Microfluidics Module
Perform Multiphysics Simulations of Microfluidic Devices with the Microfluidics Module
GeneralPurpose Microfluidics Simulations
The Microfluidics Module brings you easilyoperated tools for studying microfluidic devices. Important applications include simulations of labonachip devices, digital microfluidics, electrokinetic and magnetokinetic devices, and inkjets. The Microfluidics Module includes readytouse user interfaces and simulation tools, so called physics interfaces, for singlephase flow, porous media flow, twophase flow, and transport phenomena.
Scaling Down to Microscale Flows
Microfluidic flows occur on length scales that are orders of magnitude smaller than macroscopic flows. Manipulation of fluids at the microscale has a number of advantages – typically microfluidic systems are smaller, operate faster, and require less fluid than their macroscopic equivalents.
Energy inputs and outputs are also easier to control (for example, heat generated in a chemical reaction) because the surfacetoarea volume ratio of the system is much greater than that of a macroscopic system. In general, as the length scale of the fluid flow is reduced, properties that scale with the surface area of the system become comparatively more important than those that scale with the volume of the flow.
This is apparent in the fluid flow itself as the viscous forces, which are generated by shear over the isovelocity surfaces, dominate over the inertial forces. The Reynolds number (Re) that characterizes the ratio of these two forces is typically low, so the flow is usually laminar. In many cases, the creeping (Stokes) flow regime applies (Re«1). Laminar and creeping flows make mixing particularly difficult, so mass transport is often diffusion limited, but even in microfluidic systems diffusion is often a slow process. This has implications for chemical transport within microfluidic systems. The Microfluidics Module is designed specifically for handling momentum, heat, and mass transport with special considerations for fluid flow at the microscale.
Additional Images:
COMSOL’s generalpurpose multiphysics features are uniquely suited for handling the many microscale effects that are utilized in microfluidic devices. It is easy to set up coupled electrokinetic and magnetodynamic simulations – including electrophoresis, magnetophoresis, dielectrophoresis, electroosmosis, and electrowetting. In addition, chemical diffusion and reactions for dilute species functionality included in the module enable you to simulate processes occurring in labonachip devices. For simulating rarefied gas flows, you can use the specialized boundary conditions that activate flow simulation in the slip flow regime. The Microfluidics Module also provides dedicated methods for simulation of twophase flow with the level set, phase field, and moving mesh methods. For each of these, the capabilities of the Microfluidics Module include surface tension forces, capillary forces, and Marangoni effects.
Workflow for Modeling Microfluidic Devices
To model a microfluidic device, you begin by defining the geometry in the software by importing a CAD file or via the geometry modeling tools that are built into COMSOL Multiphysics. For importing geometry models, several choices are available to you: the CAD Import Module, for import of mechanical CAD models; the ECAD Import Module for import of electronic layouts; and the LiveLink™ products for CAD for a direct link to models created in a dedicated CAD software package. In the next step, you select appropriate fluid properties and choose a suitable physics interface. Initial conditions and boundary conditions are set up within the interface. Next, you define the mesh. In many cases, COMSOL’s automatically created default mesh, which is produced from physicsdependent defaults, will be appropriate for the problem. A solver is selected, again with defaults appropriate for the relevant physics, and the problem is solved. Finally, you can visualize the results.You access all of these steps from the COMSOL Desktop^{®}. The Microfluidics Module can solve for stationary and timedependent flows in 2D and 3D, and can be coupled with any other addon products for further extension of the modeling capabilities. One such example is for tracking particles released in the flow stream, which is made possible by combining with the Particle Tracing Module.
SinglePhase Flow
The Fluid Flow interfaces use physical quantities, such as pressure and flow rate, and physical properties, like viscosity and density, to define a fluidflow problem. The physics interface for laminar flow covers incompressible and weakly compressible flows. This Fluid Flow interface also allows for simulation of nonNewtonian fluid flow. A physics interface for creeping flow is used when the Reynolds number is significantly less than 1. This is often referred to as Stokes flow and is appropriate for use when viscous flow is dominant. It is usually applicable to microfluidic devices.
