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Two objects in a shaded positio

  1. Oct 6, 2009 #1

    GIW

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    Two objects in a shaded position.

    One white, the other black in colour.

    Both having the same mass / volume (density)

    Ambient temperature hotter on the outside of the object.

    Is there any logic to suggest the darker object will be hotter than the lighter one?

    Thanks. Gary
     
  2. jcsd
  3. Oct 7, 2009 #2
    Re: ThermoDynamics

    Yes, it may have had an initial higher temperature :)
    There may be wind, the black is more exposed, so warms faster
    There is other radiation besides the sun; the 2 radiate to each other, and black is more affected (I suppose this would tend toward equilibrium)
    Radiation from the sky-if the sky/cloud temperature is warmer than the object.
     
  4. Oct 7, 2009 #3

    GIW

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    Re: ThermoDynamics

    So if i am understanding you correctly, indirect sun will heat up the black object faster than the white one?
     
  5. Oct 7, 2009 #4
    Re: ThermoDynamics

    Yes; as I recall the radiation heat transfer is a function of (T14-T24) and the radiation coefficient (don't recall the term), 1.0 for black body.
     
  6. Oct 7, 2009 #5
    Re: ThermoDynamics

    Emissivity.

    If you are assuming steady state equilibrium, no they should be the same temperature. If you are assuming transient, then the surface of the darker colored object will have a greater heat flux on its surface.
     
  7. Oct 7, 2009 #6

    minger

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    Re: ThermoDynamics

    To Carl's earlier point. The objects have a finite temperature, so they are giving off heat in the form of radiation. If they are side-by-side, then it should stand that the darker one is absorbing more heat than the lighter one. It will both absorb and emit more than the other

    The convection will be the same, but I would think that as negligible as it may be, the one should be slightly warmer because of this.
     
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