Heat_flux
Heat flux
Vector representing the energy passing through a given area per unit time
In physics and engineering, heat flux or thermal flux, sometimes also referred to as heat flux density[1], heat-flow density or heat-flow rate intensity, is a flow of energy per unit area per unit time. Its SI units are watts per square metre (W/m2). 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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Heat flux is often denoted , the subscript q specifying heat flux, as opposed to mass or momentum flux. Fourier's law is an important application of these concepts.