Scalar transport in inline mixers with spatially periodic flows

Abstract

Spatially persisting patterns form during the downstream evolution of passive scalars in three-dimensional (3D) spatially periodic flows due to the coupled effect of stretching and folding mechanisms of the flow field. This has been investigated in many computational and theoretical studies of 2D time-periodic and 3D spatially periodic flow fields. However, experimental studies, to date, have mainly focused on flow visualization with streaks of dye rather than fully 3D scalar field measurements. Our study employs 3D particle tracking velocimetry and 3D laser-induced fluorescence to analyze the evolution of 3D flow and scalar fields and the correlation between the coherent flow/scalar field structures in a representative inline mixer, the Quatro static mixer. For this purpose an experimental setup that consists of an optically accessible test section with transparent internal elements accommodating a pressure-driven pipe flow has been built. The flow and scalar fields clearly underline the complementarity of the experimental results with numerical simulations and provide validation of the periodicity assumption needed in numerical studies. The experimental procedure employed in this investigation, which allows studying the scalar transport in the advective limit, demonstrates the suitability of the present method for exploratory mixing studies of a variety of mixing devices, beyond the Quatro static mixer.

Numerical Study of Viscous Fluid Flows in a Kenics Static Mixer

“…A satisfactory agreement is also obseved between our predicted results and the correlation of Grace [21].…”

“…In this paper, we studied the influence of Reynolds number, fluid viscosity, aspect ratio and the number of helical elements on the flow patterns and pressure drop. It was found that the CFD results of pressure drop were similar to the literature data (the numerical simulation of Saatdjian et al (2012) and the correlation of Grace (1971)).…”

“…In this paper, the study of viscous Newtonian fluids through a Kenics static mixer was performed via numerical simulation. The reliability of our results was checked by the comparison of the pressure drop as function of Reynolds number againt the numerical simulation of Saatdjian et al [20] and the correlation of Grace [21] and a good agreement was observed. The comparison of velocity fields revealed clearly that the fluid viscosity and Reynolds number have an important impact on the performance of a static mixer.…”

Lagrangian Transport and Chaotic Advection in Three-Dimensional Laminar Flows

“…Here the transverse flow is driven by viscous drag exerted by a rotating outer cylinder via apertures in the stationary inner cylinder (Fig. 6(a)); the cell-wise reorientation angle Θ following (10) is the angular offset of consecutive apertures accomplishes systematic 8 Flow in such devices normally settles on a repeated pattern and thus effectively becomes periodic after a short transient following the inlet [84]. The RAM is inspired by the Partitioned-Pipe Mixer (PPM) shown in Fig.…”

“…Fig. 11 demonstrates the transverse mixing within each duct segment by horizontal and vertical splitting (and subsequent recombination) of the axial throughflow by the central plates of elements 1 and 2, respectively, via the 3D streamline pattern measured with 3D Particle Tracking Velocimetry (3DPTV) [94,84]. Mixing element 1 splits the incoming fluid into two separate streams (indicated in red and green) that, in turn, undergo further splitting by element 2, resulting in a "mixture" of red and green streamlines at the segment exit.…”