Semi-Transparent Surface (Surface-to-Surface Radiation Interface)

This node is a variant of the Opaque Surface (Surface-to-Surface Radiation Interface) node. In addition to specular and diffuse reflection, specular transmission can be also considered on the surface. It is available when the is set to in the Surface-to-Surface Radiation interface settings. The node adds a radiosity shape function for each spectral band to its selection and uses it as surface radiosity.

It no radiation is transmitted through the surface, use the Opaque Surface (Surface-to-Surface Radiation Interface) node instead.

Radiation is supposed to occur on both sides of the surface.

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 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 is . 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 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 button (

), and in the node under , set a value for the in the section.

These settings are the same as for the Diffuse Surface (Surface-to-Surface Radiation Interface) node.

If is :

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By default, the ε (dimensionless), ρs (dimensionless), and τ (dimensionless) use values . 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 , set values or expressions. You may set temperature-dependent emissivity and reflectivity through the use of the variable rad.T.

Select the , , and check boxes to set specific values on each side. The , , , , , and should be set.

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By default, the ε (dimensionless), ρs (dimensionless), and τ (dimensionless) use values .

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When is set to , enter a value or expression for the 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 option to avoid the evaluation of the average.

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When is set to , enter a value or expression for the 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 option to avoid the evaluation of the average.

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When is set to , enter a value or expression for the τ. The wavelength may be accessed through the rad.lambda variable. Any expression set for the transmissivity is then averaged on each spectral band to obtain a piecewise constant transmissivity. If the average value of the transmissivity on each band is known, you may use instead the option to avoid the evaluation of the average.

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When is set to , enter a value for the for each spectral band. Within a spectral band, each value is supposed to be wavelength-independent. By default, the same emissivity is defined on both sides. Select the check box and fill the and columns of the table for a specific definition on each side.

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When is set to , enter a value for the for each spectral band. Within a spectral band, each value is supposed to be wavelength-independent. By default, the same reflectivity is defined on both sides. Select the check box and fill the and columns of the table for a specific definition on each side.

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When is set to , enter a value for the for each spectral band. Within a spectral band, each value is supposed to be wavelength-independent. By default, the same transmissivity is defined on both sides. Select the check box and fill the and 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.

Set the surface transmissivity to a number between 0 and 1, where 0 applies to an opaque surface and 1 is appropriate for a fully transparent surface.

Set a value or expression for the θc, which is the minimum angle of incidence (measured between the ray and the normal to the surface) for transmission to occur. Below this angle, all the radiation is reflected. The pi/2 default value ensures that total reflection does not occur by default. Select the check box to set specific values on each side.

When the is set to for a spectral band, the information set for this spectral band in this section is not used.