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 settings of the Surface-to-Surface Radiation interface. It applies to glossy surfaces where specular radiation should be considered in addition to diffuse radiation. The node adds to its selection a radiosity shape function for each spectral band, and uses it as surface radiosity.
If only diffuse reflection is to be taken into account, use the Diffuse Surface (Surface-to-Surface Radiation Interface) node instead.
It is assumed that no radiation is transmitted through the surface. If radiative transmission is also to be taken into account, use the Semitransparent 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 Default Model Inputs node under Global Definitions, set a value for the Temperature in the Expression for remaining selection section.
Coordinate System Selection
Select a boundary system from the Coordinate system list to define the reference vector for the azimuthal angle. The first component of the boundary system selected is the reference vector used for directional surface properties. The default is the boundary system of the model, and the list contains any additional boundary system added under the Definitions node.
See Coordinate Systems in the COMSOL Multiphysics Reference Manual for more details.
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
Directional Dependence
By default, the Directional dependence of the surface emissivity is set to Constant. The Emissivity can be defined by an expression depending on other variables such as temperature or spatial coordinates. Switch to the Polar or Polar and azimuthal options to define the dependencies on the polar and azimuthal angles (θ and φ, respectively) by specifying a Directional emissivity function, fε. When using the Polar option, select from the Directional emissivity function list any function of one argument already defined in the component, under the Definitions node. For the Polar and azimuthal option, select from the functions of two arguments. By default, only the Zero function is available in the list, defining fε(θ) = 0 or fεφ) = 0.
The other dependencies (temperature T, spatial coordinates x) are treated separately in the Emissivity expression, and used to define the total emissivity:
Select the Define properties on each side check box to define specific directional dependencies of the surface emissivity on each side of the boundary, and set the Directional dependence, upside and Directional dependence, downside accordingly.
The reference vector for the azimuthal angle is given by the first component of the Coordinate system selected in the Coordinate System Selection section.
Emissivity, Directional Emissivity Function, and Diffuse Reflectivity
If the Wavelength dependence of radiative properties is Constant:
By default, Emissivity ε (dimensionless) and Diffuse reflectivity ρd (dimensionless) use values From material. These are properties of the 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).
For User defined, set values or expressions. You can define the emissivity and reflectivity as functions of temperature using the variable rad.T.
Select the Define properties on each side check box to define specific values for each side. Select the Boundary material, upside and Boundary material, downside to have different material properties on each side. The boundary material specified is used only when Emissivity, upside, Emissivity, downside, Diffuse reflectivity, upside, and Diffuse reflectivity, downside are From material.
If the Wavelength dependence of radiative properties is Solar and ambient or Multiple spectral bands:
By default, the Emissivity ε (dimensionless) and Diffuse reflectivity ρd (dimensionless) use values From material.
When Emissivity is User defined, enter a value or expression for Emissivity ε. The wavelength is accessible through the rad.lambda variable. Any expression set for the emissivity is then averaged over each spectral band to obtain a piecewise constant emissivity. If the average value of the emissivity on each band is known, you can use instead the User defined for each band option to avoid the evaluation of the average.
When Diffuse reflectivity is User defined, enter a value or expression for the Diffuse reflectivity ρd. The wavelength is accessible 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.
When Emissivity is User defined for each band, enter a value for the Emissivity for each spectral band. Within a spectral band, each value is assumed to be independent of wavelength. By default, the same emissivity is set on both sides. Select the Define properties on each side check box and fill the Upside and Downside columns of the table for a specific definition on each side.
When Diffuse reflectivity is User defined for each band, enter a value for the Diffuse reflectivity for each spectral band. Within a spectral band, each value is assumed to be independent of wavelength. By default, the same reflectivity is defined on both sides. Select the Define properties 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 a diffuse mirror and 1 is suitable for a perfect blackbody. The appropriate value for a physical material is somewhere in between and can be found in tables or measurements.
Set the diffuse reflectivity of the surface to a number between 0 and 1, where 1 applies to a perfect diffuse surface and 0 is appropriate when the reflection is only specular.
The specular surface reflectivity, ρs, is then defined as
When the Emitted radiation direction is set to None for a spectral band, the information defined for that spectral band in this section is not used.
Location in User Interface
Context Menus
Ribbon
Physics tab with Surface-to-Surface Radiation selected: