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Does hot oil cool off faster than water and why?
Centreville, Va, USA
I'm not sure of the answer to that question. Let's say that you had the
same amount of oil and water, in the same size pot and at the same
starting temperature. Both will cool off by thermal conduction through
the pot. The rate of heat flow will be determined by the thermal
conductance of the pot and the temperature difference between the
liquid and the surrounding. Since the water has a higher specific heat
than most oils, it would have to lose more heat to cool down, and you
would then expect it to cool slower. However, there are other
complications. The water is also losing heat by evaporation, as
described in one of our answers on "evaporative cooling". The oils
probably will evaporate much more slowly. Also, the rate at which heat
gets from inside the liquid to the surfaces depends on whether there's
much convection (liquid circulation driven by the temperature
differences). That depends on the thermal expansion of the different
liquids, and on their viscosity- how hard it is for them to flow. All
these factors, and also how important each factor is, depend on
temperature and on the type of oil. So you can see why I don't know the
answer. But if I had to guess, I'd guess that thanks to the evaporative
cooling, a pot of really hot water would cool faster than a similar pot
of equally hot oil.
(published on 10/22/2007)
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