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Water density / volume

  1. Nov 10, 2014 #1
    Water density at 0 C is 990 kg/m3.
    Water density at 100 C is 1030 kg/m3 - 1 m3 of water "loses" about 4 % of its mass.
    Water expansion rate is 1.0002 for each 1 C increase in temperature - 2 % for the above rise from 0 C to 100 C..
    How comes that water density decreases 4 % but its volume increases just 2 % ?
     
  2. jcsd
  3. Nov 10, 2014 #2

    DrClaude

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    Staff: Mentor

  4. Nov 10, 2014 #3

    SteamKing

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    It's one consequence of dealing with too little information. The density-temperature relation for liquid water between 0 C and 100 C is a curve, with the maximum density occurring at about 4 C. Plot the values from the density table referenced by DrClaude.
     
  5. Nov 11, 2014 #4
    I mistakenly put it otherwise so, more precisely - according to the reference - it should be :
    0.999808 at 0 °C
    0.958593 at 100 °C - about 4 % of the initial value
    But the volume will increase just 2 %
    Maybe there is square root relation ?
     
  6. Nov 11, 2014 #5

    russ_watters

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    Again: the relationship isn't linear.
     
  7. Nov 11, 2014 #6
    Let it be it, but I refer to the exactly 2 points (on the "curve") between which there is the 4% decrease in density for, as it seems, 2% increase in volume
    Square root ?
     
  8. Nov 11, 2014 #7

    DrClaude

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    But as Russ said, the relationship is not linear. In other words, you can't use the same expansion coefficient at all temperatures.

    This is only true around 20°C.
     
  9. Nov 11, 2014 #8

    russ_watters

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    Please have a look at the link DrClaude gave you in post #2. You may even try dropping the data into a spreadsheet and calculating the coefficient at different temperatures. You will find that it varies substantially from 2%.
     
    Last edited: Nov 11, 2014
  10. Nov 12, 2014 #9
    But will % of expansion = % of decrease in density ?
     
  11. Nov 12, 2014 #10
    The product of density and specific volume is 1. So there is no square root relation involved.

    Chet
     
  12. Nov 13, 2014 #11
    Thank you.
     
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