Dielectric Window (Surface-to-Surface Radiation Interface)
This node aims to model the energy transfer through a thin dielectric layer. This layer defines a refractive index and an absorption coefficient. It calculates the directional dependent radiative properties such as emissivity, specular reflectivity, and transmissivity with Fresnel’s relations. It is available when the Surface-to-surface radiation method is set to Ray shooting in the Surface-to-Surface Radiation interface settings.
For faster computations, the Angular dependent properties option in the Surface-to-Surface Radiation interface settings can be set to Interpolated function.
This feature uses the Beer–Lambert law to model the absorption in the layer. The Beer–Lambert law is valid for a nonscattering and nonemitting medium. In this feature, in order to conserve the energy, the absorbed energy in the layer is ultimately re-emitted as blackbody/graybody radiation on each side of the boundary.
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. To edit the minput.T variable, click the Go to Source button (), and in the Default Model Inputs node under Global Definitions, set a value for the Temperature in the Expression for remaining selection section.
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.
Layer Properties
This section defines the Refractive index, the Layer thickness, and the Absorption coefficient through a chosen Optical attenuation model.
By default, the Layer thickness is set to 5 mm.
By default, the Optical attenuation model is set to Absorption coefficient. The absorption coefficient κ can then directly be defined. To set the absorption coefficient through an internal transmittance τi for a certain sample size, choose between the different Internal transmittance, X mm sample thickness options, where X can be 2, 5, 10 or 25.
If Wavelength dependence of radiative properties is Constant:
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By default, the Refractive index, Absorption coefficient, and Internal transmittance use values From material. 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.
If Wavelength dependence of radiative properties is Solar and ambient or Multiple spectral bands:
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By default, the Refractive index, Absorption coefficient, and Internal transmittance use values From material.
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When the Refractive index is set to User defined, enter a value or expression for the Refractive index n. The wavelength may be accessed through the rad.lambda variable. Any expression set for the refractive index is then averaged on each spectral band to obtain a piecewise constant refractive index. If the average value of the refractive index 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 the Absorption coefficient is set to User defined, enter a value or expression for the Absorption coefficient κ. The wavelength may be accessed through the rad.lambda variable. Any expression set for the absorption coefficient is then averaged on each spectral band to obtain a piecewise constant refractive index. If the average value of the absorption coefficient 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 the Internal transmittance is set to User defined, enter a value or expression for the Internal transmittance τi. The wavelength may be accessed through the rad.lambda variable. Any expression set for the internal transmittance is then averaged on each spectral band to obtain a piecewise constant refractive index. If the average value of the internal transmittance 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 the Refractive index is set to User defined for each band, enter a value for the Refractive index for each spectral band. Within a spectral band, each value is assumed to be independent of wavelength.
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When the Absorption coefficient is set to User defined for each band, enter a value for the Absorption coefficient for each spectral band. Within a spectral band, each value is assumed to be independent of wavelength.
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When the Internal transmittance is set to User defined for each band, enter a value for the Internal transmittance for each spectral band. Within a spectral band, each value is assumed to be independent of wavelength.
Even though the refractive index can be an expression, it is expected to be spatially constant per boundary. It can still vary with respect to the wavelength.
Deriving the Directional Dependence of Surface Properties for Dielectric Windows
Location in User Interface
Context Menus
Surface-to-Surface Radiation > Dielectric Window
Ribbon
Physics tab with Surface-to-Surface Radiation selected:
Boundaries > Surface-to-Surface Radiation > Dielectric Window