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Conduction (the very basics)

  1. Sep 4, 2015 #1
    From gcsescience.com;

    "Heat can be transferred by conduction only in solids."

    Q. Doesn't conduction take place directly prior to convection (when a radiator heats up a room)? If my cold hand came into contact with the warm radiator this would cause conduction; why isn't it the same for the cold air coming into contact with the warm radiator?

    Q. Is it the case that 'radiator' isn't the most sensible term for the heating device in question given that, although it does radiate heat, it mainly heats up the room by causing convection?
     
  2. jcsd
  3. Sep 4, 2015 #2

    Bandersnatch

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    Yes, there is conduction in liquids and gasses (together known as fluids). It is not very efficient though. If you can engineer your system to prevent fluid circulation (think: layers of clothing, diving wetsuits), you end up with heat transfer only through radiation and conduction.
    There's a bit more on that here and on the following page:
    http://www.spaceflight.esa.int/impress/text/education/Heat Transfer/Conduction 01.html

    The site you refer to appears to be using the simplifying approach of 'if it's small, ignore it completely'.
    It's not the best approach, IMO, as it prevents one from seeing the actual physics (like how you've observed with the radiator), and seems to be geared for drilling in answers to exam questions rather than teaching physics.
    Looking at your other threads, the site likes to speak authoritatively in that manner. Perhaps you'd be better off with a different resource for learning physics. You may still want to use that site in order to know what sort of answers the exams might expect, though.

    Yeah, 'radiator' does not predominantly radiate. I think the name comes from the common-sense observation that 'heat radiates outward from it', rather than the actual physics of heating.
     
  4. Sep 4, 2015 #3
    “If you can engineer your system to prevent fluid circulation (think: layers of clothing, diving wetsuits), you end up with heat transfer only through radiation and conduction.”

    Q. So the warm air trapped between the layers conducts and radiates heat to the layer beneath and above?

    “Perhaps you'd be better off with a different resource for learning physics. You may still want to use that site in order to know what sort of answers the exams might expect, though.”

    Yes, thanks, I’m considering this already.


    “Yeah, 'radiator' does not predominantly radiate.”


    So there is conduction (but a small amount) between the surface of the radiator and the molecules of air coming into contact with it? What predominately heats the air to start it rising, ie, starts the convection process; radiation or conduction?
     
  5. Sep 4, 2015 #4
    It may heat the room by convection but it heats the persons in front of it mainly by radiation.
    They are pretty bad at heating the room unless they are combined with a fan to circulate the air.
    And then, the layer of air right next to the hot element is heated by conduction.

    Maybe these statements are useful by making you think about their validity but you should not take them too seriously, especially if they are just about words.
     
  6. Sep 4, 2015 #5
    BBC Bitesize is usually quite good at avoiding over-complication without simply ignoring reality: http://www.bbc.co.uk/bitesize/standard/physics/energy_matters/heat_in_the_home/revision/1/ "Conduction of heat energy takes place mainly in solids... In liquids and gases (fluids) heat energy is transferred mainly by a process called convection."
     
  7. Sep 4, 2015 #6


    This is not correct.

    Chet
     
  8. Sep 4, 2015 #7

    Drakkith

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    Staff: Mentor

    Based on what you've posted from this site so far, I'd suggest that you stop using it. :-p
     
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