TwoPhase Flow
Three different methods are available for twophase flow: levelset, phasefield, and moving mesh methods. These are used to model two fluids separated by a fluid interface and where the moving interface is tracked in detail, including surface curvature and surface tension forces. The levelset and phasefield methods use a fixed background mesh and solve additional equations to track the interface location. The moving mesh method solves the flow equations on a moving mesh with boundary conditions to represent the fluid interface. In this case, additional equations are solved for the mesh deformation by means of the arbitrary LagrangianEulerian (ALE) method. All of these methods and their physics interfaces support both compressible and incompressible laminar flows, where one or both fluids can be nonNewtonian.
Rarefied Flow
Rarefied gas flow occurs when the mean free path of the molecules becomes comparable with the length scale of the flow. The Knudsen number, Kn, characterizes the importance of rarefaction effects on the flow. As the gas becomes rarefied (corresponding to increasing Knudsen number), the Knudsen layer, which is present within one mean free path of the wall, begins to have a significant effect on the flow. For Knudsen numbers below 0.01, rarefaction can be neglected and the laminar flow physics interfaces of the Microfluidics Module can be used with nonslip boundary conditions. For slightly rarefied gases (0.01<Kn<0.1), the Knudsen layer can be modeled by appropriate boundary conditions at the walls together with the continuum NavierStokes equations in the domain. In this instance, a special Slip Flow physics interface is available in the Microfluidics Module. To model higher Knudsen numbers, the Molecular Flow Module is required.
Porous Media Flow
Flow through porous media can also occur on microscale geometries. The flow is often frictiondominated when the pore size is in the micron range and Darcy’s law can be used. The Microfluidics Module features a dedicated physics interface for porous media flow based on Darcy's law. In this case, shear stresses perpendicular to the flow are neglected. For intermediate flows, a physics interface for the Brinkman equations is available. This physics interface models flow through a porous medium where shear stresses cannot be neglected. Both the StokesBrinkman formulation, suitable for very low flow velocities, and Forchheimer drag, which is used to account for effects at higher velocities, are supported. The fluid can be either incompressible or compressible, provided that the Mach number is less than 0.3.
A special physics interface for free and porous media models, both porous media using the Brinkman equations and laminar flow, automatically providing the coupling between the two. These interfaces are appropriate for microfluidic porous media flow. Example applications include paper microfluidics and transport in biological tissue.
Electrohydrodynamics Effects
At the microscale, a range of electrohydrodynamic effects can be exploited to influence the fluid flow. The Microfluidics Module is an excellent tool for modeling virtually any such effect. The electric field strength for a given applied voltage scales beneficially, making it easier to apply relatively large fields to the fluid with moderate voltages. In electroosmosis, the uncompensated ions in the charged electric double layer (EDL) present on the fluid surfaces are moved by an electric field, causing a net fluid flow. The Microfluidics Module provides a specialized electroosmotic velocity boundary condition as one of several fluid wall boundary conditions. Electrophoretic and dielectrophoretic forces on charged or polarized particles in the fluid can be used to induce particle motion, as can diamagnetic forces in the case of magnetophoresis. The Particle Tracing Module provides readytouse electrophoretic and dielectrophoretic particle forces. Combining the Microfluidics Module with the AC/DC Module enables you to model AC dielectrophoresis.
The manipulation of contact angles by the electrowetting phenomena is also easy in microscale devices. Electrowetting is a phenomenon that has been exploited as a basis for various new display technologies. The Microfluidics Module allows for direct manipulation of the contact angle with userdefined expressions including voltage parameters.
Mass Transport
The Microfluidics Module provides a dedicated physics interface for transport of diluted species. It is used to simulate chemical species transport through diffusion, convection (when coupled to fluid flow), and migration in electric fields for mixtures where one component – a solvent – is present in excess (90 mol% or greater). It is typically employed to model the performance of mixers. For modeling chemical reactions in microfluidic devices, you can combine the Microfluidics Module with the Chemical Reaction Engineering Module, which also makes available transport of concentrated species with binary diffusion.
