Set the Node name for the radiative heat rate node.

The heat rate P due to radiation on a diffuse-gray surface from the ambient surrounding is:

where σ is the Stefan-Boltzmann constant, ε is the emissivity of the surface, A is the area of the surface, Tamb is the ambient temperature, and T is the surface temperature.

In the thermal system, the corresponding heat rate applied on the selected node can be expressed in function of the difference between the ambient temperature, Tamb and the node temperature, T, by mean of the radiative thermal resistance, Rrad:

First, set the surface Area A. Then, select any material from the Material list to define the Surface emissivity ε From material. For User defined enter a value or expression.

Finally, set the Ambient temperature, Tamb. For User defined, enter a value or expression. Else, select an Ambient temperature defined in an Ambient Properties node under Definitions.

Select appropriate options in the Add the following to default results in order to include the following global variables (space-independent) in the default plots:

Physics Tab with Lumped Thermal System selected: