water does indeed migrate through the porous terracotta clay of the carafe where it evaporates, cooling the outer surface of the pot which in turn allows heat to flow by conduction from the inside of the carafe.
Ha! An epiphany... as TigerJimmy said (and failed to register with me) the water evaporates
inside the carafe (that's the partial pressure bit) absorbing the heat of vaporization and cooling the interior, and the water
vapor is what migrates through the terracotta.
It takes me a while, but sometimes I get there... eventually.
tanstaafl.
I don't think it matters where the evaporation takes place - whether inside at the water/air boundary, on the outside surface of the jug, or somewhere within the jug wall itself. Regardless, heat is removed from the water in the evaporation process. If it's within or on the outside surface of the jug, the evaporation will cool the jug, and heat from the water will move into the jug. If it's at the water surface with the inside air, the water would cool, and absorb some heat from the jug.
If it works with the jug completely full, I suspect it's water going through the walls of the jug, as the air space would be minimal and reach 100% saturation relatively quickly. (Again, thermo was a long time ago!)
-jk
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