The Heat Transfer in Fluids (ht) interface () is used to model heat transfer in fluids by conduction, convection, and radiation. A Fluid model is active by default on all domains. All functionality for including other domain types, such as a solid domain, is also available.

When this version of the physics interface is added, these default nodes are added to the Model Builder: Fluid, Thermal Insulation (the default boundary condition), and Initial Values. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions and sources. You can also right-click Heat Transfer in Fluids to select physics features from the context menu.

By default, the shape functions used for the temperature in fluids are Linear.