Confusion: outer tube heated vs. inner tube heated

[maistral]

Hi, I'm rather confused with the wording in Perry's Chemical Engineers' Handbook regarding "outer tube heated" and "inner tube heated" in double-pipe heat exchangers. Obviously both are opposites of each other, so I'd like to ask using "outer tube heated" as reference.

When we say "outer tube heated", does it mean:

- The outer tube contains hot fluid, therefore, the inner tube contains the colder fluid; or:
- The outer fluid is literally being heated, therefore it is the cold fluid, and that the inner tube contains the hot fluid?

 

[Lnewqban]

I understand it as the second option.
"Heated" means the flow is increasing its temperature between inlet and outlet.
Most of the double pipe heat exchangers that I have seen work that way:
The hotter substance flows through the inner tube, while the outer shell contains the colder fluid.