Flexible and Robust Microfluidics Simulation Platform
For each of the Microfluidics interfaces, the underlying physical principles are expressed in the form of partial differential equations, together with corresponding initial and boundary conditions. COMSOL’s design emphasizes the physics by providing you with the equations solved by each feature and offering you full access to the underlying equation system. There is also tremendous flexibility to add userdefined equations and expressions to the system. For example, to model the transport of a species that significantly affects the viscosity of the fluid, simply type in concentrationdependent viscosity – no scripting or coding is required. When COMSOL compiles the equations, the complex couplings generated by these userdefined expressions are automatically included in the equation system. The equations are then solved using the finite element method and a range of industrialstrength solvers. Once a solution is obtained, a vast range of postprocessing tools are available to interrogate the data, and predefined plots are automatically generated to show the device response. COMSOL offers the flexibility to evaluate a wide range of physical quantities, including predefined quantities such as the pressure, velocity, shear rate, or the vorticity (available through easytouse menus), and arbitrary userdefined expressions
Interfacing with Excel^{®} and MATLAB^{®}
You can combine the Microfluidics Module with Microsoft^{®} Excel^{®} via LiveLink™ for Excel^{®}. This LiveLink™ product adds a COMSOL tab and specialized toolbar to the Excel ribbon for controlling the parameters, variables, and mesh, or for running a simulation. It also includes the capability to import and export Excel files for parameter and variable lists in the COMSOL Desktop^{®}.
If you wish to drive COMSOL simulations by means of script programming, you can use MATLAB^{®} and COMSOL together through the interface provided by the LiveLink™ for MATLAB^{®}. With this LiveLink™, you can access all the functionality of the COMSOL Desktop^{®} from a wealth of MATLAB commands. This provides a programmatic alternative to using the COMSOL Desktop^{®} for microfluidics simulations.
Product Features
 Anisotropic porous media flow
 Arbitrary userdefined expression for postprocessing
 Automatic boundary layer meshing
 Builtin variables for computing the Reynolds, Prandtl, Nusselt, Rayleigh, and Grashof numbers
 Creeping flow
 Capillary forces
 Electrokinetic effects
 Flow in porous media through Darcy's Law and the Brinkman Equations
 Fluidstructure interaction (FSI)^{1}
 Forchheimer drag for porous media flow
 Laminar flow
 Marangoni effects
 Migration effects
 Multiple species user interface
 Newtonian and nonNewtonian flow
 Particle tracing methods where particles can affect the flow (LagrangeEuler)^{2}
 Slip flow
 Shallow channel approximation for 2D flow
 Species transport in porous media
 Surface tension effects
 Twophase flow with the Levelset method
 Twophase flow with the phasefield method
 Twophase flow with the moving mesh method based on an arbitrary LagrangianEulerian (ALE) formulation
 Part Library with parametric geometry parts for channels in microfluidic components representing common configurations
^{1} Together with the Structural Mechanics Module or MEMS Module
^{2} Together with the Particle Tracing Module
Application Areas
 Capillary devices
 Chemical and biochemical sensors
 Dielectrophoresis (DEP)
 DNA chips
 Electrocoalescence
 Electrokinetic flow
 Electroosmosis
 Electroosmosis
 Electrowetting
 Emulsions
 Inkjets
 Labonachip
 Magnetophoresis
 Microreactors, micropumps, and micromixers
 Microfluidic sensors
 Slightly rarefied gas flow (slip flow)
 Static mixers
 Surface tension effects
 Twophase flow
 Polymer flow and viscoelastic flow
 Optofluidics
Inkjet Nozzle — Level Set Method
Although initially invented to be used in printers, inkjets have been adopted for other application areas, such as within the life sciences and microelectronics. Simulations can be useful to improve the understanding of the fluid flow and to predict the optimal design of an inkjet for a specific application. The purpose of this application is to ...
Capillary Filling
This example studies a narrow vertical cylinder placed on top of a reservoir filled with water. Because of wall adhesion and surface tension at the air/water interface, water rises through the channel. Surface tension and wall adhesive forces are often used to transport fluid through microchannels in MEMS devices or to measure, transport and ...
Drug Delivery System
This example describes the operation of a drug delivery system that supplies a variable concentration of a water soluble drug. A droplet with a fixed volume of water travels down a capillary tube at a constant velocity. Part of the capillary wall consists of a permeable membrane separating the interior of the capillary from a concentrated ...
Controlled Diffusion Separator
This model simulates an Hshaped microcell designed for diffusioncontrolled separation. The cell puts two different laminar streams in contact for a controlled period of time. The contact surface is welldefined and, by controlling the flow rate, it is possible to control the amount of species that are transported from one stream to the other ...
