Curved passive mixing structures: a robust design to obtain efficient mixing and mass transfer in microfluidic channels

Structured mini/micro-scale reactors continue to receive attention from both industry and academia due to their low pressure drop, high mass transfer rates and ease of scale-up when compared to conventional reactor technology. Commonly considered for heat and mass transfer limited reactions such as hydrogenations, hydrodesulphurization, oxidations and Fischer-Tropsch synthesis, the performance of these systems is highly dependent on mixing and the interfacial area between phases. While existing literature describes the initial flow patterns generated by a broad range of two-phase contactors, few studies explore the dynamic impacts of downstream passive mixing elements. Experimental and computational methodologies for characterizing two-phase flow pattern transitions, pressure drop, mixing and mass transfer are discussed, with relevant examples for serpentine and venturi-based passive mixing designs. The efficacy of these two configurations are explored in the context of pressure drop, conditions leading to significant interface renewal, and design considerations for optimizing mass transfer. Challenges associate with the characterization of multiphase flow through these systems are highlighted, and strategies suggested for both experimental and computational analysis of dynamic flow patterns and fluid-fluid interactions.

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Characterization of Mixing Performance Induced by Double Curved Passive Mixing Structures in Microfluidic Channels

Micromachines ◽

10.3390/mi12050556 ◽

2021 ◽

Vol 12 (5) ◽

pp. 556

Author(s):

Ingrid. H. Oevreeide ◽

Andreas Zoellner ◽

Bjørn. T. Stokke

Keyword(s):

Flow Direction ◽

Stationary Flow ◽

Channel Length ◽

Small Sample ◽

Confocal Imaging ◽

Microfluidic Channels ◽

High Performing ◽

Passive Micromixer ◽

Passive Mixing ◽

Parameter Values

Functionalized sensor surfaces combined with microfluidic channels are becoming increasingly important in realizing efficient biosensing devices applicable to small sample volumes. Relaxing the limitations imposed by laminar flow of the microfluidic channels by passive mixing structures to enhance analyte mass transfer to the sensing area will further improve the performance of these devices. In this paper, we characterize the flow performance in a group of microfluidic flow channels with novel double curved passive mixing structures (DCMS) fabricated in the ceiling. The experimental strategy includes confocal imaging to monitor the stationary flow patterns downstream from the inlet where a fluorophore is included in one of the inlets in a Y-channel microfluidic device. Analyses of the fluorescence pattern projected both along the channel and transverse to the flow direction monitored details in the developing homogenization. The mixing index (MI) as a function of the channel length was found to be well accounted for by a double-exponential equilibration process, where the different parameters of the DCMS were found to affect the extent and length of the initial mixing component. The range of MI for a 1 cm channel length for the DCMS was 0.75–0.98, which is a range of MI comparable to micromixers with herringbone structures. Overall, this indicates that the DCMS is a high performing passive micromixer, but the sensitivity to geometric parameter values calls for the selection of certain values for the most efficient mixing.

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Flow and mixing processes in a passive mixing microfluidic chip: Parameters’ estimation and colorimetric analysis

Тонкие химические технологии ◽

10.32362/2410-6593-2019-14-5-39-50 ◽

2019 ◽

Vol 14 (5) ◽

pp. 39-50

Author(s):

K. A. Sarbashev ◽

M. V. Nikiforova ◽

D. P. Shulga ◽

M. A. Shishkina ◽

S. A. Tarasov

Keyword(s):

Microfluidic Channel ◽

Measuring System ◽

Microfluidic Channels ◽

Colorimetric Analysis ◽

Microfluidic Systems ◽

Mixing Processes ◽

Information Measuring ◽

Flow Mixing ◽

Information Measuring System ◽

Passive Mixing

Objectives. The development of microfluidic systems is one of the promising areas of science and technology. In most procedures performed using microfluidic systems, effective mixing in microfluidic channels of microreactors (chips) is of particular importance, because it has an effect on the sensitivity and speed of analytical procedures. The aim of this study is to describe and evaluate the major parameters of the flow and mixing processes in a passive microfluidic micromixer, and to develop an information-measuring system to monitor the dynamics of flow (mixing) of liquids.Methods. This article provides an overview of the concept of microfluidic mixing chips (micromixers) and their classification, and analyzes the kinds of points of mixing and microfluidic channels for mixing. The article presents the description and calculations of the hydrodynamic similarity criteria (Reynolds, Dean and Peclet numbers), which are the critical parameters for creating and optimizing micromixers (for example, straight and curved channels in the flow rate range between 100 and 1000 µl/min). We have developed an information-measuring system to monitor the dynamics of flow (mixing) of liquids in a microfluidic channel, which consists of a microscope with a digital eyepiece (LOMO MIB, Russia), an Atlas syringe pump (Syrris Ltd., UK) and a passive mixing microfluidic chip of interest (made of clear glass). This system was designed to quickly illustrate the principles of mixing in microfluidic channels of different configurations.Results. The developed system has allowed carrying out a colorimetric analysis of the modes and dynamics of mixing two liquids (5% aqueous solution of azorubine dye and water) at the T-shaped mixing point, at the straight and curved (double-bend shaped) sections of the microfluidic channel of the passive-type micromixer with flow rates varying from 100 to 400 µl/min.Conclusions. According to the obtained calculations, the share of the advective mixing processes (formation of vortex flows and increase in the contact area of the mixed substances) in flowing liquids is significantly higher in curved microchannels. The developed information-measuring system to monitor the dynamics of flow (mixing) of liquids in a microfluidic channel is a convenient tool for optimizing the mixing modes in the channels of micromixers, and for designing new configurations of channels in microchips. It would allow intensifying processes and increasing the performance of microfluidic systems.

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Experimental and Computational Studies of Turbulent Mass Transfer in a Mixing Channel

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.1775 ◽

2008 ◽

Vol 6 (1) ◽

Author(s):

Lene K. Hjertager Osenbroch ◽

Bjorn H. Hjertager ◽

Tron Solberg

Keyword(s):

Mass Transfer ◽

Schmidt Number ◽

Turbulence Models ◽

Computational Studies ◽

Square Channel ◽

Numerical Predictions ◽

Turbulent Schmidt Number ◽

Passive Mixing ◽

Local Mean ◽

Presumed Pdf

Experiments are carried out for passive mixing in order to obtain local mean and turbulent velocities and concentrations. The mixing takes place in a square channel with two inlets separated by a block. A combined PIV/PLIF technique is used to obtain instantaneous velocity and concentration fields. Three different flow cases are studied. The 2D numerical predictions of the mixing channel show that none of the k - ? turbulence models tested is suitable for the flow cases studied here. The turbulent Schmidt number is reduced to obtain a better agreement between the measured and predicted mean and fluctuating concentrations. The multi-peak presumed PDF mixing model is tested and comparisons with experiments are encouraging.

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