Particle Tracing with Multiple Species
It is possible to solve for the trajectories of several different types of particle as part of the same analysis. For example:
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Use The Mathematical Particle Tracing Interface to model gravitational attraction between stars or planets of different sizes.
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Use The Charged Particle Tracing Interface to model the reactions between ions, electrons, and neutral atoms or molecules in a low-pressure environment. You can also model the Coulomb force between electrons and different species of ion.
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Use The Particle Tracing for Fluid Flow Interface to model separation of different types of biological cell. You can also model the filtration of sediment particles with different masses; the masses can have a number of discrete values or be sampled from a continuous distribution, such as a normal distribution.
You can define additional species in the model by adding more instances of the Particle Properties feature. One Particle Properties node is always present in the interface by default, and cannot be deleted. When you create additional Particle Properties nodes, they are always listed directly under the default Particle Properties node in the Model Builder.
If multiple types of particle are present in the same model, you can choose which species to release with every particle release feature, such as the Inlet, Release from Grid, and Secondary Emission features. Expand the Released Particle Properties section, which includes a list of all of the available Particle Properties nodes. Then select the node corresponding to the species that the feature should release.
Figure 2-4: The Released Particle Properties section of the Settings window for Release from Grid.
Example: Coulombic Attraction Between Ions and Electrons
To model the Coulomb interaction between ions and electrons, use the Charged Particle Tracing interface and take the following steps:
1
In the Model Builder window, under the Charged Particle Tracing (cpt) interface click the default Particle Properties node.
2
Optionally, type Electrons in the Label text field to make the Particle Properties node more descriptive.
3
Note that the default value for the Particle mass mp is me_const, a built-in physical constant for the electron mass. The default value for the Charge number Z is -1. Both of these values can be left as their defaults because they apply to electrons.
4
On the Physics toolbar, click Global and choose Particle Properties.
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Optionally, type Protons in the Label text field.
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For the Particle mass mp enter mp_const, a built-in physical constant for the proton mass. For the Charge number Z enter 1.
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On the Physics toolbar, click Global and choose Release from Grid.
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Optionally, type Electron Release in the Label text field.
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Enter in the initial position and velocity of the electron.
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Click to expand the Released Particle Properties section. Note that the first species, Electrons, is selected by default.
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On the Physics toolbar, click Global and choose Release from Grid.
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Optionally, type Proton Release in the Label text field.
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Enter in the initial position and velocity of the proton.
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From the Released particle properties list, select Protons.
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On the Physics toolbar, click Domains and choose Particle-Particle Interaction.
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Select all domains. By default, Coulomb is selected from the Interaction Force list.
When the study is run, one electron and one proton will be released, and these two particles will be attracted to each other.