Could we not do it with a radiator source? (1) Imprint the faces in DesignModeler (2) Create a Named Selection for these imprinted lines in ANSYS Meshing. (3) Find these lines in the Boundary Conditions -> Internal. (4) Select the lines and convert to Radiator type.

Laureano, is it acceptable to have the heat go on both directions or is it only on one side of the interface? Do you know the heat flux or the heat transfer coefficient? Look closer at the documentation.

Edit: Sorry I missed you said that it is 20 [W/m²]. Yes that can be done as above. Is there potentially water flowing thru this line? Or does it act like a wall? If you switch these interior to a wall then it will create it and a shadow. Then you can specify the heat transfer just in one direction, but then it restricts flow through the line.