Effect of Vertical Vibration on the Mixing Time of a Passive Scalar in a Sparged Bubble Column Reactor

The present study used a sparged bubble column to study the mixing of a passive scalar under bubble-induced diffusion. The effect of gas superficial velocity (up to 69 mm/s) and external vertical vibrations (amplitudes up to 10 mm, frequency <23 Hz) on the mixing time scale were investigated. The bubble-induced mixing was characterized by tracking the distribution of a passive scalar within a sparged swarm of bubbles. Void fraction and bubble size distribution were also measured at each test condition. Without vibrations (static), the bubble column operated in the homogenous regime and the mixing time scale was insensitive to void fraction, which is consistent with the literature. In addition, the temporal evolution of the static column mixing was well approximated as an error function. With vertical vibrations at lower amplitudes tested, the bubble-induced mixing was restrained due to the suppression of the liquid velocity agitations in the bubble swarm wake, which decelerates mixing. Conversely, at higher amplitudes tested, vibration enhanced the bubble-induced mixing; this is attributed to bubble clustering and aggregation that produced void fraction gradients, which, in turn, induced a mean flow and accelerated the mixing. The vibration frequency for the range studied in the present work did not produce a significant effect on the mixing time. Analysis of the temporal evolution of the concentration of the passive scalar at a fixed point within the column revealed significant fluctuations with vibration. A dimensionally reasoned correlation is presented that scales the non-dimensional mixing time with the transient buoyancy number.

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MMC-LES of a syngas mixing layer using an anisotropic mixing time scale model

Combustion and Flame ◽

10.1016/j.combustflame.2017.11.004 ◽

2018 ◽

Vol 189 ◽

pp. 311-314 ◽

Cited By ~ 4

Author(s):

Son Vo ◽

Andreas Kronenburg ◽

Oliver T. Stein ◽

Matthew J. Cleary

Keyword(s):

Time Scale ◽

Mixing Time ◽

Mixing Layer ◽

Scale Model ◽

Mixing Time Scale

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Effect of Amplitude on Mass Transport, Void Fraction and Bubble Size in a Vertically Vibrating Liquid-Gas Bubble Column Reactor

10.1115/fedsm2013-16116 ◽

2013 ◽

Author(s):

A. L. Still ◽

A. J. Ghajar ◽

T. J. O’Hern

Keyword(s):

Mass Transport ◽

Void Fraction ◽

Bubble Size ◽

Bubble Column ◽

Bubble Column Reactor ◽

Gas Bubble ◽

Column Reactor

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The velocity and mixing time scale of the Arctic Ocean Boundary Current estimated with transient tracers

Journal of Geophysical Research Atmospheres ◽

10.1029/2009jc005965 ◽

2010 ◽

Vol 115 (C8) ◽

Cited By ~ 12

Author(s):

A. Mauldin ◽

P. Schlosser ◽

R. Newton ◽

W. M. Smethie ◽

R. Bayer ◽

...

Keyword(s):

Arctic Ocean ◽

Time Scale ◽

Mixing Time ◽

The Arctic ◽

Boundary Current ◽

The Arctic Ocean ◽

Ocean Boundary ◽

Mixing Time Scale

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Transport and instability in driven two-dimensional magnetohydrodynamic flows

Journal of Fluid Mechanics ◽

10.1017/jfm.2016.361 ◽

2016 ◽

Vol 799 ◽

pp. 541-578 ◽

Cited By ~ 2

Author(s):

Sam Durston ◽

Andrew D. Gilbert

Keyword(s):

Magnetic Field ◽

Time Scale ◽

Large Scale ◽

Body Force ◽

Passive Scalar ◽

Fast Time ◽

Two Dimensional ◽

Mean Flow ◽

The Mean ◽

Background Shear

This paper concerns the generation of large-scale flows in forced two-dimensional systems. A Kolmogorov flow with a sinusoidal profile in one direction (driven by a body force) is known to become unstable to a large-scale flow in the perpendicular direction at a critical Reynolds number. This can occur in the presence of a ${\it\beta}$-effect and has important implications for flows observed in geophysical and astrophysical systems. It has recently been termed ‘zonostrophic instability’ and studied in a variety of settings, both numerically and analytically. The goal of the present paper is to determine the effect of magnetic field on such instabilities using the quasi-linear approximation, in which the full fluid system is decoupled into a mean flow and waves of one scale. The waves are driven externally by a given random body force and move on a fast time scale, while their stress on the mean flow causes this to evolve on a slow time scale. Spatial scale separation between waves and mean flow is also assumed, to allow analytical progress. The paper first discusses purely hydrodynamic transport of vorticity including zonostrophic instability, the effect of uniform background shear and calculation of equilibrium profiles in which the effective viscosity varies spatially, through the mean flow. After brief consideration of passive scalar transport or equivalently kinematic magnetic field evolution, the paper then proceeds to study the full magnetohydrodynamic system and to determine effective diffusivities and other transport coefficients using a mixture of analytical and numerical methods. This leads to results on the effect of magnetic field, background shear and ${\it\beta}$-effect on zonostrophic instability and magnetically driven instabilities.

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Mixing Time Scale Determination in Microchannels Using Reaction Calorimetry

Chemie Ingenieur Technik ◽

10.1002/cite.201800169 ◽

2019 ◽

Vol 91 (5) ◽

pp. 622-631 ◽

Cited By ~ 2

Author(s):

Felix Reichmann ◽

Kai Vennemann ◽

Timothy Aljoscha Frede ◽

Norbert Kockmann

Keyword(s):

Time Scale ◽

Mixing Time ◽

Reaction Calorimetry ◽

Mixing Time Scale

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Mixing Time Scale Measurement With Fast Exothermic Reactions Using Microchannel Reaction Calorimetry

ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2018-7627 ◽

2018 ◽

Author(s):

Felix Reichmann ◽

Yannick Jirmann ◽

Norbert Kockmann

Keyword(s):

Heat Flux ◽

Time Scale ◽

Mixing Time ◽

Main Reaction ◽

Reaction Calorimetry ◽

Flow Rates ◽

Exothermic Reactions ◽

Reaction Progress ◽

Reaction Calorimeter ◽

Mixing Time Scale

Continuous reaction calorimetry in microreactors is a powerful technology for the investigation of fast and exothermic reactions regarding thermokinetic data. A Seebeck element based reaction calorimeter has been designed, manufactured, and its performance has been shown in previous works using neutralization reaction in a microreactor made from PVDF-foils [1]. The Seebeck elements allow for spatial and temporal resolution of heat flux profiles across the reactor. Therefore, hot spots and regions of main reaction progress are detected. Finally, heat of reaction has been determined in good agreement with literature data [1]. However, more information can be retrieved related to chemical transformations using the continuously operated reaction calorimeter. In this work, mixing time scale is determined for instantaneous and exothermic reactions. Volumetric flow rate is varied and the region of main reaction progress is shifted within the microreactor. The reaction occurs near the reactor outlet for low flow rates. Here, mixing is dominated by diffusion. However, the reaction and hot spot are shifted towards the reactor inlet for high flow rates as convective mixing regime is reached and secondary flow profile with Dean vortices develop due to curvature of the reaction channel. Finally, mixing time scales can be derived from the location of heat flux peaks. Results display a decrease in mixing time at increased flow rates. Additionally, passive micromixers can be evaluated regarding their efficiency and comparison can be drawn. Moreover, pumps can be characterized and evaluated regarding low-pulsation dosing using the Seebeck element based reaction calorimeter.

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