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Homework Help: Compressed water enthalpy

  1. Feb 18, 2010 #1
    1. The problem statement, all variables and given/known data
    Finding the enthalpy of water with the following known data:
    Water, temperature 45 degrees, pressure 1.2 bar

    2. Relevant equations
    Q' = m'(steam) * h(gas) - m'(steam) - h(fluid)

    3. The attempt at a solution
    I need to find the enthalpy of water under the circumstances above, to calculate a quantity of heat transferred by condensing steam. However I seem to be unable to find the enthalpy of the fluid. All attempts to find the enthalpy, I end up with either tables of saturated water or compressed water at pressures way above 1.2bar. Anybody can help me with the problem?
  2. jcsd
  3. Feb 18, 2010 #2
    Just look the values up in the steam tables.

    I am assuming that you are using degree C because your pressure is in bars. From my copy of the NBS/NRC Steam Tables I have the following value.

    h for compressed water is 188.51 kJ/kg @ 45 C and 1.2 bars.

    You haven't specified at quality and you clearly do not have superheated steam because the saturation temperature @ 1.2 bar is 104.81 C and you are well below that temperature. Therefore, you have a liquid-vapor mixture which means that you need a quality value in order to determine the other enthalpy value that you need.

    Do you follow?

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