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Thread: removing gas from water

  1. #1 removing gas from water 
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    i have seen some articles about putting water in a vacuum and making it boil.

    related to this is if you put water in a sealed environment and start making a vacuum at the top you will see bubbles rise from the water - this is apparently not the water boiling but gas from the water escaping relative to the level of vacuum to be found at the top.

    My Question:

    If I was to remove gas (in this case i think it would be air) from the water with a syringe and keep the water in the enclosed environment will the water now be more dense then it was before??

    How would this effect the performance of the water if it was then used to cool an object (for the purpose of this question the object will not produce enough heat at any time to make the water boil).............would this make the water more or less efficient or have no 'real world' effect whatsoever?


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  3. #2  
    Forum Ph.D.
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    you would never notice the minute difference, besides that just heating the water will drive out the dissolved gas


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  4. #3  
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    The boiling point decreases as you reduce the pressure, so the water will boil if you draw a sufficient vacuum. Example, at 0.05 bar (0.725 psia) water boils at about 91.2 F. Density doesn't change much with pressure. It's more a function of temperature. If anything, its density would decrease with decreasing pressure, temperature remaining the same.

    http://www.efunda.com/materials/wate...mtable_sat.cfm
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  5. #4 Re: removing gas from water 
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    Quote Originally Posted by fatman57
    i have seen some articles about putting water in a vacuum and making it boil.

    related to this is if you put water in a sealed environment and start making a vacuum at the top you will see bubbles rise from the water - this is apparently not the water boiling but gas from the water escaping relative to the level of vacuum to be found at the top.

    My Question:

    If I was to remove gas (in this case i think it would be air) from the water with a syringe and keep the water in the enclosed environment will the water now be more dense then it was before??

    How would this effect the performance of the water if it was then used to cool an object (for the purpose of this question the object will not produce enough heat at any time to make the water boil).............would this make the water more or less efficient or have no 'real world' effect whatsoever?
    A couple of things happen at reduced pressure.

    One that has been mentioned is that the boiling point decreases.

    The other is that the solubility of gasses in the water decreases, which is why soda fizzes when you take off the top.

    And yes, density varies with pressure. You can try this experiment. Get a glass soda bottle. Fill it to the top with water. Get a match and break off the head. Put the head in the water and put your thumb over the mouth of the bottle. By varying the pressure with your thumb you can vary the height of the match head in the bottle.

    Degassing water would have little effect on the heat capacity and no effect on the boiling point. But you can affect the boiling point by dissolving thngs like salt in the water.
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