The Heat Transfer Module has multiphysics couplings available under certain conditions.
When a predefined multiphysics interface is added from the Model Wizard or
Add Physics windows, it adds the constituent interfaces and the
Multiphysics node, which automatically includes one or more multiphysics couplings.
If the constituent physics interfaces are added one at a time, then it adds an empty Multiphysics node. When you right-click this node, you can choose from the available multiphysics couplings.
See The Heat Transfer Module Interfaces for details about the Heat Transfer Module interfaces.
See Multiphysics Interfaces for details about the predefined multiphysics interfaces of the Heat Transfer Module.