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Homework Help: Intro Thermodynamics Question using Steam Tables

  1. Jun 19, 2011 #1
    1. The problem statement, all variables and given/known data

    A transparent rigid container is filled with 2 gallons of water. Initially the pressure is
    measured to be 10.2 psig, using a gage attached to the container. The local atmospheric pressure is 14.8 psia. It is observed that the liquid water in the container occupies two percent of the container volume. The water in the container is heated. Determine the reading on the pressure gage in psig when all the liquid has just turned to vapor (all saturated vapor). Show this process on a sketch of a T-v diagram.

    2. Relevant equations

    Equatin for quality: v = vf + x(fg)

    3. The attempt at a solution

    I understand the concept of steam tables. And I understand exactly what this looks like on a T-v diagram. I guess I am getting too bogged down in the information given to not know what to consult the steam tables for.

    I understand that the absolute pressure in the container before being heated is 25 psia, so I can get a saturated temperature reading from that, and a specific volume based on the fact the 98% of the water is steam (see above equation). But I'm not sure how to related that to the container once it's been heated. The volume stays constant and I'm left with saturated vapor, but what does that mean for the pressure?

    Any help is appreciated and I'll be happy to clear up any blurry areas of my question.
    Last edited: Jun 19, 2011
  2. jcsd
  3. Jun 21, 2011 #2
    Condition 1: P1=25psia. T1:240 F, V1=.8 ft^3/Lb, X=4.8%

    Condition 2: V2=.8 ft^3/lb, x=100% because you are saturated vapor, Vg=V2=.8 ft^3/lb

    look on steam tables at Vg= .8 ft^3/lb to find P2 and T2
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