•Model Builder Options for Physics Feature Node Settings Windows

•Theory for the Mixture Model Interface

•Slip Velocity Models

•The Mixture Model, Laminar Flow Interface

•Mixture Properties

•Mass Transfer

•Volume Force

•Gravity

• Initial Values

See Also

•Boundary Conditions for the Mixture Model Interfaces In the COMSOL Multiphysics User’s Guide:

•Working with Geometry

•Show Stabilization

In the COMSOL Multiphysics Reference Guide:

•Stabilization Techniques

•Numerical Stabilization

Mixture Properties

The Mixture Properties feature contains the material properties for the continuous phase and the dispersed phase. It also contains settings for the viscosity model.

D O M A I N S E L E C T I O N

From the Selection list, choose the domains to use the mixture properties.

M A T E R I A L S

Select the fluid materials to use for the material properties. The default material used for both Continuous phase and Dispersed phase is the Domain material, which uses the material defined for the domain. Select another material (when available).

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C O N T I N U O U S P H A S E P R O P E R T I E S

The default Density, continuous phase c (SI unit: kg/m3) uses values From material (as selected in the Materials section). If User defined is selected, enter another value or expression.

The default Dynamic viscosity, continuous phase c (SI unit: Pa·s), uses values From material. It describes the relationship between the shear stresses in a fluid and the shear rate. Intuitively, water and air have a low viscosity, and substances often described as thick, such as oil, have a higher viscosity. If User defined is selected, enter another value or expression.

D I S P E R S E D P H A S E P R O P E R T I E S

The default Density, dispersed phase d (SI unit: kg/m3) uses values From material (as selected in the Materials section). If User defined is selected, enter another value or expression.

Enter the Diameter of particles/droplets dd (SI unit: m). The default is 10 3 m (1 mm).

If Liquid droplets/bubbles is selected from the Dispersed phase list on The Mixture Model, Laminar Flow Interface or The Mixture Model, Turbulent Flow Interface Settings window, then the next option is

Note

available.

The default Dynamic viscosity, dispersed phase d (SI unit: Pa·s), uses values From material. (as selected in the Materials section). If User defined is selected, enter another value or expression.

M I X T U R E M O D E L

The options available from Mixture viscosity model list are based on the selection made on The Mixture Model, Laminar Flow Interface and The

Mixture Model, Turbulent Flow Interface Settings window from the

Note

Dispersed phase list (Solid particles or Liquid droplets/bubbles).

Select the Mixture viscosity model—Krieger type, User defined, or Volume averaged. When Solid particles is selected as noted above only Krieger type and User defined are available. When Liquid droplets/bubbles is selected, Volume averaged is also available.

User Defined

If User defined is selected, enter a value or expression for the Viscosity (SI unit: Pa s).

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Krieger Type

Select Krieger type to model the most generally valid expression for the mixture

viscosity:

	=		1		d		–2,5 max
				– -----------
		c		max

where max is the maximum packing concentration, which for solid particles is approximately 0.62. The dimensionless parameter * 1 for solid particles and

+ 0,4

= ----d----------------------c

d + c

for drops and bubbles.

When Krieger type is selected, enter a value or expression for the Maximum packing concentration max (unitless). The default is 0.62

Volume Averaged

Select Volume averaged to model the mixture viscosity of liquid-liquid mixtures, which uses the following equation for the viscosity:

= d d + c c

The mixture model interfaces always uses the mixture viscosity in the particle Reynolds number expression used to calculate the slip velocity, thereby accounting for the increase in viscous drag due to particle-particle interactions.

D I S T A N C E E Q U A T I O N

	This section is available in a turbulent flow interface that includes The
	Wall Distance Interface (as described in the COMSOL Multiphysics
Note	User’s Guide).

Specify how the reference length scale is defined:

•The default setting is Automatic, in which case the wall distance is automatically evaluated as:

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