losing patch definitions after exporting to .stl format

Hello there,

I wished to convert the generated 3d mesh into .stl format so that can work on further using cfmesh. I have defined all the patches ( airfoil, far_field ) in geo files and it works well under the visibility window, however, after I convert to .stl format and I opened it up, there is only 1 patch called " Solid Created by Gmsh ".

May i know how can i retain the patchs after exporting ? Thanks