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If you have a mixture, can you use a saturated liquid table?

  1. Sep 6, 2015 #1
    I'm working on a problem and need to find quality, mass, and pressure. I'm given a temperature (2°C), a volume (1200m^3), and a percent volume occupation (1% saturated liquid). Is it "legal" to use the saturated liquid tables, at 2°C, to find the volume or pressure (I forget which one we were discussing) and THEN move on to the correct saturated mixture table?

    Basically, given a temperature, volume, and percent volume, how would one find the quality and pressure. it's ammonia by the way, but that's not important right now. Figuring out how to find the right things is where we're at.
     
  2. jcsd
  3. Sep 6, 2015 #2

    SteamKing

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    Are there saturated mixture tables for ammonia? There aren't any for water.

    A saturated liquid implies that an equilibrium exists between the liquid phase and the vapor phase of a particular substance.

    http://seitzman.gatech.edu/classes/ae3450/phases.pdf
     
  4. Sep 6, 2015 #3
    You just answered a question I didn't realize I had. There's a Saturated Ammonia and superheated Ammonia table. So I can just interpolate my data points to fit the 2°C temperature? Essentially, since I know nothing about Ammonia, can I look up my information with JUST the temperature?
     
  5. Sep 6, 2015 #4

    SteamKing

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    You're still confused.

    Superheated vapor is just that: vapor. There's no liquid present because it's all been evaporated.

    The saturation line for a given substance is the combination of temperature and pressure where 100% vapor exists. At any point below this line, there will be a mixture of vapor and liquid, until a point is reached when only the liquid phase exists.

    If you look in the saturated liquid tables, you should find a listing of properties (specific volume, internal energy, enthalpy, entropy) for both the liquid and the vapor phases, because the saturated liquid can be a mixture of both phases. The properties of the mixture are determined by the quality of any vapor fraction present. A quality of 0% means you have only the liquid phase, and a quality of 100% means that only vapor is present. A quality figure in between 0% and 100% means that that proportion of vapor is present with the remainder being liquid.

    In the link in Post #2, from p. 7 onward, the procedure to calculate the properties of the saturated mixture is explained using the tabulated properties for ammonia, water, whatever.
     
  6. Sep 6, 2015 #5
    Sorry, it's the terminology that's different.

    I've been using compressed liquid, saturated mixtures, and superheated vapour tables, but the ammonia only has a Saturated table and Superheated table. That was the problem =\ But I think we got the appropriate interpolation now!
     
  7. Sep 6, 2015 #6

    SteamKing

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    Compressed liquid suggests there's no vapor present.
    Superheated vapor suggests there's no liquid present.

    That leaves ...
     
  8. Sep 7, 2015 #7
    For your purposes, the Saturated Table is the one to use. This table gives the pressure, temperature, and specific volumes of the liquid and vapor at equilibrium with one another. Knowing the total amount of ammonia present, the volume of the container, and the specific volumes of the liquid and vapor enables you to calculate the mass split between the liquid and the vapor.

    Chet
     
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