Benefits of the Different Heat Transfer Interfaces
The benefit of the different versions of the Heat Transfer interface, with ht as the common default name (see Heat Transfer Variables), is that it is easy to add the default settings when selecting the physics interface. At any time, add a Fluid or Solid node from the Physics toolbar — the functionality is always available.
Also see The Heat Transfer in Pipes Interface in the Pipe Flow Module User’s Guide for simulating heat transfer in pipe networks, including wall heat transfer to the surroundings.