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Absorptance

Ability of a material to absorb radiant energy From Wikipedia, the free encyclopedia

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In the study of heat transfer, absorptance of the surface of a material is its effectiveness in absorbing radiant energy. It is the ratio of the absorbed to the incident radiant power.[1]

Mathematical definitions

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Hemispherical absorptance

Hemispherical absorptance of a surface, denoted A is defined as[2]

where

  • is the radiant flux absorbed by that surface;
  • is the radiant flux received by that surface.

Spectral hemispherical absorptance

Spectral hemispherical absorptance in frequency and spectral hemispherical absorptance in wavelength of a surface, denoted Aν and Aλ respectively, are defined as[2]

where

  • is the spectral radiant flux in frequency absorbed by that surface;
  • is the spectral radiant flux in frequency received by that surface;
  • is the spectral radiant flux in wavelength absorbed by that surface;
  • is the spectral radiant flux in wavelength received by that surface.

Directional absorptance

Directional absorptance of a surface, denoted AΩ, is defined as[2]

where

  • is the radiance absorbed by that surface;
  • is the radiance received by that surface.

Spectral directional absorptance

Spectral directional absorptance in frequency and spectral directional absorptance in wavelength of a surface, denoted Aν,Ω and Aλ,Ω respectively, are defined as[2]

where

  • is the spectral radiance in frequency absorbed by that surface;
  • is the spectral radiance received by that surface;
  • is the spectral radiance in wavelength absorbed by that surface;
  • is the spectral radiance in wavelength received by that surface.
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Other radiometric coefficients

More information Quantity, SI units ...
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References

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