Settings for the Radiation in Participating Media Interface
The Label is the default physics interface name.
The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first physics interface in the model) is rpm.
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Radiative Heat Transfer in Finite Cylindrical Media: Application Library path Heat_Transfer_Module/Verification_Examples/cylinder_participating_media
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Radiative Heat Transfer in a Utility Boiler: Application Library path Heat_Transfer_Module/Thermal_Radiation/boiler
Participating Media Settings
Wavelength Dependence of Radiative Properties
Define the Wavelength dependence of radiative properties:
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Keep the default value, Constant, to define a gray radiation model. In this case, the radiative properties (emissivity, absorption and scattering coefficients) have the same definition for all wavelengths. These properties can still depend on other quantities, in particular on the temperature.
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Select Solar and ambient to define a spectral radiation model with two spectral bands, one for short wavelengths, [0, λsol/amb], (solar radiation) and one for large wavelengths, [λsol/amb, +∞[, (ambient radiation). It is then possible to define the Separation point between spectral bands (SI unit: m), λsol/amb, to adjust the wavelength intervals corresponding to the solar and ambient radiation. The radiative properties can then be defined for each spectral band.
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Select Multiple spectral bands and set the value of the Right endpoint for each spectral band in the table, to define a spectral radiation model. The value of the Right endpoint must be entered without unit. Modify the Wavelength unit to set the unit of all the endpoints. Right endpoint values should be set in an ascending order. The values of the Left endpoint for the next spectral band are updated automatically. It is possible to provide a definition of the surface properties for each spectral band.
The first Left endpoint and the last Right endpoint are predefined and equal to 0 and +∞, respectively.
Parameters can be used to set the value of the Right endpoint.
The wavelengths λ set in Solar and ambient and Multiple spectral bands are the wavelengths in vacuum.
Radiation Discretization Method
Select a Radiation discretization method: Discrete ordinates method (the default), or P1 approximation.
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When Discrete ordinates method is selected, Opaque Surface (Radiation in Participating Media and Radiation in Absorbing-Scattering Media Interfaces) and Continuity on Interior Boundary (Radiation in Participating Media and Radiation in Absorbing-Scattering Media Interfaces) are automatically added as default features.
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When P1 approximation is selected, Opaque Surface (Radiation in Participating Media and Radiation in Absorbing-Scattering Media Interfaces) is automatically added as a default feature and both this and Incident Intensity (Radiation in Participating Media and Radiation in Absorbing-Scattering Media Interfaces) are made available from the Physics ribbon toolbar (Windows users), Physics context menu (Mac or Linux users), or the context menu (all users). Continuity on Interior Boundary (Radiation in Participating Media and Radiation in Absorbing-Scattering Media Interfaces) is not available.
The choice of Radiation discretization method also offers different settings for the Participating Medium (Radiation in Participating Media Interface) (all methods), Opaque Surface (Radiation in Participating Media and Radiation in Absorbing-Scattering Media Interfaces) (P1 approximation), and Incident Intensity (Radiation in Participating Media and Radiation in Absorbing-Scattering Media Interfaces) (P1 approximation) nodes.
Refractive Index
For either selection, define the Refractive index nr (dimensionless) of the participating media. The same refractive index is used for the whole model.
Performance Index
When Discrete ordinates method is selected, choose a Performance index Pindex from the list. Select a value between 0 and 1 that modifies the strategy used to define automatic solver settings. The default is 0.4. With small values, a robust setting for the solver is expected. With large values (up to 1), less memory is needed to solve the model.
Quadrature Set
When Discrete ordinates method is selected, the method of angular discretization of the radiative intensity direction should be specified. In particular, it defines the method of computation of the weights wj used in the approximation of the scattering term:
Choose a Quadrature set from the list:
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The Level Symmetric Even (the default), Level Symmetric Hybrid, and Equal Weight Odd sets are SN approximations. Depending on the set and the order selected in the Discrete ordinates method list, different moment conditions are satisfied. In 3D, S2, S4, S6, and S8 generate 8, 24, 48, and 80 directions, respectively. In 2D, S2, S4, S6, and S8 generate 4, 12, 24, and 40 directions, respectively.
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The Quasi-uniform weight approximation discretizes the angular space by using a reference octahedron with 8 triangular faces, further discretized in function of the order of the method. This corresponds to a TN approximation, for which 8N2weights are computed at order N.
See Discrete Ordinates Method (DOM) for details about the SN and TN quadrature sets.
Discretization
Radiative Intensity
When the Radiation discretization method is set to Discrete ordinates method in Participating Media Settings, set the discretization level of the Radiative intensity: Constant, Linear (the default), Quadratic, Cubic, Quartic, or Quintic.
Incident Radiation
When the Radiation discretization method is set to P1 approximation in Participating Media Settings, set the discretization level of the Incident radiation: Linear (the default), Quadratic, Cubic, Quartic, or Quintic.