Design and Numerical Simulation of a Microfluidic Mixer Using COMSOL Multiphysics

Abstract

Microfluidic devices are used for the handling of small volumes of fluid by means of microscale channels and are generally regarded as suitable for chemical analysis, biomedical testing, pharmaceutical processing, and for use in lab-on-a-chip systems. It is difficult to achieve efficient mixing when the Reynolds number is low since the flow is usually laminar and turbulent eddies are either weak or missing. The present paper describes a numerical-study framework which is used for the design and simulation of a passive microfluidic mixer with the help of COMSOL Multiphysics. The method employed involves a three-dimensional channel geometry, laminar-flow modelling, and the modelling of species transport in order to assess the velocity, pressure, concentration distribution, and the quality of mixing at the outlet. A mixing index based on concentration variance is introduced in order to allow a quantitative comparison between different design cases. The paper also establishes a repeatable procedure for carrying out mesh-independence checks and for conducting parametric studies on inlet velocity, channel dimensions, and the geometry of the mixing element. The reference study by Jomha, Oruç, and Yayla, which used ANSYS Fluent to investigate an optimised zigzag split-and-recombination micromixer, is included here solely as a benchmark in the existing literature and is not presented as a result from the current COMSOL model. The numerical values from the user\'s model have to be entered after the COMSOL solution and the derived quantities have been verified. For this reason, no mixing-index or pressure-drop value that has not been verified is stated in this draft

Introduction

The text discusses the design and numerical analysis of a passive microfluidic mixer using COMSOL Multiphysics. Microfluidics involves controlling small amounts of fluid through tiny channels and is widely used in medical diagnostics, biochemical analysis, drug development, and chemical processing. One major challenge is mixing fluids efficiently because flow at microscale dimensions is generally laminar, making molecular diffusion the primary mixing mechanism.

The project proposes a passive micromixer that uses a wavy microchannel and circular chambers to improve mixing without requiring external energy. The design aims to enhance fluid mixing while maintaining a reasonable pressure drop.

The methodology involves creating or importing a three-dimensional CAD geometry, defining fluid properties and boundary conditions, and simulating laminar flow and species transport using COMSOL. The governing equations include the continuity equation, Navier–Stokes momentum equation, and convection–diffusion equation. Two inlets introduce fluids at a velocity of 0.001 m/s, while the outlet is maintained at a reference pressure of 0 Pa.

Mixing performance is evaluated using the mixing index, calculated from the concentration variation at the outlet. A higher mixing index indicates more uniform mixing. Pressure drop, velocity distribution, and concentration patterns are also examined. Mesh independence and solver convergence must be verified using coarse, medium, and fine meshes to ensure reliable results.

The project builds on previous research involving split-and-recombination micromixers and identifies the need for a consistent COMSOL simulation procedure, quantitative performance measurements, and comparison with existing ANSYS-based results under equivalent conditions.

Conclusion

The numerical approach to analyzing a passive microfluidic mixer based on CAD and COMSOL Multiphysics is introduced in this manuscript. The methodology employs both laminar flow equations and species transport equations with boundary conditions explicitly stated. Mesh independence test and outlet concentration variance mixing criteria are also incorporated into the methodology. Previous literature suggests that splitting and recombining and zigzag designs improve interfacial stretching; however, both designs need to be evaluated with respect to pressure drop as well. Conclusions regarding this particular design will be drawn only after the actual COMSOL outputs have been obtained. Further work may include a mesh independent parametric analysis, geometry comparisons, optimization of inlet velocity and dimensions of mixing element, experimental work with dyes/concentrations, and fabrication feasibility.

References

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Copyright

Copyright © 2026 Pratham Utkarsh Vajanam, Sagar Shantkumar Koshti, Mahesh Dashrath Survase, Vishal Syamgir Giri, V. L. Jagtap. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.