A rapid precipitation process to produce nanoparticles requires customized devices to achieve fast mixing and homogeneous aggregation kinetics. These microscale devices, such as confined impinging jet (CIJ) reactor and multi-inlet vortex (MIV) reactor, were selected due to their capacity of producing highly turbulent flow and therefore good mixing. An MIV reactor is of great interest in terms of its flexibility since it does not require equal momenta for each inlet as with CIJ reactors. The mixing performance of a MIV reactor has been studied [1] using computational fluid dynamics (CFD) by applying a parallel-reaction system, and the results agreed well with experimental data.

In order to have a fundamental understanding of the fluid dynamics and scalar mixing in the MIV reactor, and to validate the computational models, microscale particle image velocimetry (microPIV) experiments and detailed flow simulations have been performed. The instantaneous velocity field in the MIV reactor is measured using microPIV for inlet Reynolds number ranging from 100 (laminar flow) to 1000 (turbulent flow) at different locations of the reactor. The velocity data are analyzed for flow statistics such as the mean velocity, Reynolds stresses, turbulent kinetic energy, and turbulent dissipation rate. The experiment results are compared with large-eddy and direct-numerical simulations to improve the computational models. In particular, the transitional region from laminar to turbulent flows is important to capture correctly because it represents the best compromise between good scalar mixing and overall pressure drop.

[1] Ying Liu, Chungyin Cheng, Ying Liu, Robert K. Prud'homme and Rodney O. Fox , Mixing in a Multi-Inlet Vortex Mixer (MIVM) for Flash NanoPrecipitation, Chemical Engineering Science (in press), 2008