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Conduction of heat from metal to air

  1. Jan 16, 2016 #1
    A typical example is a iron chair gets cold in winters and wooden chain not. We all know iron is more conductive but how this thing possible at molecular level of conduction of heat from metal to air. In general conduction I know it is possible due to vibration transfer of molecules but how it's possible from metal to air. Please explain at molecular level.
     
  2. jcsd
  3. Jan 16, 2016 #2
    not so.

    Can you refine your question or provide the source you found this?

    PS: If you put a whole bunch of different things at room temperature in a cold refrigerator, do you think any will be colder than any other after sufficient time has passed? Some may get colder faster or slower due to conduction, convection [or radiation] but all will end up at the ambient temperature of the refrigerator, right?
     
  4. Jan 16, 2016 #3
    Okay I am taking about rate of flow of heat. And it's in time limit like we put chairs from indoor to outside for five minutes. That's what I talking about why metal gets cold faster with only contact with air.
     
  5. Jan 16, 2016 #4
    Hi,
    Conduction electrons.....loosely bound electrons.....same reason as some materials are insulators [wood] others are conductors [iron] of electricity...
    those with loosely bound electrons can diffuse more quickly carrying either heat energy of electrical energy or both from atom to atom....

    A few views:
    Electrical conductivity of non-metals is determined by the susceptibility of electrons to excitation from the valence band to conduction band.....https://en.wikipedia.org/wiki/Valence_and_conduction_bands

    https://en.wikipedia.org/wiki/Heat_transfer#Conduction
    [has a link to more details]

    http://farside.ph.utexas.edu/teaching/sm1/lectures/node86.html
     
  6. Jan 16, 2016 #5

    russ_watters

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    Staff: Mentor

    You are probably mistaking your perception of the metal chair being cold for the reality of what temperature it really is. Metal chairs both hold and transfer heat faster than wooden ones, which have a lot of air in them, which insulates them. So a metal one will transfer heat from you faster than a wooden one and because our perceptions of "cold" and "hot" are largely based on heat transfer rate, the metal chair will feel colder even if it is not.
     
  7. Jan 16, 2016 #6
    I know about general conduction but I am talking of process of transfer of heat from metal to air. How it happens at molecular level or it's just not conduction and is radiation.
     
  8. Jan 17, 2016 #7

    Svein

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    Science Advisor

    The heat transfer from <something> to air is effected through convection and radiation. However, the internal transfer of heat through a metal chair is largely due to conduction, which is much faster. Therefore, a metal chair is going to be cold all the way through faster than a wooden chair (since wood is a very bad heat conductor).
     
  9. Jan 17, 2016 #8
    When you are thinking about heat exchange due to radiation, you are thinking about significant temperature differences. In other words, any substance has to be pretty hot to lose much heat energy via radiation....an incandescent light bulb for example is pretty hot, 2,000 or more Kelvin I think. Since it's encased in a vacuum, virtually all the heat loss is radiation....and something like 97 or 98% of the power is dissipated that way. The largely infrared radiation heats the bulb of course, so it loses heat via conduction as air passes.

    See the chart here and the explanation beneath:
    https://en.wikipedia.org/wiki/Thermal_radiation
     
    Last edited: Jan 17, 2016
  10. Jan 18, 2016 #9
    Everything in universe radiates heat except those with temperature of 0kelvin.
     
  11. Jan 18, 2016 #10
    Yes, but if you have two objects (say A and B), then A radiates heat to B and B radiates heat to A. If they have the same temperature, the heat radiated equals the heat received; there is no net heat transfer between A and B. If the temperatures are "close" the net heat transfer is "negligible."

    Metal to air heat transfer is, as said above, by convection. If there is a wind, the air molecules adjacent to the metal are constantly being replenished, and thus carry heat from the warm metal. If there is no wind, the heated air expands and rises, creating its own wind so to speak.

    For normally experienced situations (like chairs on the patio) the convection is more significant than the radiation term.
     
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