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B Would this device(pic inside) work for boiling cold water?

  1. May 23, 2017 #1
    Imagine some giant glass(or other material) dome placed on top of some ocean or lake. Then pump some air out of this dome, until the water level rises a few meters under the dome.
    Place another dome below the first dome, and repeat the process, resulting in a little less pressure in the second dome.

    Keep repeating this, until the pressure in the final dome is low enough to get water boiling at room temperature.

    Would such a device work or did my thinking go wrong somewhere?

    The picture below shows how I imagined it.

  2. jcsd
  3. May 23, 2017 #2


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    Yes, but why bother with more than one dome?
  4. May 23, 2017 #3
    Because the water levels would be too high otherwise, and there would not be enough space left above the water level.
  5. May 23, 2017 #4


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    I'm not following: since the large dome covers all the little domes, you only need to pump out the large dome to the pressure where the water level reaches what you show in the pic (about 33 feet, at room temperature). No other domes needed. Are you thinking the vacuum is greater with the extra domes or something?

    What you have there is very much like a mercury barometer, just larger and using water:

  6. May 23, 2017 #5
    Yes, the vacuum should be greater at the domes inside the way I imagined it. However, if as you say, you could get a great enough vacuum to boil water at room temperatures with a tall enough dome, with enough "vacuum space" on top of the water level, then I guess only 1 dome is required for my follow up questions.
  7. May 23, 2017 #6


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    Well, ok; if the pump you are using is only capable of a progressive fraction of a vacuum (eg, 1/4 atmosphere per step would mean 4 steps), then I guess you'd need multiple domes. But any decent vacuum pump would be able to do it in one step.
    You need the single dome to be equal in height to your largest dome regardless of how many steps you use. It needs to be >33 feet.
  8. May 23, 2017 #7
    I will first state my follow up question independent of the dome, as depending on the answer to it, it might become irrelevant.

    Imagine a long cylinder with a piston. We fill the cylinder with some water. The piston is right on top of the water.

    Now we pull the piston, creating a vacuum inside the cylinder with the water inside, to the point where water would boil at room temperatures.
    This pull action will of course cost energy.

    When the water boils, it should, as I imagine it, push the piston further, without us having to put more energy in. The water basically "explodes" at this point.
    We store the energy out of this process in a flywheel or spring or whatever else is usable.

    Since, as I imagine it, energy stored in the water was lost, the steam inside the cylinder would cool down, and we would end up with colder water than initially. When it cools down, the cylinder is pulled back again, and we could again store this pull motion in a flywheel or something else.
    We are now back with water in the cylinder and the piston on top of it. The water is however colder. The difference in energy is stored in the flywheels.

    We empty the cold water and refill it with room temperature water, repeating the process.

    Where did my thinking go wrong, as this appears like we could actually use water as a fuel. Basically extracting the energy the sun puts into heating up the water. And heated water at room temperature we certainly have enough of.

    The dome would just help with not having to pull that much initially, but having water that is already close to the boiling point.
  9. May 23, 2017 #8


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    I'm not sure why you would think that last part. In order to maintain the boiling you have to maintain the vacuum. That means you need to be constantly applying a force to the cylinder (and moving it) to maintain the required vacuum pressure to make the water continue boiling. There is no energy extraction here, only continuous energy input.

    Note, this also assumes the water will absorb heat from the surroundings fast enough to remain roughly at the starting temperature. Otherwise the process slows down.
  10. May 23, 2017 #9
    The last part comes from experiments like this one

    In a vacuum water boils and turns into ice later. You end up with colder water if you somehow would extract the kinetic energy out of the steam, would you not?

    Or let me put it differently.

    If let's say our atmosphere was much thinner, to a point where water would already be boiling at room temperatures. Would we not be able to extract energy out of the steam of the boiling oceans simply by placing some turbines such that they would extract some of the kinetic energy of the steam?

    The steam in turn would have to cool down when you extract kinetic energy out of it or so it appears to me, ending up becoming water again.
    Last edited: May 23, 2017
  11. May 23, 2017 #10


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    You'd have to draw me a picture with labels because I'm not clear on what you are saying. But in the picture you drew in the first post, the height of the water is 33 feet.
    It doesn't suggest anything of the sort, since it provides no measurement of pressure and doesn't have a piston or anything else to indicate the pressure has risen once it starts boiling -- you're filling in the blanks with your imagination....

    ...but can't you hear the vacuum pump running continuously throughout the duration of the experiment? If that isn't enough for you, try putting some numbers to what you think is happening and check the actual properties of water and steam against them.
    Instead of "if you somehow", please remain focused on what you have suggested would happen and try to figure out what would actually happen. "If you somehow" is skipping steps in your own idle speculation!
    Yes! Because you didn't need a vacuum pump to create the vacuum! But for your setup, if you attach a turbine at the top, you're just using your vacuum pump to create airflow (and steam flow) to spin the turbine!
  12. May 23, 2017 #11
    So you agree that if we thinned the atmosphere of earth to the point it would resemble the dome atmosphere, we could extract energy out of this system, but for the dome you believe that we would actually have to put more energy in into maintaining the vacuum or pressure to be more precise.
    Well, maybe I am imagining something wrong but this seems a bit strange to me, as you could consider the earth itself as the dome if you were to thin earth's atmosphere enough.

