COMSOL 6.3 - Particle Properties

Particle Properties

Use the node to specify the particle size, density, charge number, and particle velocity based on whether a Newtonian formulation or massless formulation is selected.

Particle Properties

This section is shown for the following choices in the physics interface list:

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, and

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Using Material Data

Usually it is necessary to specify the particle density. Depending on what additional forces or other physics features are added to the model, you might need to provide additional material properties, such as specific heat (if you selected the checkbox). You may either type values or expressions for these particle material properties directly, or take them from a node, which could either be a user-defined or a material from one of the Material Libraries.

The default value in the list is . If you wish to use data from a or from the , first add the material to the model (right-click either under the model component or under ) and then select it from the list.

Choosing Which Particle Size Parameters to Specify

If is selected from the list in the physics interface section, select an option from the list:

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(the default),

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, or

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Then enter the applicable values or expressions for the following:

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ρp (SI unit: kg/m3). By default this is taken . If is selected, the default value is 2200 kg/m3.

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dp (SI unit: m). The default is 1 μm.

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mp (SI unit kg). The default is 1 mg.

If or is selected from the list, just enter a value or expression for the . Then the initial particle mass or diameter is controlled by the release features.

Select an option from the list: (the default) or . If is selected, enter a value or expression for the σp (SI unit: N/m). The default is 0.0729 N/m.


	Liquid droplets/bubbles must be selected for at least one species in the model in order to use the Droplet Breakup and Nozzle features.

Charge Number

Enter a value or expression for the Z (dimensionless). The default is 0. The particle charge is the product of the charge number with the elementary charge e.

Particle Velocity

This section is shown when is selected as the for the physics interface. Enter a vector for the v (SI unit: m/s) based on space dimension. The formulation means that the particles follow streamlines of the particle velocity expression.

Thermal Properties

This section is shown when the following conditions are satisfied:

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the checkbox is selected in the physics interface section, and

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Either or is selected from the list in the physics interface section.

Enter a value or expression for the hp (SI unit: J/kg). The default value is 42,000 J/kg.

Accretion Rate

This section is shown when or is selected from the list in the physics interface section. The accretion rate is the rate of increase or decrease in particle mass after the particles have been released; it can be used to model phenomena such as accretion, evaporation, condensation, and sublimation on the model particles.

Specifically, if the particles represent liquid droplets that can evaporate in a surrounding gas, add a Droplet Evaporation node to the model and then select it from the list. Otherwise, keep the default value, , and enter a value or expression for the R (SI unit: kg/s) directly. The default is 0. If the is positive, particles will grow continuously over time after they are released.

Additional Material Properties

This section contains inputs for any other particle material properties that might be required. The settings displayed in this section depend on the type of forces and other physics features that are included in the model. For simpler models, this section is often empty.

The additional particle material properties, and the physics features that require them, are shown in Table 5-1. Note that it is possible to set up a model with multiple different particle species, by having two or more instances of the node. If some of the forces in this list are only applied to a single particle species, then the corresponding material properties will only be shown in the node for that species.

Table 5-1: Additional Particle Material Properties.
Properties	Activation Conditions
Dynamic viscosity	Used by the Hadamard-Rybczynski drag law; certain Acoustophoretic Radiation Force settings; some droplet breakup models; and some options for the Nozzle release feature.
Bulk viscosity	Sometimes required by the Acoustophoretic Radiation Force.
Relative permittivity	Required to model accumulation of charge on the particle surfaces, for certain charging models. Always required by the Dielectrophoretic Force.
Relative permeability	Always required by the Magnetophoretic Force.
Electric conductivity	Always required by the Dielectrophoretic Force.
Specific heat capacity	Always required if the particle temperature is solved for. Sometimes required by the Acoustophoretic Radiation Force even if particle temperature is not solved for.
Coefficient of thermal expansion	Sometimes required by the Acoustophoretic Radiation Force.
Ratio of specific heats	Sometimes required by the Acoustophoretic Radiation Force.
Thermal conductivity	Sometimes required by the Acoustophoretic Radiation Force. Always required by the Thermophoretic Force. Note that all heat sources and sinks on particles (such as Convective Heat Losses) use a small Biot number approximation that assumes infinite particle conductivity.
Speed of sound	Sometimes required by the Acoustophoretic Radiation Force.


	When solving for particle temperature (by selecting the Compute particle temperature checkbox in the physics interface Additional Variables section), if the particle material has a temperature-dependent density, select Specify particle mass and density from the Particle property specification list, so that the particle mass (rather than particle diameter) is conserved, even as the particle density changes over time.


	The Particle Properties node is a default feature for all particle tracing physics interfaces. This default node cannot be deleted or disabled, and it is not possible to paste or duplicate this node in the model builder. However it is possible to add more than one instance of this Particle Properties node to the same model. When you do so, each instance corresponds to a different species of particle. For example, two Particle Properties nodes could represent ions and electrons, or white blood cells and bacteria. Unlike the default Particle Properties node, these nondefault nodes can be deleted, disabled, duplicated or pasted in the model builder. When two or more species are in the same model, you can decide which species is released by each particle release feature, such as the Release, Inlet, or Release from Grid feature. To do so, select the appropriate Particle Properties node from the Released particle properties list in the physics feature Released Particle Properties section. For more information, see Particle Tracing with Multiple Species in the Particle Tracing Modeling chapter.