n. The heat transfer rate per unit area as thermal radiation.

• Discussion

Radiant heat flux is typically calculated or measured for a specific surface to determine the heat transfer at that surface. Because all objects above a temperature of absolute zero radiate thermal energy, the net radiant heat transfer between two objects of the same radiation characteristics depends on their temperature difference, as shown in the diagram below (see "more").

more...

Related to wildland fire, the assumption is commonly made that flames (the hotter “surface”) and fuel have similar radiation characteristics. The following equation describes the factors that determine the radiant heat flux from surface 1 incident at surface 2. where:

• q″1,2 = incident radiant heat flux from object 1 to object 2 (W/m2);

• F1,2 = radiation view factor, the fraction of the radiation leaving the surface of object 1 that is incident at the surface of object 2 (dimensionless);

• ε1 = emissivity of object 1, the fraction of the radiation emitted by a blackbody at the same temperature as object 1 (object 1 is called a “graybody”);

• σ = Stefan-Boltzmann constant, relates the absolute temperature of an object to its theoretical maximum radiation emission per unit area (W/m2/K4);

• T1 = The absolute temperature of object 1 (K).

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• Notes

• Jack Cohen, Research Physical Scientist

Rocky Mountain Research Station

• August 2007