    As for the piston idea I posted, you seem to be implying that the kinetic energy of the steam sources only from the energy you put into pulling the piston. So for you to understand why I was imagining that you could get the piston to move further without pulling at it anymore once the water boils, is because I was thinking that the low pressure acts similar to a catalyst, where the kinetic energy of the steam is not only stemming from the energy you put into creating the vacuum/low pressure but part of the kinetic energy being from the stored energy of the sun, hence a temperature decrease.
    Of course, if this is not the case, then what I imagine is wrong.

    Or to put it differently. I imagine the water like a spring, which the sun pushes together in a sense, storing energy in the water.
    The low pressure/vacuum is only the release mechanism of this spring, the steam's kinetic energy stemming from the release of this spring which the vacuum acted as a catalyst/release mechanism on, hence resulting in cooled down water once you take away the steam's kinetic energy.
  13. May 24, 2017 #12
    Maybe a better way to explain it by going macroscopic.

    Let's say we have a bunch of cannon balls with springs attached to them. Those cannon balls also have solar panels attached to them along with a pressure-meter.

    When the sun shines, the energy generated by the solar panels, is used to compress the springs and keep 2 cannon balls together with some kind of locking mechanism.

    The mechanism would unlock when the pressure meter registers a certain pressure level. The energy stored in the springs would translate into kinetic energy of the cannon balls.
    If we put such cannon balls inside our piston, we certainly would end up with more energy in our flywheels than we used to put in when pulling the piston to create less pressure, especially if the pressure was already close to the release pressure initially.
    Also, we wouldn't have to pull anymore, but the kinetic energy of the cannon balls once the lock is released would be enough to push the piston further.

    Hope this analogy clears up how I was imagining it, which of course might not be how it really is.
    If the experiments show different results then I guess I am wrong.
  14. May 24, 2017 #13
    This should be easy to confirm experimentally.

    Surely, if the earth's atmosphere pressure was less, such that it would be close to the boiling point of water at room temperature, it wouldn't make a difference to the experimental outcome as you describe it, I would think.

    So all we would need is a vacuum chamber "simulating" earth with a thinner atmosphere, where water at room temperature is close to the boiling point.

    Inside this chamber, we place a cylinder/piston with some water at room temperature.

    According to you, if we had a device pulling on the piston, reducing the pressure inside the cylinder to the boiling point, we would have to keep pulling still at all times if we were to prevent the piston from collapsing back.

    Should at any point in time, when the water starts boiling, the piston require no pull anymore, but instead starts pushing in the opposite direction, hence stored energy from the sun in the water be turned into kinetic energy in the steam which pushes against the piston from inside the cylinder, I would be right.

    Is anyone aware of such an experiment, possibly on video I could look at?
  15. May 24, 2017 #14
    Ok, let me step in and reformulate your idea a little and let's see what kid of answers I get.
    lets say we made that first dome, pumped out the air and created a vacuum, the water now rises a certain level and its surface boils, I imagine the vacuum wouldn't even have to be that good or if it were the boiling would be even stronger because if the dome was made from glass it would have a much higher temperature inside due to sun rays and would function like a greenhouse.
    So we have this dome and water boiling inside of it, now since water vapor or steam tends to rise upwards we could collect it at the top and turn it back (condense) to water, what we would have gained is height , we would have created a similar situation like a pump because our water would now be at a higher point, in a reservoir of sorts, we could then let it flow back down at the outside of the dome and put some water turbines in the way so that it would spin them and generate electricity.

    So what you think , would the energy created by water flowing down be more than the energy put in to create the vacuum, I think it should be because the extra heat for extra boiling would be added by the sun.
    The only question is how large of a surface area one would need for such a dome to create significant steam to have any meaningful power output from the water running down the side and turning a turbine...?
  16. May 24, 2017 #15


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    The system would reach equilibrium with an atmosphere consisting of water vapor at exactly the right pressure and temperature so that evaporation and condensation are taking place at identical rates. No boiling.
  17. May 24, 2017 #16


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    Staff: Mentor

    There are two ways to look at it:
    1. The scenario you describe would run for the planet until the oceans boiled away or reached equilibrium, just like in your vacuum jar with the pump shut off.
    2. The earth already has a thermodynamic cycle involving evaporating water, heated by the sun - it just doesn't work the way you describe.
    I'm sorry, but it isn't just wrong, it is gibberish.
    Water isn't like a spring. That's gibberish too.

    At this point, I'm going to close this idle speculation/personal theory/attempted perpetual motion machine thread.
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