Two objects in a shaded positio

  • Thread starter Thread starter GIW
  • Start date Start date
AI Thread Summary
In a shaded position, two objects of the same mass and volume, one white and one black, are discussed regarding their temperature differences. The black object may initially be warmer due to its higher absorption of heat, influenced by factors like wind exposure and indirect radiation. While both objects will reach thermal equilibrium over time, the darker object will experience a greater heat flux on its surface in transient conditions. The emissivity of the black object allows it to absorb and emit heat more effectively than the white object. Overall, the black object is likely to be slightly warmer than the white one in shaded conditions.
GIW
Messages
2
Reaction score
0
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
 
Engineering news on Phys.org


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.
 
Thread 'I need a concave mirror with a focal length length of 150 feet'
I need to cut down a 3 year old dead tree from top down so tree causes no damage with small pieces falling. I need a mirror with a focal length of 150 ft. 12" diameter to 36" diameter will work good but I can't think of any easy way to build it. Nothing like this for sale on Ebay. I have a 30" Fresnel lens that I use to burn stumps it works great. Tree service wants $2000.
Hi all, i have some questions about the tesla turbine: is a tesla turbine more efficient than a steam engine or a stirling engine ? about the discs of the tesla turbine warping because of the high speed rotations; does running the engine on a lower speed solve that or will the discs warp anyway after time ? what is the difference in efficiency between the tesla turbine running at high speed and running it at a lower speed ( as fast as possible but low enough to not warp de discs) and: i...
Back
Top