Thermophoretic Force
Use the Thermophoretic Force node to exert the thermophoretic force on particles. The phenomenon called thermophoresis causes particles to migrate in a fluid with a nonuniform temperature field.
Supported formulations:
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Newtonian,
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Newtonian, first order, and
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Newtonian, ignore inertial terms.
Model Input
The model inputs for the Temperature T (SI unit: K) and Absolute pressure pA (SI unit: Pa) are always shown in the settings window for this feature, even if there are no material properties that depend on them.
Fluid Properties
If the Include rarefaction effects check box is selected in the physics interface Particle Release and Propagation section, select an option from the Thermophoretic force model list. Some of these options are only applicable for certain Knudsen number ranges:
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The Epstein model is valid for continuum flows (Kn << 1). That is, the mean free path of molecules in the fluid should be much smaller than the particle diameter.
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The Waldmann, model is valid for free molecular flows (Kn >> 1).
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Talbot and Linearized BGK are usable over a wide range of Knudsen numbers.
When the Include rarefaction effects check box is cleared, the fluid is always treated as a continuum (low Knudsen number) flow, and only the Epstein model is used.
The following fluid parameters all take default values From material or can be computed from another physics interface. Or select User defined to enter a value or expression for the:
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Dynamic viscosity μ (SI unit: Pa·s). The default is 0.02 mPa s.
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Density ρ (SI unit: kg/m3). The default is 1 kg/m3.
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Thermal Conductivity k (SI unit: W/(m·K)). For User defined select Isotropic, Diagonal, Symmetric, or Full and then enter values in the field or matrix.
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Heat capacity at constant pressure Cp (SI unit: J/(kg K)).
The default is 1 kJ/(kg K).
If the Waldmann, Talbot, or Linearized BGK model is used, also enter the Background gas molar mass Mg (SI unit: kg/mol). The default is 0.04 kg/mol.
If the Waldmann, Talbot, or Linearized BGK model is used, select an option from the Mean free path calculation list: Ideal gas, hard sphere collisions or User-defined correction. For User-defined correction enter a Mean free path correction λ'/λ by which the mean free path differs from the value for hard spheres in an ideal gas.
If the Linearized BGK model is used, enter an Energy accommodation coefficient αE (dimensionless) and a Momentum accommodation coefficient αM (dimensionless). The default values are 1.
Particle Properties
Enter a value or expression for the Thermophoretic correction factor Cs (dimensionless). The default is 1.17. If the Talbot model is used, enter two additional dimensionless thermophoretic correction factors Cm and Ct. The default values are 1.146 and 2.2, respectively.
Advanced Settings
Select the Use piecewise polynomial recovery on field check box to smooth the temperature using piecewise polynomial recovery. This can give a much more accurate representation of the temperature as it uses information on adjacent mesh elements to reconstruct the field. If a coarse mesh is used to compute the field then this option can be especially useful.
Use the Particles to affect list to apply the force to specific particles. The available settings are the same as for the Force node.
Thermophoretic Force in the theory section.