Thermal Dynamics Conduction Comparison

Question

I didn't have to take much physics for my advanced college degree, so I apologize if my question is painful.

From reading and experience it seems that water is a better thermal conductor than air. I wish to verify this as well as know how water compares against: alloys, pure metals, and oil.

If my question is too general, please school me on what additional knowledge I should know to ask a better question. :)

Edit:

So doing some searching, I found http://www.coolmagnetman.com/magcondb.htm which gives a good break down of resistance of different metals. This lead me to some googling, which lead me to wikipedia's http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

The wiki looks to mention the water's resistance depends on the amount of salt, which makes sense, as I believe salt is an electrolyte. The wiki also has a reference of "drinking water" which is compared to the other types. It clearly looks to be that metal conducts better. From https://van.physics.illinois.edu/qa/listing.php?id=1854 it looks like pure metals conduct better than alloys. I'm still not sure how oils fit in the comparisons though.

Answer 1

Be careful not to become confused between two distinct but somewhat similar concepts: thermal conductivity and specific heat.

Conductivity is the ability of a material to transfer heat. That is, if you had a long tube made of a given material, conductivity explains the rate at which heat would flow from one end to the other.

Specific heat, on the other hand, describes the amount of heat required to increase the temperature of an object. A material with a high specific heat requires a lot of energy transfer to change the temperature even a small amount, whereas a material with a low specific heat requires little energy transfer to change the temperature the same amount. For example, metals have low specific heats, since they heat up and cool down quickly. On the other hand, water has a very high specific heat, which is (partially) why water on a beach is still cold, even on a hot day.

Air is a very poor conductor, having a thermal conductivity of 0.024 W/m K. Water is a slightly better conductor, with a conductivity of 0.58 W/m K. However, metals conduct much more than either of these two materials - for example, aluminum's conductivity is 205 W/m K. which is over 350 times that of water. (Source: http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html)

The specific heat values are radically different. Air has a specific heat of approximately 1 J/g K, while water is at 4.186 J/g K, and metals are usually around 0.2 J/g K. That is, metals change temperature very significantly for a given heat input and water changes temperature very little, with air somewhere in between.

Electrical conductivity is not very closely related to thermal conductivity (although for metals, there is the Wiedemann–Franz law), so if you're seeking information on thermal conductivity only, make sure you don't confuse it with electrical conductivity. If you want more guidance, reply to this post in a comment, and we'll help you out.