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Homework Help: Finding the internal energy using a steam table

  1. May 7, 2015 #1
    1. The problem statement, all variables and given/known data
    What is entropy of water at 5 Bar and an internal energy of 2724 kJkg-1?

    3. The attempt at a solution
    I have looked at the steam tables, i found where the pressure is 500kpa, then i do not know where to go from there.

    Thank You
    Last edited: May 7, 2015
  2. jcsd
  3. May 7, 2015 #2


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    Gold Member

    So you will be supplied with tables that no one has told you how to use? Really?
  4. May 7, 2015 #3
    i have changed the question around
    Last edited: May 7, 2015
  5. May 7, 2015 #4
    sorry for double post, i pressed something wrong by accident.
    Last edited: May 7, 2015
  6. May 7, 2015 #5
    Let me understand correctly. You have steam tables, and you know that you have water at 5 bars with an internal energy of 2724 kJ/kg, and you are asked to determine its entropy. Is that right?

  7. May 7, 2015 #6
    Yes, thats exactly what i'm trying to do, i didnt know how to change the title and i didnt want to start a new thread.
    Last edited: May 7, 2015
  8. May 7, 2015 #7
    You found a place in the tables where the pressure is 500 kPa. What is the heading on the top of the page (e.g., saturated steam or superheated steam)?

  9. May 7, 2015 #8
    Superheated Steam
  10. May 7, 2015 #9
    OK. Now there are columns of numbers on the page. What are the headings on the columns of numbers?

  11. May 7, 2015 #10
    They are all temperatures from 100°c to 700°c
  12. May 7, 2015 #11
    What are the headings on the other columns (or rows?)?

  13. May 7, 2015 #12
    there is t(sat), then h and s for all the temperatures above. also hg and sg for saturation
  14. May 7, 2015 #13
    I thought you said that the part of the table you were open to was for superheated steam. This table is for saturated steam. What gives?

  15. May 7, 2015 #14
    i have two tables and i didn't notice, i have one with h and s, another with u and v, i just realized that i have to find the value for temperature in the u and v table using internal energy, then use that temperature to find the value of entropy in the h and s table. I got the value of entropy to be 7.272.

    Thank you very much!!!
  16. May 7, 2015 #15
    Sounds about right.

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