Heat flux or thermal flux is the rate of heat energy transfer through a given surface. The SI derived unit of heat rate is joule per second, or watt. Heat flux is the heat rate per unit area. In SI units, heat flux is measured in . Heat rate is a scalar quantity, while heat flux is a vectorial 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.
Heat flux is often denoted, the subscript q specifying heat rate, as opposed to mass or momentum rate. Fourier's law is an important application of these concepts.
Famous quotes containing the words heat and/or flux:
“Coal is a portable climate. It carries the heat of the tropics to Labrador and the polar circle; and it is the means of transporting itself whithersoever it is wanted. Watt and Stephenson whispered in the ear of mankind their secret, that a half-ounce of coal will draw two tons a mile, and coal carries coal, by rail and by boat, to make Canada as warm as Calcutta, and with its comfort brings its industrial power.”
—Ralph Waldo Emerson (18031882)
“Existence is no more than the precarious attainment of relevance in an intensely mobile flux of past, present, and future.”
—Susan Sontag (b. 1933)