To Define Radiation Condition
1. Click > 
Radiation Condition. The Radiation Condition dialog box opens.
Radiation Condition. The Radiation Condition dialog box opens.2. Type a name for the boundary condition or accept the default name.
3. Select an existing boundary condition set from the Member of Set list, or click New to display the BC Set Definition dialog box and create a new boundary condition set.
4. Select the surfaces associated with the radiation. You can select Individual, Boundary or Intent surfaces of your model. You can also select a surface set. If you have already selected the geometric entity before opening the Radiation Condition dialog box, your selection appears in the References collector when the dialog box opens.
5. Click Advanced to display the Spatial Variation and Temperature Dependence options of Emissivity (Ɛ).
6. Specify the Spatial Variation for emissivity (ε).
7. Select the Function of Temperature option from the Temperature Dependence drop-down list if you want emissivity to vary as a function of temperature. The Radiation Condition dialog box expands to display the 
button. Click this button to open the Function Definition dialog box. Specify the function over the temperature range.
button. Click this button to open the Function Definition dialog box. Specify the function over the temperature range.8. Type a value between 0 and 1 for the emissivity (ε) in the Value box.
9. Type a real number value for the Ambient Temperature in the Value box. Select the units from the drop-down list or accept the default unit.
10. Click Preview Ɛ to check the spatial variation of emissivity (ε).
11. Click OK.
Return to Radiation Conditions.