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The properties of Superheated steam

  1. Jan 14, 2008 #1
    Looking at the steam tables I see that the entrolpy of steam at a constant temperature increases with a decrease in pressures.

    As an example, Steam at a temperature of 1000 degrees has an entrolpy 1520 @ 500 PSI.

    The same temerature steam at a pressure of 2000 PSi holds less energy, 1475.

    Can anyone explain this?
     
  2. jcsd
  3. Jan 15, 2008 #2

    Mech_Engineer

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    Wait, are you talking about enthalpy or entropy?!

    Enthalpy is a measure of internal energy, whereas entropy is not.
     
  4. Jan 15, 2008 #3
    ah good catch.

    I ment enthalpy. The numbers reflect enthalpy, but of course they both go up.
     
  5. Jan 15, 2008 #4

    Q_Goest

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    Hi millsk,
    For a thermodynamically ideal gas, the internal energy is independent of pressure. Internal energy depends on temperature only.

    For an ideal gas, PV = constant given any temperature.

    So enthalpy, which is U + PV should be constant for an ideal gas that is also thermodynamically ideal for any given temperature as pressure is varied.

    The fact enthalpy decreases slightly at higher pressure is primarily due to the way the gas molecules ‘rearrange’ themselves at the higher pressure. Note that an increase in enthalpy as you’ve noticed here is the most common deviation from ideal behavior.
     
  6. Aug 17, 2010 #5
    my question is why only super heated steam is used for steam turbines??
     
  7. Aug 22, 2010 #6
  8. Aug 25, 2010 #7
    Next about 550 MW power engine project:

    [​IMG]

    [​IMG]

    [​IMG]

    550 MW

    [​IMG]


    Regards Andrew:biggrin:
     
  9. Aug 25, 2010 #8
    i dont mean to wast space, but wow thats impressive
     
    Last edited: Aug 25, 2010
  10. Aug 25, 2010 #9

    Mech_Engineer

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    It would be more impressive if it actually worked, or at least had a working prototype to back up the "pretty pictures."
     
  11. Aug 25, 2010 #10
    "pretty picture" part "How can it be in the future (first lecture) "

    Cheaper, safer

    Regards Andrew:biggrin:

    But to count V is a need to remind myself theorem of calculus
     
    Last edited: Aug 25, 2010
  12. Aug 25, 2010 #11

    Mech_Engineer

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    Uh, what? :uhh: Talk in complete sentences please.

    My point is "pretty pictures" mean nothing as to the merits and feasability of the design. It seems to me it will have a necessarily low compression ratio, and sealing will be more difficult than on a conventional cylindrical piston.
     
  13. Aug 25, 2010 #12

    Relax, you are not in the Gallery Museum with pictures, which you describe the first impression :wink:

    It is possible to include small compromise with round sometimes.
    Invention of wheel was first ,it is closest our heart.

    [​IMG]


    Possible mutations water cooled half rotary:
    Without that leaks in driving and from deducing of water half rotate "piston" . Elastic hose only several degrees twisted.

    [​IMG]

    [​IMG]


    [​IMG]

    Do not need any oil !!

    Seal or Teflon or lubricated with diesel fuel.

    OIl = diesel fuel in this picture

    [​IMG]

    I do not have to grind any 'cylinders'

    Regards Andrew:biggrin:
     
  14. Aug 25, 2010 #13
    Do you know of a few pipes for steam 246 atmospheres and 565 degrees Celsius with an outside diameter 356 mm to the turbine, have walls of 82 mm thickness....
    And are made by drilling forgings....

    [​IMG]

    Or two small bearings .....

    Regards Andrew:smile:
     
  15. Aug 25, 2010 #14

    Mech_Engineer

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    The point is that none of your rendered pictures prove that your design is a good one. Only an engineering design study and a proof-of-concept engine can do that.

    At my work (and in engineering generally) it is common knowledge that making a "pretty picture" is easy, but doesn't mean that the results it's presenting aren't total crap. This applies to CAD design, FEA, mathematical charts, everything.
     
  16. Aug 25, 2010 #15
    Oh yes, Riccardo worked on a couple of pictures of 80 years.
    But it has a good record.
    It is in this case and probably will be similar.

    But most important is the new image.....

    Now you can work on it...

    Andrew:biggrin:
     
  17. Aug 25, 2010 #16

    Mech_Engineer

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    It's like arguing with a brick wall... a brick wall that only talks in sentence fragments!

    Let me ask you this- what's your engine's compression ratio? What will its volumetric flow rate be?
     
  18. Aug 25, 2010 #17
    No, no arguing , it does have a friendly discussion to a new understanding of

    With "cylinder" and popped...

    [​IMG]

    Mutations "Long Cylinder" and 8 valve in one "cylinder"

    [​IMG]

    Are You know engine named Twin Feliks ?

    [​IMG]

    Andrew:biggrin:
     
  19. Aug 25, 2010 #18

    Mech_Engineer

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    You haven't answered my question yet- what's the engine's compression ratio?
     
  20. Aug 25, 2010 #19
    As an engineer, mechanic, you should give in the question whether it still regards to you, an engine with an electric ignition, or the engine ignition diesel.
    Because these are very different values.

    Andrew:biggrin:
     
  21. Aug 25, 2010 #20

    Mech_Engineer

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    :rolleyes:

    How about both. The point I'm making is you don't have it.
     
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