Design and Numerical Simulation of a Microfluidic Mixer Using COMSOL Multiphysics

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 mixingindex or pressure-drop value that has not been verified is stated in this draft.