About the Heat Transfer Interfaces COMSOL Multiphysics includes the following interfaces for heat transfer: • Heat Transfer in Solids • Heat Transfer in Fluids • Joule Heating (multiphysics interface) They are used to compute the temperature field. The Joule Heating interface also computes an electric potential field. The main dependent variable is the temperature, T. The heat transfer interfaces and the multiphysics couplings can be used for modeling heat transfer by conduction and convection as well as conjugate heat transfer and electromagnetic heating.