Opacity (Surface-to-Surface Radiation and Orbital Thermal Loads Interfaces)
This node enables to define the refractive index of the domain, and the surface-to-surface radiation direction on the surrounding boundaries. When several spectral bands are defined, the opacity can be set for all or only a selection of wavelengths.
When the Emitted radiation direction is defined by Opacity controlled in surface-to-surface boundary features (Diffuse Mirror (Surface-to-Surface Radiation Interface), Diffuse Surface (Surface-to-Surface Radiation Interface), Prescribed Radiosity (Surface-to-Surface Radiation Interface), Opaque Surface (Surface-to-Surface Radiation Interface), Specular Mirror (Surface-to-Surface Radiation Interface)), surface-to-surface radiation propagates in nonopaque domains. Alternatively the Emitted radiation direction can be defined using the normal orientation or on both sides of boundaries. In this case the Opacity node is ignored. Note that on boundaries where the Semitransparent Surface (Surface-to-Surface Radiation Interface) is applied, the Emitted radiation direction is Both sides, and the Opacity node is ignored.
By default, all the domains and the exterior of the Surface-to-Surface Radiation interface are considered as transparent. To set the exterior as opaque, change the Selection of the Opacity node to All voids in the Domain Selection section, and set it as Opaque. Depending on the geometry, an infinite void and several finite voids may be available for the selection. When the Heat Transfer with Surface-to-Surface Radiation multiphysics coupling is active, it controls the default opacity.
Opacity
Depending on the Wavelength dependence of radiative properties defined in the Radiation Settings section of the physics interface settings, different sections display underneath.
When Wavelength dependence of radiative properties is set to Constant, select Opaque (default) or Transparent to set the domain opacity type.
When Wavelength dependence of radiative properties is set to Solar and ambient or Multiple spectral bands:
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When Opacity is set to User-defined for all bands (default), set the opacity of the domain for all bands by selecting Opaque (default) or Transparent. Use this option if the transparency or opacity properties of the material are not wavelength dependent.
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When Opacity is set to User-defined for each band, set the opacity for each spectral band by selecting the corresponding checkbox in the Opaque column of the table. By default the checkbox is selected for all spectral bands. Defining an opacity for each spectral band makes it possible to build models where the transparency or opacity properties of the material defers between spectral bands.
When the domain is transparent for at least one spectral band, the refractive index of the domain can be set using the Transparent media refractive index input.
Select From material to set the refractive index from the domain material properties. Select From default (default) to use the default value defined in the physics node with Default transparent media refractive index. Select User defined to enter a value or an expression for the refractive index.
When Wavelength dependence of radiative properties is set to Solar and ambient or Multiple spectral bands, select User-defined for each band to set the refractive index for each spectral band for which the domain is transparent.
Because of the hypotheses inherent to surface-to-surface radiation, the refractive index can only spatially change at an interface. Within domains, it can vary with wavelength, but not with space.
On boundaries adjacent to transparent domains, the refractive index is used in the expression of blackbody irradiation when it needs to be defined.
If a Semitransparent Surface (Surface-to-Surface Radiation Interface), a Radiation Shield, Upside (Surface-to-Surface Radiation Interface) or a Dielectric Window (Surface-to-Surface Radiation Interface) feature is applied on a boundary between two domains or between a domain and a void of different refractive indices, then refraction is also accounted for. Note that these features are available when the Surface-to-surface radiation method is Ray shooting.
When refraction is accounted for, a critical angle is calculated from the Snell’s law. In the Semitransparent Surface (Surface-to-Surface Radiation Interface) feature, the effective critical angle used in computation is the minimum between the one from the Snell’s law, and the Surface critical angle input.
Free Convection in a Light Bulb: Application Library path Heat_Transfer_Module/Thermal_Radiation/light_bulb
Thermo-Photo-Voltaic Cell: Application Library path Heat_Transfer_Module/Thermal_Radiation/tpv_cell
Location in User Interface
Context Menus
Surface-to-Surface Radiation > Opacity
Ribbon
Physics tab with Surface-to-Surface Radiation selected in the model tree:
Domains > Opacity