How can i calculate the exact amount of heat absorbed by a black paint

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Discussion Overview

The discussion revolves around calculating the exact amount of heat absorbed by black paint, particularly in the context of a steel plate painted black. Participants explore the theoretical and practical aspects of heat absorption, including the role of color, heat absorption coefficients, and the complexities of heat transfer mechanisms.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants suggest using the heat absorption coefficient to calculate temperature rise, but express difficulty in finding specific data for black paint.
  • Others propose treating a black-painted surface as a black body, which is a perfect absorber and radiator, while noting that this may not apply to other colors due to varying characteristics of different paints.
  • There is mention of the complexity of the problem due to multiple heat transfer methods, including convection, conduction, and radiation, as well as the temperature dependence of spectral emissivities.
  • One participant questions whether the temperature rise of the paint can be considered the final temperature of the steel plate, assuming efficient heat transfer from the paint to the metal.
  • Concerns are raised about the thermal conductivity of the paint and the conditions under which the steel plate would reach thermal equilibrium with the paint surface.
  • A participant shares an anecdote about a highly absorbent coating from 3M, highlighting the variability in paint absorption characteristics.

Areas of Agreement / Disagreement

Participants express a range of views on the methods and challenges of calculating heat absorption, with no consensus reached on the best approach or the validity of specific assumptions.

Contextual Notes

The discussion highlights limitations related to the availability of specific data on heat absorption coefficients for paints, the dependence on paint characteristics, and the influence of various heat transfer mechanisms.

chetanladha
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Hi.
Knowing the LRV, heat source and all other relevant details, how can we deduce the exact temp rise with black colour (or any other colour for that matter)??
 
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chetanladha said:
Hi.
Knowing the LRV, heat source and all other relevant details, how can we deduce the exact temp rise with black colour (or any other colour for that matter)??

What are your thoughts on the problem?
 
i think just like we do for metals, if we know the heat absorption coefficient, then it can be done.
But unfortunately i can't find anything named "heat absorption coefficient" for black colour.
Is there any equivalent?
 
If the body is painted black then you can get approximate answers by treating it as a black body(perfect absorber/radiator).For other colours you can refer to the heat absorption coefficient(emissivity)but I doubt if you can get perfect data because different paints,even those that might look the same,have different characteristics.To add to the complications some paints have spectral emissivities that are are temperature dependent.
It seems that you are tackling a problem that can very complicated.Radiation is not the only method of heat transfer since you also have convection and conduction and possibly evaporation/condensation.There are so many variables.
If you gave more details about what exactly it is you are trying to do people here might be able to give you more advice.Am I right in guessing that you are starting a project with an emphasis on practical work which is about comparing the radiation/absorption characteristics of different surfaces?
 
Dadface said:
If the body is painted black then you can get approximate answers by treating it as a black body(perfect absorber/radiator).For other colours you can refer to the heat absorption coefficient(emissivity)but I doubt if you can get perfect data because different paints,even those that might look the same,have different characteristics.To add to the complications some paints have spectral emissivities that are are temperature dependent.
It seems that you are tackling a problem that can very complicated.Radiation is not the only method of heat transfer since you also have convection and conduction and possibly evaporation/condensation.There are so many variables.
If you gave more details about what exactly it is you are trying to do people here might be able to give you more advice.Am I right in guessing that you are starting a project with an emphasis on practical work which is about comparing the radiation/absorption characteristics of different surfaces?

Hi.
My work is very close to comparing the radiation/absorption characteristics of metal plate painted with different colours.
So, if there is a steel plate painted black, can i take the rise in temperature of paint to be the final temperature of the steel plate. (Assuming that the paint passes all of its heat to the parent metal.)

Tackling individual paint or steel plate if fine, but does the same hold true when you are talking about a steel plate painted black?
 
chetanladha said:
Hi.
My work is very close to comparing the radiation/absorption characteristics of metal plate painted with different colours.
So, if there is a steel plate painted black, can i take the rise in temperature of paint to be the final temperature of the steel plate. (Assuming that the paint passes all of its heat to the parent metal.)

Tackling individual paint or steel plate if fine, but does the same hold true when you are talking about a steel plate painted black?

I think this is such a difficult problem to deal with theoretically because there are so many variables just one other being connected with the thermal conductivity of the paint.I think that if the paint is thin enough,and if all the surroundings have the same temperature,and if the plate is painted on all surfaces then it is fairly reasonable to assume that the plate will come to thermal equilibrium with the paint surface.
Try googling heat transfer coefficient and cooling zone.com
 
There are some very tricky variables! Many years ago, 3M was making a "Solar-Absorbent" coating that was super-black. My observing partner and I managed to cadge a supply of that material from an engineer at 3M so we could coat all the interior surfaces of our telescopes, adapters, eyepieces, etc with it. We couldn't legally buy it because the solvents were carcinogenic, but we managed to arrange to get an "engineering sample".

That stuff is WAY blacker and more absorbent than conventional paints.
 

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