Converting Latent Heat to Velocity

Reducing steam pressure from 400 psi down to 100 psi in an isoentro-pic manner, as shown in Fig. 20.2, will have two positive results  

But suppose I don t wish to use the 100-psi steam and would simply like to exhaust the steam to the atmosphere. Then, instead of the steam velocity being 100 ft/sec, it might exhaust from the discharge nozzle at 500 ft/sec. Where does all that extra kinetic energy come from  

We can extrapolate this concept further. Suppose I exhaust the steam to a vacuum of perhaps 25 inches of mercury (30 inches being a perfect vacuum). Now about 15 percent of the steam would be condensed and the steam (plus condensate) velocity might be 1000 ft/sec. 1 can extract much more work from each pound of steam. Of course, not only don t 1 have any useful steam left over, but 1 also have the expense of condensing the exhaust steam under vacuum conditions (see the MoUier diagram in Fig. 20.1). 

It s Hke the girl you have taken out to dinner asking, What do you like for breakfast Just coffee, or toast and eggs  

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