(258c) Turbulent Confined Swirling Flow in a Microscale Multi-Inlet Vortex Reactor

The turbulent confined swirling flow in a microscale multi-inlet vortex reactor
(MIVR) is investigated by means of microscopic particle image velocimetry (μ-PIV)
as well as computational fluid dynamics (CFD). The multi-inlet vortex is designed in
hope of providing fast and homogeneous mixing that is essential in production of
nanoparticles via Flash Nanoprecipitation (FNP). Both Reynolds-averaged
Navier-Stokes (RANS) and large-eddy simulations (LES) are carried out to simulate
the velocity fields for three different jet Reynolds numbers, i.e., Re_j = 53, 93 and 240.
The first two Reynolds numbers represent laminar and transition flow regime,
whereas the last one is turbulent. For Re_j = 240, numerical predictions are validated
against μ-PIV measurements. Comparisons show the RANS method with the
widely-used standard k–ε turbulence model underpredicted the mean velocities. LES
with the Smagorinsky model, on the other hand, compares well with experimental
results. Features of the confined swirling flow are examined from the LES by
looking at the axial velocities and streamlines. By computing the λ₂ values,
the vortex cores are extracted. A great amount of vortices are observed
at the contraction where the fluid exits the mixing chamber. In addition
to the turbulent motions in the mixing chamber, the vortex breakdown in
the outlet channel is also key to promoting the mixing performance of the
reactor.