Flow regimes and mass transfer characteristics in static micromixers

Kockmann, Norbert; Föll, Claus; Woias, Peter

doi:10.1117/12.478157

Cited by 42 publications

(32 citation statements)

References 10 publications

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“…Using laminar flow the results of former studies on liquid flow [4,11,12] can be confirmed to hold true for gas phase flows. The simulations are based on a three-dimensional T-shaped micro channel geometry for the numerical grid.…”

Section: Fluid Dynamics Simulation Of the Micro-mixersupporting

confidence: 62%

“…To prevent these particle losses, a redesign of the fluid inlet is necessary to avoid such bends and to allow a smooth, co-axial entrance into the mixer. Unfortunately, losses occur also in the mixing region, as seen in figure 8, most likely caused by the formation of vortices in the mixing zone [4], which prevents inertial particles from following the streamlines of these vortices and impacts them on the surrounding walls. The exit of the mixed flow region also shows visual signs of some particle deposition, which is, however, minor compared to the deposits found at the inlet and in the mixing zone.…”

Section: Resultsmentioning

confidence: 99%

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Particle deposition from aerosol flow inside a T-shaped micro-mixer

Heim¹,

Wengeler²,

Nirschl³

et al. 2005

J. Micromech. Microeng.

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A T-shaped micro-reactor was used to mix a particle laden gas stream (an 'aerosol') and a clean gas stream, here with the objective of determining particle losses to the inside walls of the reactor (and hence the potential for clogging) as a function of operating conditions. Losses were determined with established on-line concentration measurement techniques, using monodisperse sodium chloride particles and vitamin-E-acetate droplets of variable size range between 10 and 700 nm. Measured losses range between 10 and 95%, depending on flow rate and particle size, and can be modeled with the particle Stokes number. CFD and particle trajectory modeling confirm that particle impact on the walls of the inlet and the mixing zones is the predominant particle deposition mechanism, induced by the local, sharp curvature of streamlines. The modeling points to ways of optimizing the inlet geometry of the mixer to reduce impaction losses significantly.Reynolds number (−) t time (s) u mean gas velocity (m s −1 ) u gas velocity (m s −1 ) V volume (m 3 ) W probability (−) η dynamic viscosity (kg m −1 s −1 ) λ mean free path of gas (m) ρ density (kg m −3 )

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Section: Fluid Dynamics Simulation Of the Micro-mixersupporting

confidence: 62%

Section: Resultsmentioning

confidence: 99%

Particle deposition from aerosol flow inside a T-shaped micro-mixer

Heim¹,

Wengeler²,

Nirschl³

et al. 2005

J. Micromech. Microeng.

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show abstract

“…Flow regimes in a T-mixer with a rectangular cross section are reported in the numerical study by Kockmann et al (2003). As they increased the Reynolds number, they observed laminar flow, then vortical flow, and then engulfment flow, in which the streamlines in the mixing channel are asymmetric.…”

Section: Introductionmentioning

confidence: 93%

The planar X-junction flow: stability analysis and control

et al. 2014

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The bifurcations and control of the flow in a planar X-junction are studied via linear stability analysis and direct numerical simulations. This study reveals the instability mechanisms in a symmetric channel junction and shows how these can be stabilized or destabilized by boundary modification. We observe two bifurcations as the Reynolds number increases. They both scale with the inlet speed of the two side channels and are almost independent of the inlet speed of the main channel. Equivalently, both bifurcations appear when the recirculation zone(s) reach a critical length. A two-dimensional stationary global mode becomes unstable first, changing the flow from a steady symmetric state to a steady asymmetric state via a pitchfork bifurcation. The core of this instability, whether defined by the structural sensitivity or the disturbance energy production, is at the edges of the recirculation bubbles, which are located symmetrically along the walls of the downstream channel. The energy analysis shows that the first bifurcation is due to a lift-up mechanism. We develop an adjustable control strategy for the first bifurcation with distributed suction/blowing at the walls. The linearly optimal wall-normal velocity distribution is computed through a sensitivity analysis and is shown to delay the first bifurcation from Re = 82.5 to Re = 150. This stabilizing effect arises because blowing at the walls weakens the streamwise velocity gradient around the recirculation zone and hinders the lift-up.At the second bifurcation, a three-dimensional stationary global mode with a span-wise wavenumber of order unity becomes unstable around the asymmetric steady state. Nonlinear three-dimensional simulations at the second bifurcation display transition to a nonlinear cycle involving growth of a three-dimensional steady structure, time-periodic secondary instability, and nonlinear breakdown restoring a two-dimensional flow. Finally, we show that the sensitivity to wall suction at the second bifurcation is as large as it is at the first bifurcation, providing a possible mechanism for destabilization.

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“…Numerous studies [42][43][44][45][46] have shown that fast mixing (in the range of few milliseconds) can be achieved in T-mixers. Indeed, at Reynolds numbers (Re) greater than 400, vortices are created at the T-junction which enhances mixing.…”

Section: Mixing and Flow Propertiesmentioning

confidence: 99%

Aggregation and breakup of acrylic latex particles inside millimetric scale reactors

Lachin

Sauze

Raimondi

et al. 2017

Chemical Engineering and Processing: Process Intensification

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OATAO is an open access repository that collects the work of some Toulouse researchers and makes it freely available over the web where possible. a b s t r a c tAggregation of acrylic latex is investigated inside tubular millireactors working under laminar hydrodynamic conditions. The size distribution and fractal dimension of aggregates are measured using light scattering. Results show that the equilibrium between rupture and aggregation is achieved quickly, allowing the study of cluster size distribution and shape at the aggregation/rupture steady state. Both laminar hydrodynamic conditions and high shear rate are suspected to promote the formation of aggregates with a high fractal dimension, which means that the particles are almost spherical, thereby offering an interesting alternative to conventional batch processes. These results can provide useful information for industries aiming at producing aggregates at specified size and quality.

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Flow regimes and mass transfer characteristics in static micromixers

Cited by 42 publications

References 10 publications

Particle deposition from aerosol flow inside a T-shaped micro-mixer

Particle deposition from aerosol flow inside a T-shaped micro-mixer

The planar X-junction flow: stability analysis and control

Aggregation and breakup of acrylic latex particles inside millimetric scale reactors

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