Heat Transfer Module

New Functionality in Version 4.3

• A new boundary condition, Interior Wall, is available on interior boundaries in the Conjugate Heat Transfer and Non-Isothermal Flow interfaces. It makes it possible to define a wall condition between two fluid domains. This is especially useful to model thin walls as boundaries. You no longer need to define a solid domain with a wall boundary condition on both sides, which can result in a dense mesh. This boundary condition implements wall functions when using the k-ε or k-ω turbulence model.

• A new parameter, the refractive index, is available in interfaces including radiation in participating media. This parameter makes it possible to define a refractive index different than one like in liquids (for example, water) or solids (for example, glass).

• A new option, solar position, is available to define external radiation source in 3D for all interfaces including surface-to-surface radiation features. This option provides a convenient way to define the direction and intensity of the incident radiation coming from the Sun from the position on the Earth, the date, and the time.

• New choices are available to define the total heat source or the total heat flux in Line Heat Source, Layer Heat Source, and Edge Heat Flux features. These options simplify the definition of models where the total heat source or heat flux is known because you no longer have to convert it into heat flux (or heat source) per surface area or length.

• The surface-to-surface radiation features are now available in the Thin Conductive Shell interface. This is especially useful to model radiative heat transfer between thin structures.

• The previous infinite elements feature has been removed. The Heat Transfer interfaces uses the Infinite Element Domain defined in the Definitions>Domain Properties section. This simplifies the definition of the infinite domains when a model includes multiple physics.

• The inflow heat flux boundary condition has been improved so that heat transport into the domain is controlled by the flow convection. This change prevents unphysical results like computing high temperatures in no-flow parts of inflow heat flux boundaries.

• Enthalpy and internal energy are now calculated using state integrals. This gives increased accuracy for heat and energy balances.

• A new material, humid air, is available in the Liquids and Gases material library.

Backward Compatibility vs. 4.2a

• The Fan, Grille, and Vacuum Pump features are now separate features instead of options in the Inlet and Outlet features.

• Due to the new Inflow Heat Flux boundary condition behavior, the results of models using it are affected. This should lead to better physical results. It is, however, possible to add a compensation flux to the model to retrieve the old behavior. Please contact COMSOL’s technical support for this purpose.

• The degrees of freedom used for radiative intensities are now internal degrees of freedom of the heat transfer interfaces. This affects all interfaces containing radiation in participating media features except the standalone Radiation in Participating Media interface. The names of the internal degrees of freedom start by the physics interface identifier followed by In, where n is the index of the radiative intensity direction (for example, ht.I1, ht.I2, ...). This change requires updates of the variable names if they have been explicitly used in the model, study, or results nodes.

• In order to avoid conflict in the name of feature internal variables, the feature prefix has been added to the scope of some variables. The list of all feature internal variables and their definition is available in the Equation View node of each feature.

• The sign of the constraint for temperature has been changed to match the convention used in other physics. This has no effect on the models unless weak constraints are used. In that case, the Lagrange multipliers sign is changed.

• The default arrow plot in Heat Transfer interfaces now shows the total heat flux instead of the temperature gradient which has opposite sign for purely conductive heat transfer models.

• Heat Continuity and Periodicity features from Non-Isothermal flow interface have been updated to support wall function when using a k-ε or k-ω turbulence model.

Backward Compatibility vs. 3.5a

K-ω Turbulence Model

The Turbulent Flow, k-ω physics interface is part of the CFD Module in version 4.3.

Turbulent Flow with Wall Functions and Heat Transfer in Conjugate Heat Transfer

Momentum transport Wall Functions are translated into the revised Wall Functions in version 4.3. The Heat equation Wall Functions are also translated, but the translated formulation uses the default turbulence modeling constants, regardless of the values that were defined in Physics>Scalar Variables in 3.5a.