Surface Materials Model Reference

Reflection specularity is the specular fraction of the surface reflectivity:

• A value of 0 denotes that all of the reflection is diffuse.
• A value of 1 denotes that all of the reflection is specular.
• A value in between denotes a combination of diffuse and specular reflection.

Reflectivity is the ratio of reflected radiant energy over incident radiant energy at a given surface (dimensionless). Corresponds to ${\rho }_{\lambda }$ in Eqn. (1765).

By default, Reflectivity is calculated automatically using the Auto-Calculate method. When this method is selected, the reflectivity is calculated automatically from the specified emissivity and transmissivity values using Kirchhoff's law (­reflectivity = 1 -­­ emissivity - transmissivity). If you specify reflectivity using a scalar profile, you must ensure Kirchhoff's law is satisfied. The only time the Auto-Calculate method must not be used is in the special situation where Kirchhoff's law is explicitly deactivated (see The Gray Thermal Radiation Model).

For the Multiband spectrum model, values of this property can be specified for each spectral band.

Transmissivity is the ratio of transmitted radiant energy over incident radiant energy at a given surface (dimensionless). Corresponds to ${\tau }_{\lambda }$ in Eqn. (1764).

Transmissivity must be same on both sides of an interface.

If radiation or spectrum models do not match on both sides of an interface, that interface does not have any transmissivity input and is treated as opaque. The only exception is the boundary of a volume region when the Fluid Film and Surface-to-Surface Radiation models are selected. In that case, the boundary on the volume region side of the fluid film interface has transmissivity input instead of the interface. Radiation is not active on the fluid film region side.

Transmissivity becomes available in both interface boundaries when a Baffle or Porous Baffle interface is created, provided a radiative transfer model (Surface-to-Surface Radiation or Participating Media Radiation) is selected in the regions on both sides of the interface.