipation rate of turbulent kinetic energy using particle image velocimetry coupled with a sub-resolution modeling approach suggested in previous studies. Results are compared to traditional shaft power draw measurements and a set of emulsification experiments. It is concluded that wider slots, although requiring less total shaft power, provide a higher maximal (time-averaged) dissipation rate of TKE, which explains why they give rise to more efficient drop breakup. Apparently, more of the power input is transformed into pumping for the narrower slots which leaves less energy for turbulent dissipation. The study illustrates the need for supplementing traditional power draw measurements with local flow characterization in order to better understand the relationship between RSM hydrodynamics and dispersion performance. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.