Define Participating Media External Boundaries
Use the External Boundary tool to define diffusion and refractive properties of wall surfaces of participating media.
- 
                From the Radiation ribbon, click the
                        External Boundary tool.
                

Figure 1. - 
                Select interface surfaces between participating media model solids and external
                    environments.
                
- You can only select wall surfaces of participating media solids which are exposed to external environments (not connected to other participating or non-participating media).
 - If the physics model is not set to P1 or DO, you will not be allowed to select any surfaces.
 - If interface surfaces are not selected, they will be automatically assigned with the default properties set in the Thermal Radiation Physics tool.
 
 - In the microdialog, define the diffused fraction, specular ordinate averaging method, refractive index, and external temperature.
 - 
                From the guide bar, execute the command in the following
                    ways:
                
- Click 
 to confirm your selection and remain in the
                            tool.This allows you to continue creating instances and helps you visualize and edit instances with the legend.
 - Click 
 to confirm your selection and exit the
                        tool. 
 - Click