The Joule Heating Interface

The Joule Heating () interface is used to model resistive heating and, depending on additional licensed products, dielectric heating in devices where inductive effects are negligible; that is, when the skin depth is much larger than the studied device. This multiphysics interface adds an Electric Currents interface and a Heat Transfer in Solids interface. The multiphysics couplings add the electromagnetic power dissipation as a heat source, and the electromagnetic material properties can depend on the temperature.

Depending on the licensed products, stationary modeling, time-domain modeling are supported in all space dimensions. In addition, combinations of frequency-domain modeling for the Electric Currents interface and stationary modeling for the Heat Transfer in Solids interface, called frequency-stationary and frequency-transient modeling, are supported.

When a predefined Joule Heating interface is added from the Heat Transfer>Electromagnetic Heating branch () of the Model Wizard or Add Physics windows, Electric Currents and Heat Transfer in Solids interfaces are added to the Model Builder. In addition, The Multiphysics Node is added, which automatically includes the multiphysics coupling features Electromagnetic Heat Source, Boundary Electromagnetic Heat Source, and Temperature Coupling.

On the Constituent Physics Interfaces

The Electric Currents interface computes electric field, current and potential distributions in conducting media under conditions where inductive effects are negligible; that is, when the skin depth is much larger than the studied device. Depending on the licensed products, time and frequency domain formulations that account for capacitive effects are also provided. The Electric Currents interface solves a current conservation equation based on Ohm's law using the scalar electric potential as the dependent variable.

The Heat Transfer in Solids interface provides features for modeling heat transfer by conduction, convection, and radiation. A Heat Transfer in Solids model is active by default on all domains. All functionality for including other domain types, such as a fluid domain, is also available. The temperature equation defined in solid domains corresponds to the differential form of the Fourier's law that may contain additional contributions like heat sources.

In previous versions of COMSOL Multiphysics, a specific physics interface called Joule Heating was added to the Model Builder. Now, a predefined multiphysics coupling approach is used, improving the flexibility and design options for your modeling. For specific details, see Multiphysics Modeling Approaches.

Settings for Physics Interfaces and Coupling Features

When physics interfaces are added using the predefined couplings, for example Joule Heating, specific settings are included with the physics interfaces and the coupling features.

However, if physics interfaces are added one at a time, followed by the coupling features, these modified settings are not automatically included.

For example, if single Electric Currents and Heat Transfer in Solids interfaces are added, COMSOL adds an empty Multiphysics node. When you right-click this node, you can choose from the available coupling features, Electromagnetic Heat Source, Boundary Electromagnetic Heat Source, and Temperature Coupling, but the modified settings are not included.

Table 14-1: Modified Settings for a Joule Heating interface

Physics or Coupling Interface	Modified Settings (if Any)
Electric Currents	No changes.
Heat Transfer in Solids	No changes.
Electromagnetic Heat Source	The Domain Selection is the same as that of the participating physics interfaces. The corresponding Electric Currents and Heat Transfer in Solids interfaces are preselected in the Electromagnetic Heat Source section.
Boundary Electromagnetic Heat Source	The Boundary Selection contains all boundaries of the participating physics interfaces. The corresponding Electric Currents and Heat Transfer in Solids interfaces are preselected in the Boundary Electromagnetic Heat Source section.
Temperature Coupling	The corresponding Electric Currents and Heat Transfer in Solids interfaces are preselected in the Temperature Coupling section.

Physics Interface and Coupling Features

Coupling Features

The Electromagnetic Heat Source, Boundary Electromagnetic Heat Source, and Temperature Coupling multiphysics coupling nodes are described in this section.

Physics Interface Features

Physics nodes are available from the Physics ribbon toolbar (Windows users), Physics context menu (Mac or Linux users), or right-click to access the context menu (all users).

In general, to add a node, go to the Physics toolbar, no matter what operating system you are using.

•	The available physics features for the heat transfer interfaces are listed in the sections Domain Features, Boundary Features, and Edge and Point Features.

•	For information about the available physics features for the Electric Currents interface, see The Electric Currents Interface.

If you have an add-on module, such as the Heat Transfer Module or AC/DC Module, there are additional specialized physics nodes available and described in the individual module documentation.

Thermal Microactuator Simplified: Application Library path COMSOL_Multiphysics/Multiphysics/thermal_actuator_simplified