How can I simulate mixing two different fluids with COMSOL Multiphysics software?

To simulate mixing two different fluids with COMSOL Multiphysics software, you can follow these general steps:

Set up a 3D geometry of the mixing device or chamber using the built-in geometry tools or import a CAD file.

Define the properties of the two fluids, including density, viscosity, and initial concentrations of any species of interest.

Set up the fluid flow model using the Navier-Stokes equations, selecting appropriate boundary conditions and solver settings.

Set up the transport model for any species of interest using the advection-diffusion equation, specifying initial and boundary conditions.

Couple the fluid flow and transport models using the built-in multiphysics couplings.

Define the appropriate physics and simulation parameters, such as the inlet flow rates, mixing time, and mesh size.

Run the simulation and analyze the results, such as the concentration profiles and mixing efficiency.

Here is an example of simulating mixing two fluids using COMSOL Multiphysics:

Consider a simple T-shaped mixing channel as shown below, where a blue fluid and a red fluid are introduced from the two inlets and mixed in the channel:

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To simulate this system using COMSOL Multiphysics software, you can follow these steps:

Create the geometry of the mixing channel using the built-in geometry tools or import a CAD file.

Define the properties of the two fluids, such as their densities and viscosities.

Set up the fluid flow model using the Navier-Stokes equations, specifying the inlet flow rates, velocities, and boundary conditions.

Set up the transport model for the two fluids using the advection-diffusion equation, specifying the initial concentrations and boundary conditions.

Couple the fluid flow and transport models using the built-in multiphysics couplings.

Define the simulation parameters, such as the time step, number of iterations, and mesh size.

Run the simulation and analyze the results, such as the concentration profiles and mixing efficiency.

With COMSOL Multiphysics software, you can also simulate more complex mixing scenarios, such as turbulent mixing, reactive mixing, and multiphase mixing.

Alessio Pricci

Our research group has modeled the same problem for a Y-micromixer (2 inlet/ 2fluids, 1 outlet and single domain) in:

https://www.researchgate.net/publication/354032403_Exploiting_limitations_of_fused_deposition_modeling_to_enhance_mixing_in_3D_printed_microfluidic_devices

DOI: 10.1108/RPJ-03-2021-0051

Here the same physics have been introduced (Laminal flow and TDS).

The key to model the two fluids is to use the "inlet concentration" settings in TDS; when you define the inlet in TDS (as you do in laminar flow) you specify molar concentration.

I suggest you to choose c=0 for fluid A and c=1 for fluid B, that is a normalized concentration (more meaningful, especially for publication).

As initial concentration state in TDS, you can set c=0; in fact, at the beginning (time = 0) you have no concentration in your mixing channel.

If simulation is steady-state the same applies.

Best regards,

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