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Fresh and Salt Water and Heat Transfer
Name: Kaylen L.
Status: student
Age: 13
Location: N/A
Country: N/A
Date: 1/13/2003
Question:
Why does salt water hold heat better than fresh water?
Replies:
Hello,
Here are two of possible ways of interpreting the question and the
corresponding answers.
1- For the same volume of water, one fresh, one salted, which one holds
more heat? The answer is fresh water.
Pure water has the highest specific heat (the amount of heat needed to
raise the temperature of 1 kg of a substance by 1 degree C). Addition of
salt reduces this heat storing capacity.
2- For the same volume of water, one fresh, one salted, which one boils
later (i.e., at a higher temperature), and thus can hold more heat prior
to boiling and evaporation? The answer is salt water. Adding salt to
water raises its "boiling point", which is the temperature at which it
boils. The reason for that is that salt molecules, acting like tiny
magnets, tend to hold the water molecules down. Water molecules then need
more energy (thus higher water temperature) to be able to escape (evaporate).
Ali Khounsary, Ph.D.
Argonne National Laboratory
There seems to be a myth (I think!) that salt water "holds" heat (whatever
that means.) better than fresh water. On either a mass or molar basis the
heat capacity of the two are quite similar as is their thermal conductivity.
So I ask, "Show me the data that indicates that the two have very different
thermal properties."
Vince Calder
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Update: June 2012
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