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If we were to assume room temperature of 20C, which of the fluids conducts heat better, and why?

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Water. By a lot. – Brandon Enright Jan 30 '14 at 7:06
Which of the fluids? Do you assume pressure high enough for air to be fluid in 20C? – Andrey Regentov Jun 17 '15 at 9:33
up vote 2 down vote accepted

Clicking on the first link in a quick google search for thermal conductivity of common materials takes you to the engineering toolbox. There you will find that the thermal conductivity of air is $0.024\frac{W}{m K}$ and that the thermal conductivity of water is $0.58\frac{W}{m K}$. So, water conducts heat more than twenty times as well as air.

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Just to add to this, in general, liquids virtually always conduct heat better than gases, primarily because they have higher densities. – DumpsterDoofus Jan 30 '14 at 3:06
Not just twice as well, but more than twenty times better. – Hans-Peter E. Kristiansen Jan 30 '14 at 3:16
@Hans-PeterE.Kristiansen Oops. Corrected. – Chris Mueller Jan 30 '14 at 3:20
@DumpsterDoofus -What is the relation between density of a substance and its thermal conductivity? – SRS Mar 4 '14 at 17:41
@Roopam: For fluids (such as air or water), higher density typically means higher volumetric heat capacity, which typically means higher heat transfer per volume of fluid convected across the object surface. – DumpsterDoofus Mar 4 '14 at 17:46

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