Heat flux


Heat flux

Heat flux or thermal flux is a flow of energy per unit of area per unit of time. In SI units, it is measured in [W·m-2] . It has both a direction and a magnitude so it 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 overrightarrow{phi_q}, the subscript "q" specifying "heat" flux, as opposed to "mass" or "momentum" flux. The most important appearance of heat flux in physics is in Fourier's law describing heat conduction.

Measuring heat flux

The measurement of heat flux is most often done by measuring a temperature difference over a piece of material with known thermal conductivity. This method is analogous to a standard way to measure an electric current, where one measures the voltage drop over a known resistor.

Relevance to science and engineering

One of the tools in a scientist's or engineer's toolbox is the energy balance. Such a balance can be set up for any physical system, from chemical reactors to living organisms, and generally takes the following form

: frac{partial E_{in{partial t} - frac{partial E_{out{partial t} - frac{partial E_{accumulated{partial t} = 0where the three frac{partial E}{partial t} terms stand for the time rate of change of respectively the total amount of incoming energy, the total amount of outgoing energy and the total amount of accumulated energy.

Now, if the only way the system exchanges energy with its surroundings is through heat transfer, the heat flux can be used to calculate the energy balance, since

: frac{partial E_{in{partial t} - frac{partial E_{out{partial t} = oint_S overrightarrow{phi_q} cdot , overrightarrow{dS}where we have integrated the heat flux overrightarrow{phi_q} over the surface S of the system.

In real-world applications of course one cannot know the heat flux at every point on the surface, but intelligent estimates to calculate the integral can be made, for example through Monte Carlo integration.

ee also

*Heat#Notation
*Heat conduction
*Heat transfer
*Critical heat flux
*Latent heat flux
*Rate of heat flow
*Insolation
*Heat flux sensor


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • heat flux — šilumos srautas statusas T sritis Standartizacija ir metrologija apibrėžtis Šilumos kiekis, pereinantis per tam tikrą paviršių per vienetinį laiko tarpą. atitikmenys: angl. heat flow; heat flow rate; heat flux; thermal flow; thermal flux vok.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • heat flux — šilumos srautas statusas T sritis fizika atitikmenys: angl. heat flow; heat flux; thermal flow; thermal flux vok. Wärmefluß, m; Wärmeströmung, f; Wärmestrom, m rus. поток тепла, m; тепловой поток, m pranc. flux de chaleur, m …   Fizikos terminų žodynas

  • heat flux — šilumos srautas statusas T sritis Energetika apibrėžtis Šilumos kiekis, praeinantis per tam tikrą paviršių per vienetinį laiko tarpą. atitikmenys: angl. heat flux; thermal flux vok. Wärmefluß, m; Wärmeströmung, f rus. поток тепла, m; тепловой… …   Aiškinamasis šiluminės ir branduolinės technikos terminų žodynas

  • heat flux — šilumos srautas statusas T sritis ekologija ir aplinkotyra apibrėžtis Šilumos kiekis, praeinantis per tam tikrą paviršių per vienetinį laiko tarpą. SI vienetas – W/m². atitikmenys: angl. heat flow; heat flux vok. Wärmefluss, m; Wärmestrom, m rus …   Ekologijos terminų aiškinamasis žodynas

  • heat flux — the rate of heat flowing past a reference datum. Its units are W/m2 …   Mechanics glossary

  • heat flux — Смотри тепловой поток …   Энциклопедический словарь по металлургии

  • Heat flux sensor — A heat flux sensor is a commonly used name for a transducer generating a signal that is proportional to the local heat flux. This heat flux can have different origins; in principle convective , radiative as well as conductive heat can be measured …   Wikipedia

  • heat flux density — šilumos srauto tankis statusas T sritis fizika atitikmenys: angl. heat flow density; heat flux density vok. Wärmestromdichte, f rus. плотность теплового потока, f pranc. densité de courant thermique, f; densité de flux de chaleur, f …   Fizikos terminų žodynas

  • Critical heat flux — describes the thermal limit of a phenomenon where a phase change occurs during heating (such as bubbles forming on a metal surface used to heat water), which suddenly decreases the efficiency of heat transfer, thus causing localised overheating… …   Wikipedia

  • Latent heat flux — is the flux of heat from the Earth s surface to the atmosphere that is associated with evaporation of water at the surface and subsequent condensation of water vapor in the troposphere. It is an important component of Earth s surface energy… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.