The Nonisothermal Flow and Conjugate Heat Transfer interfaces combine the heat equation with laminar flow in a Fluid domain. The coupling with turbulent flow in Fluid, Porous Medium, and Moist Air domain models is available with add-on modules. The advantage of using the multiphysics interfaces is that predefined couplings are available in both directions. In particular, physics interfaces use the same definition of the density, which can therefore be a function of both pressure and temperature. Solving this coupled system of equations usually requires numerical stabilization accounting for the couplings, which the predefined multiphysics interfaces also set up.

When a multiphysics interface is added from the Heat Transfer>Conjugate Heat Transfer branch or the Fluid Flow>Nonisothermal Flow branch  of the Model Wizard or Add Physics windows, the Single-Phase Flow interface (laminar flow) and a Heat Transfer interface are added to the Model Builder. In addition, the Multiphysics node is added, which includes the multiphysics coupling feature Nonisothermal Flow.