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High Temperature Situation

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  • High Temperature Situation

    Hello all. Hypothetical scenario.
    I have a cylinder 6 feet tall. 2 feet dia.
    An electrical immersion heater is fitted in the top of a cylinder with the fail safe disabled. This is placed 2 feet from the top of the cylinder.
    The cylinder has a manual vent at the top to aid venting the air after filling with water and is then shut tight.
    Their is a cold feed at the bottom of the upright cylinder feeding water via gravity from a cold cistern placed 10 feet above.
    The immersion is energised indefinately with the fail safe disabled.

    What happens next ??.
    Many Thanks.

  • #2
    Re: High Temperature Situation

    Here's what I see happening:

    There is no flow (line from cistern is dead-ended into the tank) so the water in the tank will be heated and a steam bubble will be created in the top of the vessel above the heating element. This steam bubble will be under approx 5 PSI pressure exerted by the head of water (assuming the 10 ft. height difference is measured from the top of the vessel to the water line in the cistern.

    As the steam bubble grows (and pressure with it) it will force water back out of the vessel toward the cistern. When the bubble grows to where the heating element is uncovered (no longer immersed in water) there will be no heat sink for the heating element and it will most likely burn out if the reduced heating efficiency does not let the temperature drop and the steam bubble collapse thereby covering the element again and repeating the process.
    "When we build let us think we build forever. Let it not be for present delight nor for present use alone. Let it be such work that our descendants will thank us for, and let us think, as we lay stone upon stone, that a time is to come when these stones will be held sacred because our hands have touched them, and that men will say, as they look upon the labor and wrought substance of them, "See! This our fathers did for us."
    John Ruskin (1819 - 1900)


    • #3
      Re: High Temperature Situation

      Thanks for the reply.
      If a vent is fitted to this set up will any hot water go back up the cold feed ??.