The Conjugate Heat Transfer, Laminar Flow and Turbulent Flow Interfaces
When a multiphysics interface is added from the Heat Transfer>Conjugate Heat Transfer branch  of the Model Wizard or Add Physics windows, Heat Transfer and one of the Single-Phase Flow interfaces (laminar or turbulent flow) are added to the Model Builder.
In addition, the Multiphysics node is added, which includes the multiphysics coupling feature Nonisothermal Flow.
The Multiphysics Node in the COMSOL Multiphysics Reference Manual.
The Laminar Flow interface () combines a Heat Transfer interface with a Laminar Flow interface.
The Turbulent Flow, Algebraic yPlus interface () combines a Heat Transfer interface with a Turbulent Flow, Algebraic yPlus interface.
The Turbulent Flow, L-VEL interface () combines a Heat Transfer interface with a Turbulent Flow, L-VEL interface. The Turbulent Flow, k-ε interface () combines a Heat Transfer interface with a Turbulent Flow, k-ε interface.
The Turbulent Flow, Low Re k-ε interface () combines a Heat Transfer interface with a Turbulent Flow, Low Re k-ε interface.