Posted 20 December 2011 - 01:08 AM
This is an appropriate question for the mechanical thread as it pertains to thermodynamics. A good visual for the steam tables is the Mollier diagram (make sure you aren't looking at the T-S diagram). On the Mollier diagram you'll see a line indicated as the saturation line, this is the dividing line between the saturated steam and the super heated steam regions and respective tables. You can see the maximum Enthalpy for saturated steam (under the saturation dome) on the diagram matches the data in the tables. This visual is useful for "seeing" what happens as steam moves from one stage to another in a thermodynamic cycle. To answer your question: It decreases in the left hand region of the Mollier, after the peak, because this is the nature of steam (if kept at saturation) and the first law. Remember h = u + Pv
The T-S diagram is more useful (IMO) but harder to read if you're not as familiar.