Fluidic Mixing

Veryst has deep expertise in fluidic mixing processes, which we leverage for our clients across industries.  A fundamental aspect of mixing is the stretching and folding of the interface between initially separated substances.  This occurs in many forms and systems: agitated versus static mixers, laminar versus turbulent flows, lab versus production scale, etc.  It also occurs in systems where mixing is weakly coupled with the flow (passive mixing) or tightly coupled with the flow (mixing of variable density substances, flows with chemical reactions, multiple phases, etc.).

Veryst’s consultants employ advanced computational fluid dynamics (CFD) tools and analytical models to understand and visualize complex flow behavior.  We use our grounded knowledge of computational methods, fluid mechanics, and physics to provide practical design recommendations.  Clients use our analyses to understand and improve mixing performance and to scale-up or down between lab, pilot and production scale systems.

Microfluidic and Laminar Mixing

Microfluidic mixer based on a serpentine channel that generates recirculation to promote fluid mixing
Microfluidic mixer based on a serpentine channel
that generates recirculation to promote fluid mixing.

Mixing input streams is a key step in microfluidic and laminar flow systems such as flow cells in DNA sequencing, small-batch mRNA vaccine production, and lateral flow, wearable, or point-of-care diagnostic tests.

A key design challenge of microfluidic and laminar fluidic systems is how to mix reagents rapidly, effectively, and efficiently.  Unfortunately, the efficient turbulent mixing available to larger scale flows is generally not available for microfluidic and laminar systems.  Moreover, even though microfluidic devices have channels with small dimensions, the diffusive mixing occurring within is still generally far too slow and inefficient.  Additional challenges for these systems include efficient use of reagents and developing designs that can be manufactured repeatably, reliably, and cost-effectively.

Effective and efficient mixing in microfluidic and laminar systems may be accomplished passively via geometrical features such as serpentine channels (see figure) or active methods such as asymmetric wall motion or agitation.  We explore and compare passive chaotic mixing via serpentines, rings, and herringbone grooves in an instructive case study.


Turbulent Mixing

Turbulent mixing systems leverage the eddies and fluctuations that arise from the chaotic nature of such flows to stretch and fold the interfacial areas between the substances being mixed.  In a typical mixer, large eddies are created either by mechanical agitation or shear (e.g., a jet into a quiescent medium).  These eddies disperse and break into smaller and smaller flow scales.  This process stretches, folds, and engulfs pockets of unmixed fluid to create more interfacial surface area and to promote diffusion.  Mixing in turbulent flows is typically characterized by the Reynolds, Schmidt, and Damköhler numbers, which quantify the importance of inertial forces, momentum diffusion, and chemical time scales, respectively.

An example of turbulent mixing is shown in the animation below of flash nanoprecipitation (FNP) in a continuous multi-inlet vortex mixer.  FNP is an efficient approach for high volume manufacturing of nanoparticles, such as the lipid nanoparticles found in mRNA vaccines, that relies on the rapid mixing of streams containing the nanoparticle components.  Veryst was able to predict micromixing rates in a multi-inlet vortex mixer for lipid nanoparticle production using high-fidelity computational fluid dynamics (CFD).  Simulations such as these can help predict the minimum flow rate required to produce the desired nanoparticle size distributions while avoiding potentially damaging flow shear stresses.

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Active Mixing in a Microwell by Repetitive Pipetting

A simple way of mixing small volumes (microliters or milliliters) of reagents is by repeatedly dispensing and withdrawing solution from a microwell or tube. In this case study, we used a two-phase multiphysics simulation with coupled fluid flow and mass transfer to analyze the efficacy of this active mixing process.

Chaotic Mixing in Microfluidic Devices

Fast mixing of reagents in microfluidic channels and devices is important for DNA sequencing, mRNA vaccine production in small-batch pharmaceutical processes, and point-of-care diagnostics. In this case study, Veryst used computational fluid dynamics simulations to evaluate the mixing performance of three commonly used microfluidic mixers.

Chemical Carryover in Microfluidic Devices

Removing reagents or sample from a previous processing step via a wash cycle is a common challenge in microfluidic assays used in diagnostic, genomic, biomedical, pharmaceutical and other applications. This case study shows how finite element simulations may be used to predict and optimize wash cycle performance.

Concentration Gradients in Microfluidic Devices

Controlling spatial variations in chemical concentration is important for designing and operating many microfluidic devices across a wide range of industries and applications including diagnostics, genomics, and pharmaceutics. In this case study, we show how simulations may be used to quantify and control concentration gradients in microfluidic devices.

Laminar Static Mixer Analysis

Laminar static mixers are often employed in industrial environments when the mixing of two or more fluids is required. However, their performance is impossible to analyze with a pure CFD approach. Veryst, in collaboration with Nordson EFD, developed a unique computational modeling tool to evaluate and optimize the design of such mixers.

Micromixing in a Multi-Inlet Vortex Mixer

Flash nanoprecipitation (FNP) is a novel method to produce nanoparticles for a variety of applications, including mRNA vaccine manufacturing. This case study demonstrates the high-fidelity prediction of micromixing rates, which are critical to controlling the size distribution of nanoparticles created using FNP.

Oxygen Transport and Cellular Uptake in a Microchannel

Oxygen transport is a key factor in the design of cell culture systems such as organs-on-a-chip, microphysiological systems, and bioreactors. In this case study, we use multiphysics simulation to analyze oxygen transport and cellular uptake in a model microchannel bioreactor.

Scaling Yield and Mixing in Chemical Reactors

Scaling chemical reactions from the lab to pilot or production requires a detailed understanding of the physical system, which frequently involves heat transfer, mass transfer, reaction kinetics, and fluid flow. This case study illustrates how multiphysics simulations can support design decisions involved in scaling up chemical reactors.

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