Help with Thermal Conductivity - Water vs. Air

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Discussion Overview

The discussion centers around the thermal conductivity of water compared to air, exploring both theoretical and experimental perspectives. Participants seek to clarify which substance has higher heat conductivity and the reasoning behind it, while also addressing the need for proof or derivation of the answer.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Quan Chi asks which has higher heat conductivity, water or air, and requests proof.
  • One participant suggests looking up the information and questions the necessity of a proof, implying that experimental results might suffice.
  • Another participant expresses frustration at the lack of clear information available online and shares their belief that water is the correct answer, seeking help to prove it to friends.
  • A link to a Wikipedia page listing thermal conductivities is provided, confirming that water is the correct answer.
  • A later reply introduces the idea that thermal conductivity data may not account for density differences, mentioning the Prandtl number as a relevant factor for comparison between air and water.
  • Another participant proposes that water's higher density allows for more effective heat transfer due to closer molecular proximity, suggesting a conceptual explanation rather than a formal proof.

Areas of Agreement / Disagreement

Participants generally agree that water has higher thermal conductivity than air, but there is disagreement on the necessity and form of proof required to support this claim. The discussion also highlights differing views on the role of density and viscosity in thermal conductivity.

Contextual Notes

Some participants note the importance of considering factors like density and viscosity when discussing thermal conductivity, indicating that the comparison may depend on specific definitions and contexts.

quanchi
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Help!

Which has higher heat conductivity: water or air?

And could you give me a proof as well?

Regards,
Quan Chi
 
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quanchi said:
Which has higher heat conductivity: water or air?

Have you tried looking it up?

quanchi said:
And could you give me a proof as well?


Proof? Wouldn't this be an experimental result? Granted, it is probably possible for someone to use theoretical physics arguments to predict what the heat conductivity of a substance depends upon and therefore which one would be higher. But that would be a lot of work and would seem to be unecessary if you just want the answer.

EDIT: Unless somebody has asked YOU to provide such a derivation, in which case asking somebody else to do it for you is cheating.
 
Just an answer would be enough. I have tried looking it up without success so I thought I might just ask some professional help. I have no time to do a research and english is not my native language.
And the reason I am asking this question is a quarrel I had with my friends. I thought the correct answer was water but I could not prove it to them so easily.
 
Thank you very much :)
 
Just to throw a wrench in the works, the data is not corrected for density. For example, there are two ways to quantify viscosity- kinematic and dynamic- water and air have about the same dynamic viscosities.

The Prandtl number (ratio of viscous to thermal diffusion) does take this into account, and is about 0.7 for air and 7 for water.
 
If I were to explain why water is a better thermal conductor than air, I would say because liquid are denser than air (molecular distances are small) thus giving water more opportunity to contact with the heat source.

There are rarely proofs in physics theories, if any. But explanation like those can be taken as self-evident. And in some other cases, we can only feel confident about an explanation because it's grounded on suggestive evidence and logic that's been rigorously examined.
 
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