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Q & A: How fast does oil cool down

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Most recent answer: 10/22/2007
Does hot oil cool off faster than water and why?
- Steve
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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