Micromixing characterisation in rapid mixing devices by chemical methods and LES modelling

Abstract : The work reported here describes a Computational Fluid Dynamics (CFD) modelling of micromixing using the Large Eddy Simulation (LES) approach. Two models are proposed in order to define the micromixing time constant from the LES parameters. The modelling is applied to study mixing efficiency in three high-intensity mixers of the same family and commonly used: T-shaped tube, Y-shaped tube with a 90 angle and Hartridge–Roughton mixing device. Micromixing is also experimentally investigated using two chemical methods, the ‘‘iodide–iodate’’ micromixing test reaction and an acid–base neutralization test. Micromixing time values determined by both methods lead to the same mixer classification, the Hartridge–Roughton configuration being much more efficient than the two other ones. Numerical results are consistent with experimental ones, which validates the LES micromixing models developed. The analysis of the flow field and the turbulent structures inside the three mixers shows that the Hartridge– Roughton tube is characterised by a high rotating central structure whereas, contrary to the Y-shaped tube which reveals a very weak presence of turbulent structures.