I'm having a bit of difficulty conceptually understanding a problem. Hoping someone here can clear it up for me. In a simple circular condenser tube (which is cooled by water or air) what happens the tube wall temperature as the steam inside is condensed? Intuitively I would have thought that as the steam is condensed inside the tube to form liquid condensate, the tube wall temperature would decrease along the length of the tube (from inlet to outlet) as the condensate film becomes thicker as more steam is condensed. Does that make sense? Or is the wall temperature governed by the cooling medium on the tube exterior and thus, remains constant along the length of the tube as dictated by the cooling medium - implying that it is independent of the condensate film thickness? I know that the condensate film acts as a barrier to heat transfer and thus, is a thermal resistance but I am just trying to understand what happens to the wall temperature as a result of this. I suppose that the steam temperature remains relatively constant along the tube length (isothermal heat transfer for condensation) For the thermal resistance to increase along the length (due to the film), a temperature difference must be present and this must increase along the length. For the temperature difference (ΔT=Tsteam-Twall) to increase, the wall temperature must then decrease (as the steam temp remains constant). Maybe I've answered my own question! But I would be interested to hear any other ideas on the matter.