# Heat transfer¶

The simulation type **Heat transfer** allows the calculation of the
temperature distribution and heat flux in a solid under thermal loads
as for example convection and radiation.

As a result you can analyse the temperature distribution in a steady state scenario as well as for example a transient heating process of a mechanical part. A negative heat flux over the borders of the domain illustrates the thermal power loss of e.g. a cooled device.

In the following the different simulation settings you have to define are described in detail as well as the various options you can add.

## Analysis Type¶

You can choose if you want to calculate the steady-state behavior of the system comparable to the Static analysis or if you want to take time dependent effects into consideration in a transient analysis.

## Domain¶

In order to perform an analysis a given geometrical domain you have to discretize your model by creating a mesh out of it. Details of CAD handling and Meshing are described in the Pre-processing section.

After you assigned a mesh to the simulation you can add some optional domain-related settings and have a look on the mesh details. Please note that if you have an assembly of multiple bodies that are not fused together, you have to add Contacts if you want to build connections between those independent parts.

### Materials¶

In order to define the material properties of the whole domain, you have to assign exactly one material to every part and define the thermal properties of those. Note that the specific heat is only needed for transient analyses.

### Initial Conditions¶

For a time dependent behaviour of a solid structure it is important to define the Initial Conditions carefully, since these values determine the solution of the analysis. If you chose to run a transient analysis the temperature depends on time. It is set to room temperature (293.15 K) by default and is also provided for steady-state simulations for convergence reasons.

### Boundary conditions¶

You can define temperature and thermal load boundary conditions. If you provide a temperature boundary condition on an entity, the temperature value of all contained nodes is set to the given prescribed value. Thermal load boundary conditions define the heatflux into or out of the domain via different mechanisms. Note that a negative heat flux indicates a heat loss to the environment. As a temperature boundary condition prescribes the temperature value on a given part of the domain it is not possible to simultaneously add a thermal load on that part as it would be overconstrained in that case.

Temperature boundary condition types (Thermal Constraints)

Heat flux boundary condition types (Thermal Loads)

## Numerics¶

Under numerics you can set the equation solver of your simulation. The choice highly influences the computational time and the required memory size of the simulation.

## Simulation Control¶

The Simulation Control settings define the overall process of the calculation as for example the timestepping interval and the maximum time you want your simulation to run before it is automatically cancelled.

### Solver¶

The described **Heat transfer** analysis of the finite element code CalculiX Crunchix (CCX) is only available
via the **solver perspective**. You may as well choose the finite element package **Code_Aster** for this analysis type
(Heat transfer CA)
using the standard **Heat transfer** analysis from the **physics perspective** or via the **solver perspective**
choosing **Code_Aster** as solver. See our Third-party software section
for further information.

See our Third-party software section for further information.