Radiation :-
Heat transfer through radiation takes place in form of electromagnetic waves mainly in the infrared region.
Radiation emitted by a body is a consequence of thermal agitation of its composing molecules. Radiation heat transfer can be described by a reference to the so-called 'black body'.
A black body is defined as a body that absorbs all radiation that falls on its surface.
Actual black bodies don't exist in nature - though its characteristics are approximated by a hole in a box filled with highly absorptive material.
The emission spectrum of such a black body was first fully described by Max Planck.
A black body is a hypothetic body that completely absorbs all wavelengths of thermal radiation incident on it. Such bodies do not reflect light, and therefore appear black if their temperatures are low enough so as not to be self-luminous. All blackbodies heated to a given temperature emit thermal radiation.
The radiation energy per unit time from a blackbody is proportional to the fourth power of the absolute temperature and can be expressed with
Stefan-Boltzmann Law as
Heat transfer through radiation takes place in form of electromagnetic waves mainly in the infrared region.
Radiation emitted by a body is a consequence of thermal agitation of its composing molecules. Radiation heat transfer can be described by a reference to the so-called 'black body'.
The Black Body
A black body is defined as a body that absorbs all radiation that falls on its surface.
Actual black bodies don't exist in nature - though its characteristics are approximated by a hole in a box filled with highly absorptive material.
The emission spectrum of such a black body was first fully described by Max Planck.
A black body is a hypothetic body that completely absorbs all wavelengths of thermal radiation incident on it. Such bodies do not reflect light, and therefore appear black if their temperatures are low enough so as not to be self-luminous. All blackbodies heated to a given temperature emit thermal radiation.
The radiation energy per unit time from a blackbody is proportional to the fourth power of the absolute temperature and can be expressed with
Stefan-Boltzmann Law as
q = σ T4 A (1)
where
q = heat transfer per unit time (W)
σ = 5.6703 10-8 (W/m2K4) - The Stefan-Boltzmann Constant
T = absolute temperature Kelvin (K)
A = area of the emitting body (m2)
The Stefan-Boltzmann Constant in Imperial Units
σ = 5.6703 10-8 (W/m2K4)
= 0.1714 10-8 ( Btu/(h ft2 oR4) )
= 0.119 10-10 ( Btu/(h in2 oR4) )
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