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Evacuated Tube with Steam

  1. Apr 29, 2015 #1
    Hey everyone,

    I'm building my first evacuated tube solar oven and I seem to run into a problem I cant get around. First of all, I am going to use half inch type K copper pipes with water as a heat transfer fluid. I am putting a vacuum (100 mbar or so) on the tubes to lower the boiling point of the water. The tubes are about 10 feet long, giving me a volume of 23.56 in^2. I'm doing this in order to have the water in vapor form most of the time in order to superheat the steam and achieve temperatures higher than 212F. If my highest pressure can be 120 psi, according to Copper.org which describes pressure rating for brazed joints using saturated steam, what is the amount of water I need to add to the pipes in order not to exceed that pressure?

    Thanks in advance for your help and advice, it'll really help me out :)
     
  2. jcsd
  3. Apr 30, 2015 #2

    rbelli1

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    Gold Member

    What is the maximum temperature you are looking to operate at?

    BoB
     
  4. Apr 30, 2015 #3

    400F would be my max temperature in the heat pipes.
     
  5. May 5, 2015 #4

    rbelli1

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    Gold Member

    This http://www.slideshare.net/muhammad_anam/steam-tables
    might be helpful. I don't know how to calculate for your situation. I just know that the temperature is important.

    If you keep the vapor pressure below your 120psi then any amount of water is OK. Could you limit the temperature to 340F? If I am reading the linked tables correctly you then stay below 120psi at any volume. You would also keep a liquid phase at all times.

    BoB
     
  6. May 6, 2015 #5
    Thanks for the table BoB, they'll definitely be useful. As of know I don't have a way to limit temperatures...however i've done some more reading and know that I need to have saturated steam, not superheated steam; to capture the latent heat of water condensing.
     
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