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Boiling water more efficiently

  1. Sep 12, 2012 #1
    While boiling water, I was thinking: Would one liter of water boil faster or slower if I boil it all at the same time, or if I do it in stages, ie: First boil one deciliter, then add a deciliter and wait it to boil, and so on until there's one liter of boiling water.

    Stated a bit more formally: Suppose you have 1 liter of water at a certain temperature (just for the sake of example let's say 10 degrees celsius) and you have a hot plate and a pot, and you want to raise the temperature of the water to 100 degrees celsius. Two different methods are tested:

    1) Just put the 1 liter of water in the pot, and wait for it to reach 100 degrees.

    2) Add 1 dl of water to the pot, wait for it to reach 100 degrees, and repeat this 9 more times.

    Which of those methods would be faster, or does it make any difference?
     
  2. jcsd
  3. Sep 12, 2012 #2

    mathman

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    As a practical matter, it takes longer to do it in steps, because of the transitions. Ignoring that it would take the same amount of time because the heat quantity needed is the same.
     
  4. Sep 12, 2012 #3
    Doing that in steps increases the heat exchange with the environment, so not only does it take longer, it wastes more energy.
     
  5. Sep 13, 2012 #4
    Not to mention the above two answers, in the second scheme you will lose energy via surface evaporation at each stage.
     
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