Opaque Surface (Surface-to-Surface Radiation interface)
This node is a variant of the Diffuse Surface (Surface-to-Surface Radiation interface) node with specular reflectivity. It is available when the Surface-to-surface radiation method is set to Ray shooting in the Surface-to-Surface Radiation interface settings. It applies on glossy surfaces on which specular radiation should be considered in addition to diffuse radiation. The node adds radiosity shape function for each spectral band to its selection and uses it as surface radiosity.
If only diffuse reflection should be considered, use the Diffuse Surface (Surface-to-Surface Radiation interface) node instead.
It is supposed that no radiation is transmitted through the surface. If radiative transmission should be also considered, use the Semi-Transparent Surface (Surface-to-Surface Radiation interface) node instead.
Model Input
This section has fields and values that are inputs to expressions that define material properties. If such user-defined property groups have been added, the model inputs are included here.
There is one standard model input: the Temperature T is used in the expression of the blackbody radiation intensity and when multiple wavelength intervals are used, for the fractional emissive power. The temperature model input is also used to determine the variable that receives the radiative heat source. When the model input does not contain a dependent variable, the radiative heat source is ignored.
The default Temperature is User defined. When additional physics interfaces are added to the model, the temperature variables defined by these physics interfaces can also be selected from the list. The Common model input option corresponds to the minput.T variable, set to 293.15 [K] by default) and all temperature variables from the physics interfaces included in the model. To edit the minput.T variable, click the Go to Source button (), and in the Common Model Inputs node under Global Definitions, set a value for the Temperature in the Expression for remaining selection section.
Radiation Direction
These settings are the same as for the Diffuse Surface (Surface-to-Surface Radiation interface) node.
Ambient
These settings are the same as for the Diffuse Surface (Surface-to-Surface Radiation interface) node.
Fractional Emissive Power
These settings are the same as for the Diffuse Surface (Surface-to-Surface Radiation interface) node.
Surface Radiative Properties
If Wavelength dependence of surface properties is Constant:
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By default, the Surface emissivity ε (dimensionless) and Surface reflectivity ρs (dimensionless) use values From material. These are properties of the material surface that depend both on the material itself and the structure of the surface. Make sure that a material is defined at the boundary level (by default materials are defined at the domain level).
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For User defined, set values or expressions. You may set temperature-dependent emissivity and reflectivity through the use of the variable rad.T.
Select the Define surface emissivity on each sides and Define surface reflectivity on each sides check boxes to set specific values on each side. The Surface emissivity, upside, Surface emissivity, downside, Surface reflectivity, upside, and Surface reflectivity, downside should be set.
If Wavelength dependence of surface properties is Solar and ambient or Multiple spectral bands:
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By default, the Surface emissivity ε (dimensionless) and Surface reflectivity ρs (dimensionless) use values From material.
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When Surface reflectivity is set to User defined, enter a value or expression for the Surface reflectivity ρs. The wavelength may be accessed through the rad.lambda variable. Any expression set for the reflectivity is then averaged on each spectral band to obtain a piecewise constant reflectivity. If the average value of the reflectivity on each band is known, you may use instead the User defined for each band option to avoid the evaluation of the average.
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When Surface emissivity is set to User defined, enter a value or expression for the Surface emissivity ε. The wavelength may be accessed through the rad.lambda variable. Any expression set for the emissivity is then averaged on each spectral band to obtain a piecewise constant emissivity. If the average value of the emissivity on each band is known, you may use instead the User defined for each band option to avoid the evaluation of the average.
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When Surface emissivity is set to User defined for each band, enter a value for the Surface emissivity for each spectral band. By default, the same emissivity is defined on both sides. Select the Define initial surface emissivity on each side check box and fill the Upside and Downside columns of the table for a specific definition on each side.
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When Surface reflectivity is set to User defined for each band, enter a value for the Surface reflectivity for each spectral band. By default, the same reflectivity is defined on both sides. Select the Define initial surface reflectivity on each side check box and fill the Upside and Downside columns of the table for a specific definition on each side.
Set the surface emissivity  to a number between 0 and 1, where 0 represents diffuse mirror and 1 is appropriate for a perfect blackbody. The proper value for a physical material lies somewhere in-between and can be found from tables or measurements.
Set the surface reflectivity  to a number between 0 and 1, where 0 applies to a perfect diffuse surface and 1 is appropriate when reflection is only specular.
When the Radiation direction is set to None for a spectral band, the information set for this spectral band in this section is not used.
If this feature is combined with heat transfer in 2D and 1D, the thickness is assumed to be infinite for the view factor computation. The user-defined value for dz is still used in the heat transfer equation.
Location in User Interface
Context menus
 Surface-to-Surface Radiation>Opaque Surface
Ribbon
Physics Tab with Surface-to-Surface Radiation selected:
Boundaries>Surface-to-Surface Radiation>Opaque Surface