This command is used to define the thermal radiation interaction between surfaces. The radiating power $q$ per unit area from a surface is defined as:

$\displaystyle{q = \varepsilon \sigma T^4}$

where $\varepsilon$ is the emissivity (defined in PROP_THERMAL), $\sigma$ is the Stefan-Boltzmann constant and $T$ is the absolute temperature. Radiating energy can be absorbed by (and partially reflected from) surrounding surfaces that are in line-of-sight. The emissivity of a receiving surface controls the energy that is absorbed. Reflected energy can be transferred to surrounding faces that are in line-of-sight.

The ambient temperature $T_{amb}$ constitutes an external (background) heat source.

Thermal radiation

Thermal radiation and interaction between a hot and a cold plate. The emissivity of the cold plate is low and a significant amount of energy is reflected back to the hot plate. Hence, the back face of the hot plate cools off quicker than the front face.