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How to calculate pressure from steam

  1. Aug 25, 2015 #1
    So let's say we have a cylindrical pressure vessel of volume 2.4 x 10^-3 m^3 carrying 2 liters of water heated to 130 degrees Celsius, how would I calculate the circumferential pressure inside the container?

    radius = 56x10^-3 m
    height = 0.24 m

    I know the equation would be stress=pressure x radius / thickness. Just never had to calculate the pressure before.

    Also, if someone is feeling extra nice, would you mind clrifying this for me please: If steam is created in an environment that has 2 liters of water, but then the element further heats the water to 130 degrees Celsius, then would this create saturated steam or superheated? I always thought superheated, as the vapour must exceed 100 at some point if it is in a sealed environment. I just read something today that confused me somewhat.
     
    Last edited: Aug 25, 2015
  2. jcsd
  3. Aug 25, 2015 #2
    Is this a homework problem?
     
  4. Aug 25, 2015 #3
    You could say it is. I'm at home and working. Not a student though. Trying to design something and refresh my engineering skills.
     
  5. Aug 25, 2015 #4

    anorlunda

    Staff: Mentor

    Google online steam tables. You can look up the answer there. As long as the volume of the container is bigger than the initial volume of water, it will not influence the answer.

    As long as you have both liquid and vapor in the tank, the vapor will be saturated, and you can look up the properties of saturated steam. Is there also air in the container? If yes, it will affect the answer.

    I certainly hope that you are not trying this as a home experiment. Boiler explosions are deadly. We do not discuss dangerous topics on PF.
     
  6. Aug 25, 2015 #5
    Absolutely not something I would experiment with at home :) I've another year of design and research before I have some prototype to test, but that would be done in a controlled environment and with professionals.

    There will be air in the container, then 2 liters will enter, seal, and then heat to 130 degrees.
     
  7. Aug 25, 2015 #6

    Would you mind giving me an online link. I'm a bit confused as to what to do...
     
  8. Aug 25, 2015 #7
    Also, please tell us your understanding of the term circumferential pressure. Do you really mean "circumferential stress?" If this is what you want, then you also need to know the wall thickness of the tank.

    If there is air in the tank to start with, then you need to use the ideal gas law to include its contribution to the total pressure.

    Chet
     
  9. Aug 25, 2015 #8
    The hoop stress is what I mean. Firstly I need to understand the uniform force created by this circumstance I guess. Isn't there some simple calculator online?
     
  10. Aug 25, 2015 #9

    russ_watters

    User Avatar

    Staff: Mentor

    I don't mean to sound rude here, but you are asking some questions you could be googling. The equation for hoop stress is pretty straightforward, so I'd just use that...but does an online calculator exist? I don't know: I could Google that for you...
     
  11. Aug 25, 2015 #10
    Sorry but you are being a bit rude. I've already stated the hoop stress equation above. Coming at something from a fresh angle can be a bit too broad and makes you unsure what you should be looking at.
     
    Last edited: Aug 25, 2015
  12. Aug 25, 2015 #11
    I don't think Russ was being rude. What he was referring to was that there are two separate parts to this problem:
    • Determining the final pressure at 130 C
    • Determining the hoop stress
    Russ was saying that the equation for determining the hoop stress from the pressure is readily available on the internet. Also available on the internet is the equilibrium vapor pressure of water vapor in equilibrium with liquid water at the each temperature. Also, if you assume that the starting pressure of the air is 1 atm, and you assume that the volume of liquid water does not change significantly when the temperature goes to 130 (and some of it vaporizes into the heat space), then you can calculate the new pressure of the air using the ideal gas law. So, you have everything you need to solve your problem.

    PF rules are that we don't solve the problem for you. So please start using the info we have provided and show us your progress. If you still can't solve it with the information we have provided, you need to hire a consultant.

    Chet
     
  13. Aug 25, 2015 #12
    Okay, let's see your work. Equations and calculations. Which is it going to be....
     
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