Micro-mixing characteristics of a pinched-tube, a fluidic oscillator and a vortex-based cavitation device

Micro-mixing plays a crucial role in controlling performance and quality of products from anti-solvent crystallization, reactive precipitation and nanoparticle synthesis. In this work, micro-mixing was characterised using the Villermaux Dushman iodide-iodate reactions in three fluidic devices namely a pinched-tube, a fluidic oscillator and a vortex-based cavitation device operated in a loop configuration. A three-environment engulfment model was developed to simulate mixing and reactions in these devices operated in a flow loop. The loop was operated at different flow rates to cover a broad range of energy dissipation rates (ε= ∼ 10⁻¹–10⁴ W/kg) with the three devices. The considered fluidic devices exhibited micro-mixing times in the range of 28–160 ms. The micro-mixing times estimated from the engulfment model were found to be proportional to ε^-0.17. Among the investigated devices, the fluidic oscillator had the lowest micro-mixing time of ∼28 ms. The pinched tube exhibited a micro-mixing time in the range of 30–74 ms while the vortex-based cavitation device exhibited a micro-mixing time in the range of 33–80 ms before the inception of cavitation. For the conditions where cavitation occurred in the vortex-based cavitation device, the usual method of estimation of micro-mixing time was not suitable since oxidising radicals generated by cavitation interfere with the Villermaux Dushman reactions. The presented model, data and discussion will be useful for selecting appropriate fluidic devices for mixing applications and further work on characterising mixing in cavitation devices.