Intensity (heat transfer)

For other uses, see Intensity (disambiguation).

In the field of heat transfer, intensity of radiation I is a measure of the distribution of radiant heat flux per unit area and solid angle, in a particular direction, defined according to

dq = I\, d\omega\, \cos \theta\, dA

where

Typical units of intensity are W·m−2·sr−1.

Intensity can sometimes be called radiance, especially in other fields of study.

The emissive power of a surface can be determined by integrating the intensity of emitted radiation over a hemisphere surrounding the surface:

q = \int_{\phi=0}^{2\pi} \int_{\theta=0}^{\pi/2} I \cos \theta \sin \theta d\theta d\phi

For diffuse emitters, the emitted radiation intensity is the same in all directions, with the result that

E = \pi I

The factor \pi (which really should have the units of steradians) is a result of the fact that intensity is defined to exclude the effect of reduced view factor at large values \theta; note that the solid angle corresponding to a hemisphere is equal to 2\pi steradians.

Spectral intensity I_\lambda is the corresponding spectral measurement of intensity; in other words, the intensity as a function of wavelength.

See also

References

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