View factor

In radiative heat transfer, a view factor, F A → B {displaystyle F_{A ightarrow B}} , is the proportion of the radiation which leaves surface A {displaystyle A} that strikes surface B {displaystyle B} . In a complex 'scene' there can be any number of different objects, which can be divided in turn into even more surfaces and surface segments. In radiative heat transfer, a view factor, F A → B {displaystyle F_{A ightarrow B}} , is the proportion of the radiation which leaves surface A {displaystyle A} that strikes surface B {displaystyle B} . In a complex 'scene' there can be any number of different objects, which can be divided in turn into even more surfaces and surface segments. View factors are also sometimes known as configuration factors, form factors, angle factors or shape factors. Because radiation leaving a surface is conserved, the sum of all view factors from a given surface, S i {displaystyle S_{i}} , is unity: For example, consider a case where two blobs with surfaces A and B are floating around in a cavity with surface C. All of the radiation that leaves A must either hit B or C, or if A is concave, it could hit A. 100% of the radiation leaving A is divided up among A, B, and C. Confusion often arises when considering the radiation that arrives at a target surface. In that case, it generally does not make sense to sum view factors as view factor from A and view factor from B (above) are essentially different units. C may see 10% of A 's radiation and 50% of B 's radiation and 20% of C 's radiation, but without knowing how much each radiates, it does not even make sense to say that C receives 80% of the total radiation. For a convex surface, no radiation can leave the surface and then hit later, because radiation travels in straight lines. Hence, for convex surfaces, F A → A = 0 {displaystyle F_{A ightarrow A}=0} For concave surfaces, this doesn't apply, and so for concave surfaces F A → A > 0 {displaystyle F_{A ightarrow A}>0}