• non-Newtonian fluid;
  • proper orthogonal decomposition;
  • mixing;
  • particle image velocimetry;
  • stirred tank;
  • shear rate;
  • dissipation

The local shear rate generated in a cylindrical tank equipped with a Rushton turbine was investigated using particle image velocimetry in a shear-thinning fluid (Carbopol). This non-Newtonian fluid was used in an attempt to mimic fermentation broths. Three Reynolds numbers corresponding to the transition regime were investigated. The hydrodynamics is analyzed, and the velocity field is decomposed by proper orthogonal decomposition into mean flow, organized motion, and turbulence. Then, the contributions of each flow structure to the total dissipation of kinetic energy are presented. The spatial heterogeneity of shear rate is discussed and a new expression is proposed for shear rate. This work shows that the local shear rate is highly heterogeneous in a tank. Future works will need to focus on other types of stirrer and investigate the effect of scaling up reactors on the shear rate heterogeneity. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2251–2266, 2013