Two objects in a shaded positio

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Discussion Overview

The discussion revolves around the thermal properties of two objects, one white and one black, placed in a shaded position with the same mass and volume. Participants explore whether the darker object will be hotter than the lighter one under certain conditions, considering factors such as ambient temperature, radiation, and heat transfer mechanisms.

Discussion Character

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

Main Points Raised

  • Some participants suggest that the darker object may have a higher initial temperature or may warm faster due to being more exposed to environmental conditions.
  • It is proposed that radiation heat transfer is influenced by the temperature difference and the emissivity of the materials, with black bodies having a higher emissivity.
  • One participant questions whether indirect sunlight would heat the black object faster than the white one.
  • There is a discussion about steady state versus transient conditions, with some arguing that under steady state, both objects should reach the same temperature, while under transient conditions, the darker object may experience a greater heat flux.
  • Another point raised is that the darker object absorbs and emits heat more effectively than the lighter one, potentially leading to it being slightly warmer.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the thermal behavior of the two objects, with no consensus reached on whether the darker object will definitively be hotter than the lighter one.

Contextual Notes

The discussion includes assumptions about steady state versus transient conditions, the influence of ambient temperature, and the effects of radiation and convection, which remain unresolved.

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
 
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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.
 


So if i am understanding you correctly, indirect sun will heat up the black object faster than the white one?
 


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.
 


CarlAK said:
radiation coefficient (don't recall the term), 1.0 for black body.

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.
 


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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