Prepare stl file with separated surface parts for snappyHexMesh

One of the way to get a stl file with separated surface parts:
1. Create geometry using Freecad and exported as stl file;
2. Import the stl file to EnGrid, define surfaces, view the boundary code by name, then save each surface as a vtu file;
3. Open each vtu file to EnGrid, then export this face to stl file;
4. Edit the title of the stl files (all the separated surfaces), then combine the stl files to a single stl;
5. Employ snappyHexMesh to create the grid.

An alternative way is to use Blender to create the geometry, then open in EnGrid, then follow the step 2~5 as above