Study 2
In order to keep the previous solution and to be able to compare it with this version of the model, rename the first study for clarity and add a second stationary study.
1
In the Model Builder window, select Study 1 node and, in the Settings window, rename it Study 1 Without Radiation.
2
In the Model Builder window, under Study 1 Without Radiation click Step 1: Stationary.
3
In the Settings window for Stationary, locate the Physics and Variables Selection section.
4
In the table, clear the Solve for checkbox for Surface-to-Surface Radiation (rad).
5
In the table, clear the Solve for checkbox for Heat Transfer with Surface-to-Surface Radiation 1 (htrad1).
6
In the Home toolbar, click Add Study .
7
In the Add Study window, select General Studies > Stationary .
8
Click Add Study .
9
Click Add Study button  again to close the Add Study panel.
10
Select Study 2 node and, in the Settings window, rename it Study 2 With Radiation.
11
In the Home toolbar, click Compute .