Heat flux

Heat flux (or thermal flux, sometimes also referred to as heat flux density or heat flow rate intensity) is a flow of thermal energy per unit of area per unit of time.

$\vec{\phi}_q\;\left[\dfrac{\textrm{W}}{\textrm{m}^2}\right]$

the subscript $$q$$ specifying heat flux, as opposed to mass or momentum flux. Fourier’s law is an important application of these concepts. It has both a direction and a magnitude, and so it is a vector quantity. To define the heat flux at a certain point in space, one takes the limiting case where the size of the surface becomes infinitesimally small.

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