In my admittedly naive understanding of the rankine cycle, steam is condensed back into water after passing through the turbine. Why not reuse the steam instead? It would seem to require less effort to reuse heated steam than to intentionally condense the water only to reheat it once again.

I'm sure i'm misunderstanding something about the process. Why do we have to condense the water at all?

  • $\begingroup$ Because more kinetic energy comes from the phase change I believe $\endgroup$ Commented Sep 5, 2015 at 1:16

1 Answer 1


It's for almost the same reason as my answer to your other question on the Rankine cycle: The work output of the cycle increases as the integral (area) of the P-V diagram (or T-S) diagram is increased. Condensing the steam to liquid water results in a huge change in specific volume, which makes the integral of the P-V diagram much larger than if no phase change occured.

It does seem like energy is being wasted in the condensation process, but think of how much energy it would take to compress the working fluid to the boiler inlet pressure if it were a gas. (It would be much more energy than if we just had to pump a liquid to the same pressure).

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    $\begingroup$ So steam is condensed till its heat content falls below steam's latent heat so it can be pumped back to boiler without effort of compressing steam to boiler ? $\endgroup$
    – Fennekin
    Commented Sep 5, 2015 at 10:32
  • $\begingroup$ Exactly. Compressing a vapor takes a lot more energy than compressing a liquid. $\endgroup$
    – Carlton
    Commented Sep 5, 2015 at 13:24

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