Reply To: Heat transfer in thin walls – Shell Conduction

[Rob]

That sounds about right - the wall and wall:shadow are the opposite "sides" of the wall, so in this case face different fluids.
Fluent creates virtual cells and then solves the conduction through and along the walls. This should be covered in the heat transfer section of the Theory Guide. Check for links in the Boundary Condition section of the User's Guide too.