The inward heat flux, q0, is often a sum of contributions from different heat transfer processes (for example, radiation and convection). The special case
q0 = 0 is called thermal insulation.
A common type of heat flux boundary conditions is one for which q0 = h·
(Text − T), where
Text is the temperature far away from the modeled domain and the heat transfer coefficient,
h, represents all the physics occurring between the boundary and “far away.” It can include almost anything, but the most common situation is that
h represents the effect of an exterior fluid cooling or heating the surface of a solid, a phenomenon often referred to as convective cooling or heating.