Phase Properties

The node has the material properties settings for the pure continuous and dispersed phases. It also has settings for the viscosity models for each of the two interpenetrating phases and the drag model. When the dispersed phase consists of solid particles, it also has settings for the solid pressure model.

Model Inputs

Fluid properties, such as density and viscosity, can be defined through user inputs, variables, or by selecting a material. For the latter option, additional inputs, for example temperature or pressure, may be required to define these properties.

Temperature

By default, the model input is set to , and the temperature is controlled from Default Model Inputs under or by a locally defined Model Input. If a Heat Transfer interface is included in the component, it controls the temperature . Alternatively, the temperature field can be selected from another physics interface. All physics interfaces have their own tags (). For example, if a Heat Transfer in Fluids interface is included in the component, the option is available for T.

You can also select from the model input in order to manually prescribe T.

Absolute Pressure

This input appears when a material requires the absolute pressure as a model input. The absolute pressure is used to evaluate material properties, but it also relates to the value of the calculated pressure field. There are generally two ways to calculate the pressure when describing fluid flow: either to solve for the absolute pressure or for a pressure (often denoted gauge pressure) that relates to the absolute pressure through a reference pressure.

The default pA is p+pref, where p is the dependent pressure variable from the Navier-Stokes or RANS equations, and pref is from the user input defined at the physics interface level. When pref is nonzero, the physics interface solves for a gauge pressure. If the pressure field instead is an absolute pressure field, pref should be set to 0.

The field can be edited by clicking (

) and entering the desired value in the input field.


	Model Inputs and Multiphysics Couplings in the COMSOL Multiphysics Reference Manual

Materials

Select the materials to use for the material properties of the continuous phase and the dispersed phase respectively (when they are defined to take their values ). By default, the default material used for the is the . This corresponds to the material currently applied to the domain in question. The uses per default. A valid material must be selected instead.

Other materials present can be selected from the or list in order to use that material’s properties for the liquid or gas, respectively.

Continuous Phase Properties

Density, Continuous Phase

The default ρc (SI unit: kg/m3) uses values . For enter another value or expression.

Dynamic Viscosity, Pure Continuous Phase

The dynamic viscosity describes the relationship between the shear stresses and the shear rate in a fluid. Intuitively, water and air have a low viscosity, and substances often described as thick, such as oil, have a higher viscosity. The dynamic viscosity of the pure continuous phase refers to the viscosity the fluid would have in the absence of the dispersed phase.

The default μc (SI unit: Pa·s) uses values . The value of the viscosity is then the value defined for the material selected in the section for the continuous phase. For define a different value or expression.

Dispersed Phase Properties

The default ρd (SI unit: kg/m3) uses values . For enter another value or expression.

Enter a value or expression for the dd (SI unit: m). The default is 10−3 m (1 mm).


	The Dynamic viscosity, pure dispersed phase μd (SI unit: Pa·s) field is available when Liquid droplets/bubbles is selected as the Dispersed phase in The Euler-Euler Model Interfaces. The default uses values From material. The value of the viscosity is then the value defined for the material selected in the Materials section for the dispersed phase. For User defined define a different value or expression.

Viscosity Model

Select a model for the — (the default), (available for liquid droplets and bubbles) or . Krieger type is appropriate for dispersed phases that do not form any pure phase regions. Volume average is more appropriate when the dispersed phase effectively can become the only phase in some regions.

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For , select an option for The default is to use

= 1.0 for droplets and bubbles and

= 0.62 for particles. Select to enter another value or expression for

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For enter a value or expression for the . The default expression corresponds to the Krieger type viscosity with maximum packing equal to 0.62.

Select a — (default), or . The option is appropriate when the maximum packing is controlled by the mixture viscosity. The option is more appropriate if the maximum packing is controlled in some other way, for example by solid pressure. Select to enter an expression for the .

Select a — (default), (available for bubbles and droplets), (available for solid particles) or . The model prescribes

which basically prescribes a small value for

and should be combined with a solid pressure model.

Drag Model

The models are described in The Euler–Euler Model Equations. When the dispersed phase corresponds to , the , , ,and models are available. For , the , , models are available. Select the option to specify an expression for the drag coefficient CD.

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The is valid for dispersed, rigid spheres and can be used for particle Reynolds numbers less than approximately 2.5·105. The Schiller-Naumann model is a general purpose model for diluted flows.

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The is appropriate for diluted flows at low Reynolds numbers.

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The model can for solid particles be regarded as a generalization of the Schiller-Naumann model in that it can be used also for dense flows. For droplets and bubbles, the Ishii-Zuber model also takes deformation of the fluid particles into account. The deformation depends on the , σ. Use a predefined expression, select or . Then select an option from the list that displays below (for example, , and so forth). For enter a value or expression for the surface tension coefficient σ (SI unit: N/m).

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The model describes the drag force coefficient for dispersed phase flows for all concentrations of the dispersed solid, including high concentrations.

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The model describes non-spherical particles for low and moderate particle Reynolds numbers. Enter a value between 0 and 1 for the Sp (dimensionless).

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The model describes the drag for diluted droplets and bubbles for any particle Reynolds number. The correlation is available in three versions, , and . The Tomiyama et al. model depends on the , σ that is selected in the same way as for the Ishii-Zuber model.

Solid Pressure Model

The solid pressure models the particle dispersion due to collisions and friction between the solid particles. Details of the implemented models are described in Solid Pressure.

This section is available when is selected as the in The Euler-Euler Model Interfaces. Select a ∇ps.

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The (the default) disables solid pressure and leaves the collision to be described by a mixture viscosity. This option is appropriate for solid suspension, typically solids suspended in liquids.

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The other options, , , and describes particle-particle interaction for dispersed solids, typically solid particles in gas flows. These options should be combined with the Gidaspow model or a small user defined value for

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For enter an expression for the , G (SI unit: N/m2).

Mixing length limit

When the lmix, lim is set to , the mixing length limit is evaluated as the shortest side of the geometry bounding box. If the geometry is, for example, a complicated system of slim entities, this measure can be too high. In such cases, it is recommended that the mixing length limit is defined manually. Select to enter a different value or expression.