Intensity (heat Transfer)

Intensity (heat Transfer)

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

where

• is the infinitesimal source area
• is the outgoing heat transfer from the area
• is the solid angle subtended by the infinitesimal 'target' (or 'aperture') area
• is the angle between the source area normal vector and the line-of-sight between the source and the target areas.

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:

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

The factor (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 ; note that the solid angle corresponding to a hemisphere is equal to steradians.

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