FreeCAD FEM Thermal Heat Transfer Simulation Guide

Setting up a thermal heat transfer simulation in FreeCAD requires using the Finite Element Method (FEM) workbench paired with the default CalculiX solver. This guide covers the complete workflow for conducting steady-state and transient thermal analyses, from preparing your solid geometry and defining material thermal conductivity to applying thermal boundary conditions, generating a suitable mesh, running the solver, and visualizing the resulting temperature distribution and heat flux.

1. Prepare the Geometry

  1. Switch to the Part or Part Design workbench and create or import your 3D solid model.
  2. Ensure the geometry is a clean, single solid object. If using multiple intersecting parts, fuse them using a Boolean Union or a Compound to ensure continuous thermal conduction across interfaces.

2. Create the FEM Analysis Container

  1. Switch to the FEM Workbench using the workbench selector.
  2. Click on the Analysis container button (yellow folder icon labeled "A") in the toolbar.
  3. This adds an Analysis container to your model tree, along with a default CalculiX solver object (SolverCcxTools).

3. Assign Material Properties

  1. Select your solid object in the tree view.
  2. Click the FEM material for solid button in the toolbar.
  3. Choose a predefined material (such as Aluminum or Steel) from the drop-down menu, or input custom values.
  4. Verify that thermal properties are defined:
    • Thermal Conductivity (\(k\)): Required for all thermal analyses (measured in \(\text{W/m}\cdot\text{K}\)).
    • Specific Heat (\(c\)): Required if you are running a transient (time-dependent) analysis (\(\text{J/kg}\cdot\text{K}\)).
    • Density (\(\rho\)): Required for transient analysis (\(\text{kg/m}^3\)).
  5. Click OK to assign the material to the geometry.

4. Apply Boundary Conditions

A thermal simulation requires defined constraints to calculate heat transfer:

  • Fixed Temperature: Select the Constraint temperature tool. Pick the faces, edges, or vertices that have a known, constant temperature, enter the value in Kelvin or Celsius, and click OK.
  • Heat Flux: Select the Constraint heat flux tool to specify a known heat load per unit area (\(\text{W/m}^2\)) on selected surfaces, or define a convective film coefficient to simulate heat dissipation into surrounding air.
  • Initial Temperature (Transient Only): If running a time-dependent simulation, apply an Initial temperature constraint to define the starting temperature of the entire body.

5. Generate the FEM Mesh

  1. Select the solid geometry in the tree.
  2. Choose either Netgen or Gmsh from the toolbar to generate the finite element mesh.
  3. Set the Max element size based on the level of detail required. Use a finer mesh near sharp corners or regions with high temperature gradients.
  4. Click Apply to generate the mesh, inspect it for quality, and click OK.

6. Configure the Solver and Run

  1. Double-click the SolverCcxTools object inside the Analysis container.
  2. In the properties panel, change the Analysis type from Static to Frequency/Thermal or Steady state heat transfer (or Transient heat transfer if modeling time-dependent cooling/heating).
  3. In the task panel, click Write .inp file to generate the input deck for CalculiX.
  4. Click Run CalculiX. Monitor the status window until the solver displays a successful completion message.

7. Post-Process the Results

  1. Once the simulation finishes, a CCX_Results object will appear inside the Analysis container.
  2. Double-click the results object to open the post-processing panel.
  3. Under the display options, change the field to Temperature or Heat Flux to view the color-coded contour map across the mesh.
  4. Adjust visibility and scale ranges to identify hot spots, thermal gradients, and rate of dissipation across your model.