Electroosmotic Micromixer
Microlaboratories for biochemical applications often require rapid mixing of different fluid streams. At the microscale, flow is usually highly ordered laminar flow, and the lack of turbulence makes diffusion the primary mechanism for mixing. While diffusional mixing of small molecules (and therefore of rapidly diffusing species) can occur in a ...
Lamella Mixer
At the macroscopic level, systems usually mix fluids using mechanical actuators or turbulent 3D flow. At the microscale level, however, neither of these approaches is practical or even possible. This model demonstrates the mixing of fluids using laminarlayered flow in a MEMS mixer. This model analyzes the steadystate condition of the fluid ...
Droplet Breakup in a TJunction
Emulsions consist of small liquid droplets immersed in an immiscible liquid and widely occur in the production of food, cosmetics, fine chemicals, and pharmaceutical products. The quality of the product is typically dependent on the size of the droplets. Simulating these processes can help in optimizing these droplets as well as other process ...
Transport in an Electrokinetic Valve
This application presents an example of pressure driven flow and electrophoresis in a 3D micro channel system. Researchers often use a device similar to the one in this model as an electrokinetic sample injector in biochips to obtain welldefined sample volumes of dissociated acids and salts and to transport these volumes. Focusing is obtained ...
Electrowetting Lens
The contact angle of a twofluid interface with a solid surface is determined by the balance of the forces at the contact point. In electrowetting the balance of forces at the contact point is modified by the application of a voltage between a conducting fluid and the solid surface. In many applications the solid surface consists of a thin ...
Every business and every simulation need is different.
In order to fully evaluate whether or not the COMSOL Multiphysics^{®} software will meet your requirements, you need to contact us. By talking to one of our sales representatives, you will get personalized recommendations and fully documented examples to help you get the most out of your evaluation and guide you to choose the best license option to suit your needs.
Just click on the "Contact COMSOL" button, fill in your contact details and any specific comments or questions, and submit. You will receive a response from a sales representative within one business day.
Next Step
Request a Software Demonstration
Platform Product
 COMSOL Multiphysics^{®}
Deployment Products
 COMSOL Compiler™
 COMSOL Server™
Electromagnetics
Modules AC/DC
 RF
 Wave Optics
 Ray Optics
 Plasma
 Semiconductor
Structural Mechanics & Acoustics Modules
 Structural Mechanics
 Multibody Dynamics
 MEMS
 Acoustics
Fluid Flow &
Heat Transfer Modules CFD
 Polymer Flow
 Microfluidics
 Porous Media Flow
 Subsurface Flow
 Pipe Flow
 Molecular Flow
 Metal Processing
 Heat Transfer
Chemical Engineering
Modules Chemical Reaction Engineering
 Battery Design
 Fuel Cell & Electrolyzer
 Electrodeposition
 Corrosion
 Electrochemistry

Multipurpose Products
 Optimization Module
 Uncertainty Quantification Module
 Material Library
 Particle Tracing Module
 Liquid & Gas Properties Module
Interfacing Products
 LiveLink™ for MATLAB^{®}
 LiveLink™ for Simulink^{®}
 LiveLink™ for Excel^{®}
 CAD Import Module
 Design Module
 ECAD Import Module
 LiveLink™ for SOLIDWORKS^{®}
 LiveLink™ for Inventor^{®}
 LiveLink™ for AutoCAD^{®}
 LiveLink™ for Revit^{®}
 LiveLink™ for PTC^{®} Creo^{®} Parametric™
 LiveLink™ for PTC^{®} Pro/ENGINEER^{®}
 LiveLink™ for Solid Edge^{®}
 File Import for CATIA^{®} V5

Multipurpose Products
 Optimization Module
 Uncertainty Quantification Module
 Material Library
 Particle Tracing Module
 Liquid & Gas Properties Module
Interfacing Products
 LiveLink™ for MATLAB^{®}
 LiveLink™ for Simulink^{®}
 LiveLink™ for Excel^{®}
 CAD Import Module
 Design Module
 ECAD Import Module
 LiveLink™ for SOLIDWORKS^{®}
 LiveLink™ for Inventor^{®}
 LiveLink™ for AutoCAD^{®}
 LiveLink™ for Revit^{®}
 LiveLink™ for PTC^{®} Creo^{®} Parametric™
 LiveLink™ for PTC^{®} Pro/ENGINEER^{®}
 LiveLink™ for Solid Edge^{®}
 File Import for CATIA^{®} V5