On Jul 24, 6:38*am, "Roger Traviss"
wrote:
Enthalpy change from superheated steam at 10bar/500C to saturated
water at 1bar/100C: 3052.1 - 417.5 = 2634.6 kJ/kg.

Enthalpy change from superheated steam at 10bar/500C to saturated
water at 0.05bar/32.9C: 3052.1 - 137.8 = 2914.3 kJ/kg.

Extra enthalpy available: 2914.3 - 2634.6 = 279.7 kJ/kg ~ 10%.

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Huh? *Wot's that in English then?

Too complicated to explain in a throwaway usenet post, sorry.

It's also wrong to use these simplistic enthalpy calculations to
explain engine efficiency, especially the importance of condensers.
Improvements to the low end of the cycle that appear to be unimportant
from a simple linear calculation actually turn out to be very
important when you integrate over the cycle. This is why stationary
engines, and marine engines, and especially turbines, all make the
effort to run condensers.

This is overlooked for locomotive practice - probably because the size
& weight of condensers would be so impractical anyway. I know of no
English language descriptions of steam locomotive performance that
explain this properly, or give it the due importance. The only real
treatments of it are by Chapelon and Porta. If you want such an
explanation (like I said, I don't have time to write it) you'll
probably find it best explained by a good book on beam engines and
especially something heavily theoretical on the Cornish engine (which
isn't just an engine in Cornwall).