Thermodynamic table help?

Just by given the information T= 110 degree celcius and P = 5081kPa and v = 0.00030437m3/kg

How do I know it is in which state like superheated vapour, saturated vapour, mixture, liquid ,compressed liquid? Any guideline is really I hoping for. Thanks

5 Answers

  • Jacob
    Lv 5
    9 years ago
    Favorite Answer

    To determine if its a superheated, compressed liquid, etc., you need to search your tables for one your properties given, in this case either pressure, temperature or specific volume. An easier way to do so is by looking at a T-v or P-v diagram but those are usually not readily available, so I'm just going to tell you by the table method.

    If you are given a temperature and a pressure (like you are in this example), you will not usually be dealing with a mixture. This is because the temperature of the substance will remain constant under the wet dome (the name for the dome shape in those diagrams) so long as the pressure is also constant as well. Because of this, you have saturation temperatures and pressures. We can still determine what state we are dealing with based on the temperature and pressure. If they equal the saturation values, we are dealing with a mixture.

    So to know what state your fluid is in this case, you are just going to look at either the pressure or temperature tables. If, using the pressure tables, the temperature is less than the saturation temperature, the substance is a compressed liquid, and if greater, it is a superheated vapor. If, using the temperature tables, the pressure is greater than the saturation pressure, the substance is a compressed liquid, and if less, it is a superheated vapor. So, in short:

    T=Tsat and P=Psat: Saturated Liquid Vapor

    T < Tsat|Pressure: Compressed Liquid

    T > Tsat|Pressure: Superheated Vapor

    P > Psat|Temperature: Compressed Liquid

    P < Psat|Temperature: Superheated Vapor(The|Pressure means to look in the pressure table at the given pressure, and|Temperature means to look in the temperature table at the given temperature)

    So, for this example, go to the pressure tables to search for 5081kPa. When you find it, look at the saturated temperature that corresponds to that pressure. If it is higher than 110C, then you are dealing with a superheated vapor. If it is lower, then its a compressed liquid.

    To further help you with other problems:

    If you are given y (any other property besides temperature and pressure: for example, specific volume, enthalpy, entropy, etc.) and another property, we can use the other property to find what y,f (saturated liquid) and y,g (saturated gas) are. If y is less than y,f then we know that we are dealing with a compressed liquid. If y is greater than y,g then the substance is a superheated vapor. If y is between y,f and y,g then the substance is a mixture.In short:

    y < y,f : Compressed Liquid

    y > y,g: Superheated Vapor

    y,f < y < y,g: Saturated Liquid Vapor

    We are given tables for properties in each of these states. If we are dealing with a mixture, the we use the saturated tables. If we aredealing with a vapor, we use the superheated tables. For a compressed liquid, however, we can either use approximations or the compressed liquid tables. Due to the lack of good compressed liquid tables,however, we typically approximate them.

    I hope this helps! The process will come second nature to you once you do it a few times. You are also going to want to memorize the equations for steam quality x:

    y = y,f (1−x) + y,g*x = y,f + (y,g − y,f)x = y,f +y,f,g*x

    where y can be any property found in the thermodynamic tables other than Pressure or temperature.

    Source(s): Mechanical Engineer
  • hamson
    Lv 4
    4 years ago

    Thermodynamics Tables

    • Commenter avatarLogin to reply the answers
  • 9 years ago

    go to the table for saturated liquid/vapor, look up that temp and see what the pressure is [which is essentially looking up the vapor pressure at that temp].

    If pressure > that given, you have a subcooled liquid, <that given means superheated vapor only; = means it could be either saturated liquid or saturated vapor or some of both both. V will resolve that.

    HOWEVER, water boils at 100C with pressure 101.3 kPa and the pressure does not go up that fast in just ten degrees, so I am pretty sure you have a liquid, and a subcooled liquid at that.

    • Commenter avatarLogin to reply the answers
  • 4 years ago

    For the best answers, search on this site

    Suppose you have a steam flow exiting a turbine and you know the temperature and enthalpy but not the pressure. Go to your steam tables, find the temperature, look in the H column until you find that H, then read the pressure. However, if that exact H is not there, find where it would be between the two values above and below it. Then figure out how far from one to the other the exact value would be. Go to the P column and move that far [proportionately] between the P values to find the interpolated P value for the exact H value.

    • Commenter avatarLogin to reply the answers
  • How do you think about the answers? You can sign in to vote the answer.
  • Anonymous
    4 years ago

    Download the software Engineering Equation Solver. It does all this for you.

    • Commenter avatarLogin to reply the answers
Still have questions? Get your answers by asking now.