Re: Water is the best conductor of Heat.

The question:

Conduction is the mode of transfer of heat.Transfer means both absorption and emission.When water is kept in a metal vessel,and metal vessel kept on the stove to heat it,then water in the metal vessel absorbs the heat from the metal vessel to raise the temperature.Here water molecules in that container absorbs heat from the molecules of metal vessel through conduction.Because metal cannot convect heat.Therefore water absorbs heat through conduction and transmits heat through convection.

My View:- Therefore according to me ,water is a good conductor of heat for the mode of absorption and bad conductor of heat for the mode of emission.

Question:- So, do you think my views are correct? if not suggest me with suggestions.

Hello Harshith,

I would agree with your view that “water is a good conductor of heat for the mode of absorption”, but disagree that it is a “bad conductor of heat for emission”.

In the example that you give of water heating in a metal vessel, there are a lot of complex things going on. These “things” change a lot as the temperature of the water increases.

Let’s look at your example over time: AT THE START, WHEN THE WATER IS NEAR ROOM TEMPERATURE: The heat from the stove transfers by conduction through the metal vessel, and by conduction and convection into the water. At this point, almost no heat is being transferred, or emitted from the water to the air. Where is the heat going? It is going directly into the water and raising its temperature.

A FEW MINUTES LATER THE WATER IS GETTING HOT TO THE TOUCH, SAY ABOUT 60° C: At this point, almost the same amount of heat is being transferred through the metal to the water. But now, some heat is leaving the water, being transferred to the air, mostly by convection. As the water gets hotter, it causes more and more ‘natural convection’ of the air near the pot. “Natural convection” is the process where the air is forced to circulate due to changes in temperature. As the air next to the hot water’s surface heats, it expands and its density decreases. This causes it to “float” upward in the surrounding cooler air. This causes a moving current of air to ‘convect’ the heat away from the water.

At this time, much more of the heat from the stove is still going into the water compared to the heat transferred out by the water. So the water temperature is still increasing.

FINALLY, AT THE TIME WHEN THE WATER IS AT A FULL BOIL: At this point, almost the same amount of heat is going into the water from the pot, but the temperature is no longer rising. At this time, ALL of the heat going into the water is being transferred out. The heat is being transferred out in several ways: The greatest heat transfer is due to the molecules of water leaving the vessel in the form of vapor, or steam. The vapor molecules carry away much more energy (heat) than the remaining molecules in liquid state. In addition, the escaping steam creates a huge increase in the natural convection of the air near the pot which convects away still more heat.

At this final stage, where the water is at a full boil, the heat will transfer from the water to the air at a rate always equal to the input heat from the stove. More input heat will increase the boil rate and transfer more heat to the air.

I think that you can see now that water is a very good conductor of heat!

Best Regards,

Jay Shapiro