Theoretical and Experimental Investigations of Convective Micromixers and Microreactors for Chemical Reactions

Dreher, Simon; Engler, Michael; Kockmann, Norbert; Woias, Peter

doi:10.1007/978-3-642-04549-3_18

Cited by 9 publications

(12 citation statements)

References 12 publications

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“…From that point forward, mass transfer is dominated by diffusion only, limiting the maximum mixing efficiency that this conventional mixer can offer. As such, Dreher et al stressed the importance of careful designs of downstream channel to further enhance mixing [15]. Figure 2b shows the corresponding evolution of the mixing index and mixing potential.…”

Section: Resultsmentioning

confidence: 98%

“…Mixing index is defined on a cross sectional plane as Eq. 11 [14,15]. σ 2 represents the concentration variance on the cross section, and σ 2 max is the maximum concentration variance.V 1 denotes the volumetric flowrate of the stream with the tracer, whileV 2 represents the volumetric flowrate of the stream without the tracer.…”

Section: Quantification Of Mixing Efficiency and Mesh Independency Testmentioning

confidence: 99%

“…As the Reynolds number increases from 1 to 240, the flow field varies from strict laminar flow to vortex and engulfment flow. Higher Reynolds numbers lead to unstable flow field [15]. However, Tmixers and Y-mixers with circular channel are commercially available but rarely studied.…”

Section: Introductionmentioning

confidence: 99%

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Rational design of the inlet configuration of flow systems for enhanced mixing

et al. 2021

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High mass transfer rate is a key advantage of microreactors however, under their characteristic laminar flow, it is dominated by slow diffusion rather than fast convection. In this paper, we demonstrate how the configuration of the inlet, i.e. mixers, can promote different flow patterns to greatly enhance mixing efficiency downstream. A systematic evaluation and comparison of different widely adopted mixers as well as advanced designs is presented using a combination of computational fluid dynamics (CFD) and backward particle tracking to accurately calculate diffusion, in the absence of numerical diffusion (false diffusion). In the method, the convection contributed concentration profile is obtained by tracking sampling points from a cross-sectional plane to the inlet point, and diffusion is estimated subsequently. In conventional T- and Y-mixers, the shape of channel, circular or square, is key with only the latter promoting engulfment flow. In cyclone mixers, the resulting average inlet velocity, independent of Reynolds number or geometry, is the dominating design parameter to predict mixing efficiency. This work will serve as a guideline for the design of efficient flow systems with predicted mixing as a way of maximising selectivity and product quality.

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Section: Resultsmentioning

confidence: 98%

Section: Quantification Of Mixing Efficiency and Mesh Independency Testmentioning

confidence: 99%

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Rational design of the inlet configuration of flow systems for enhanced mixing

et al. 2021

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“…For successful implementation of the proposed method, users need to align the tube connection properly, exploit a small syringe or pneumatics for fluid delivery to avoid flow oscillation 23 , use a LED light source to reduce excess heat, conduct the calibration procedure at low Reynolds numbers 24 , and place the microfluidic device in focus to eliminate higher-order optical effects 31 . The lowest measurable gradient (bright pattern, ∂w/∂y < 0) is linked to the dynamic range of the camera, whereas the highest measurable gradient (dark pattern, ∂w/∂y > 0) is reached when the knife-edge completely blocks the deflected light.…”

Section: Discussionmentioning

confidence: 99%

Analyzing Mixing Inhomogeneity in a Microfluidic Device by Microscale Schlieren Technique

Sun

Hsiao

2015

JoVE

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In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren system is constructed from a Hoffman modulation contrast microscope, which provides easy access to the rear focal plane of the objective lens, by removing the slit plate and replacing the modulator with a knife-edge. The working principle of microscale schlieren technique relies on detecting light deflection caused by variation of refractive index [1][2][3] . The deflected light either escapes or is obstructed by the knife-edge to produce a bright or a dark band, respectively. If the refractive index of the mixture varies linearly with its composition, the local change in light intensity in the image plane is proportional to the concentration gradient normal to the optical axis. The micro-schlieren image gives a twodimensional projection of the disturbed light produced by three-dimensional inhomogeneity.To accomplish quantitative analysis, we describe a calibration procedure that mixes two fluids in a T-microchannel. We carry out a numerical simulation to obtain the concentration gradient in the T-microchannel that correlates closely with the corresponding micro-schlieren image. By comparison, a relationship between the grayscale readouts of the micro-schlieren image and the concentration gradients presented in a microfluidic device is established. Using this relationship, we are able to analyze the mixing inhomogeneity from associate micro-schlieren image and demonstrate the capability of microscale schlieren technique with measurements in a microfluidic oscillator 4 . For optically transparent fluids, microscale schlieren technique is an attractive diagnostic tool to provide instantaneous full-field information that retains the three-dimensional features of the mixing process. Video LinkThe video component of this article can be found at

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“…The variation of salinity gradient with z is negligible at with the tested Reynolds numbers ( Re = 1 and 5). This is because diffusive mixing dominates mass transport for fluidic mixing in a T-microchannel under a Reynolds number of 140, despite the emergence of the Dean vortex [41]. Therefore, ∂ n /∂ y can be taken out of the integral in Equations (1) and (2), and a linear relation is expected between ∂ S /∂ y and I / I 0 :

\frac{I}{I_{0}} = C_{1} + C_{2} \frac{\partial S}{\partial y}

where C 1 and C 2 are constants.…”

Section: Calibration Processmentioning

confidence: 99%

Mapping the Salinity Gradient in a Microfluidic Device with Schlieren Imaging

Sun

Chen

Hsiao

2015

Sensors

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This work presents the use of the schlieren imaging to quantify the salinity gradients in a microfluidic device. By partially blocking the back focal plane of the objective lens, the schlieren microscope produces an image with patterns that correspond to spatial derivative of refractive index in the specimen. Since salinity variation leads to change in refractive index, the fluid mixing of an aqueous salt solution of a known concentration and water in a T-microchannel is used to establish the relation between salinity gradients and grayscale readouts. This relation is then employed to map the salinity gradients in the target microfluidic device from the grayscale readouts of the corresponding micro-schlieren image. For saline solution with salinity close to that of the seawater, the grayscale readouts vary linearly with the salinity gradient, and the regression line is independent of the flow condition and the salinity of the injected solution. It is shown that the schlieren technique is well suited to quantify the salinity gradients in microfluidic devices, for it provides a spatially resolved, non-invasive, full-field measurement.

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Theoretical and Experimental Investigations of Convective Micromixers and Microreactors for Chemical Reactions

Cited by 9 publications

References 12 publications

Rational design of the inlet configuration of flow systems for enhanced mixing

Rational design of the inlet configuration of flow systems for enhanced mixing

Analyzing Mixing Inhomogeneity in a Microfluidic Device by Microscale Schlieren Technique

Mapping the Salinity Gradient in a Microfluidic Device with Schlieren Imaging

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