Turbulent mixing in the confined swirling flow of a multi-inlet vortex reactor

Turbulent mixing in the confined swirling flow of a multi-inlet vortex reactor (MIVR) was investigated using planar laser induced fluorescence (PLIF). The investigated Reynolds numbers based on the bulk inlet velocity ranged from 3290 to 8225, and the Schmidt number of the passive scalar was 1250. Measurements were taken in the MIVR at three different heights (1/4, 1/2, and planes). The mixing characteristics and performance of the MIVR were investigated using instantaneous PLIF fields and pointwise statistics such as mixture fraction mean, variance, and one-point concentration probability density function. It was found that the scalar is stretched along velocity streamlines, forming a spiral mixing pattern in the free-vortex region. In the forced-vortex region, mixing intensifies as the turbulent fluctuations increase significantly there. The mixing mechanisms in the MIVR were revealed by identifying specific segregation zones. At Re=8225 the mixing in the free-vortex region was dominated by both large-scale structures and turbulent diffusion, while in the forced-vortex region mixing is dominated by turbulent diffusion. (c) 2016 American Institute of Chemical Engineers AIChE J, 63: 2409-2419, 2017