The Reacting Flow, Diluted Species Interface governing equations are basically the same as for the Transport of Diluted Species and the Free and Porous Media Flow interfaces, the addition being the possibility to apply correction factors to calculate effective mass transport parameters in a porous domain.

In this section:

• Effective Mass Transport Parameters in Porous Media

Effective Mass Transport Parameters in Porous Media

The effective mass transport in a porous matrix is affected by the porosity of the porous media as the matrix of solid material lowers the available volume for transport. The tortuosity of the porous structure increases the transport length, and the species may interact with the pore walls. Effective transport parameters for the diffusivities (Deff) and mobilities (um,eff) are usually hard to measure. As an approximation, one can choose to use the parameter values for a non-porous domain (D, um) to calculate the corresponding effective values by multiplying with a correction factor feff:

A common way to calculate feff is to relate it to the porosity, with the following Bruggeman relation:

The settings for applying effective species transport parameter correction to a domain are found under the Porous Matrix Properties node.

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S i n g l e - P h a s e F l o w B r a n c h

There are several fluid flow interfaces available as listed in The CFD Module Physics Interfaces. This chapter describes the fluid flow groups under the

Single-Phase Flow branch () in the Model Wizard. The Mechanisms for Modeling Single-Phase Flow Interfaces helps to choose the best one to start with.

In this chapter:

•The Single-Phase Flow, Laminar Flow and Creeping Flow Interfaces

•The Single-Phase Flow, Turbulent Flow Interfaces

•The Single-Phase Flow, Rotating Machinery Interfaces

•Boundary Conditions for the Single-Phase Flow Interfaces

•Theory for the Single-Phase Flow Interfaces

•Theory for the Turbulent Flow Interfaces

•Theory for the Rotating Machinery Interfaces

•The Wall Distance Interface is also available and described in the COMSOL Multiphysics User’s Guide including the theory and how it relates to fluid flow.

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T h e M e c h a n i s m s f o r M o d e l i n g S i n g l e - P h a s e F l o w I n t e r f a c e s

The descriptions in this section are structured based on the order displayed in the Model Wizard and Fluid Flow branch. All the interfaces described in this section are found under the Fluid Flow>Single-Phase Flow branch () in the Model Wizard. Because most of the interfaces are integrated with each other, many features described cross reference to other interfaces. For example, features are usually available in both the laminar flow (Laminar Flow and Creeping Flow) and turbulent flow (Turbulent Flow, k- model, k- model, low-Re k- model, and Spalart-Allmaras) interfaces.

In this section:

•Selecting the Right Interface

•The Single-Phase Flow Interface Options

•Coupling to Other Physics Interfaces

•The Wall Distance Interface in the COMSOL Multiphysics User’s

Guide

See Also

Selecting the Right Interface

The Single-Phase Flow branch included with the CFD Module license has a number of subbranches with physics interfaces that describe different types of single-phase fluid flow. One or more of these physics interfaces can be added from the Model Wizard, either singularly or in combination with other physics interfaces for mass transport and heat transfer, for example.

Different types of flow require different equations to describe them. If the type of flow to model is already known, then select it directly from the Model Wizard. However, when you are uncertain of the flow type, or because it is difficult to reach a solution easily, you can start instead with a simplified model and add complexity as the model is built. Then test your way forward, comparing models and results. For single-phase flow, the Laminar Flow interface is a good place to start if this is the case.

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