or heat flow
is the process whereby heat
flows from regions of higher to regions of lower temperature
The rate of heat flow depends on the mode of heat transfer and on the temperature difference across which the heat flows, as well as on the matter of the system under consideration and its geometry.
There are three types of heat flow:
For room temperature objects, the majority of photons emitted (and involved in radiative heat transfer) are in the infrared
spectrum, but this is by no means the only frequency range involved in radiation. Hotter objects transfer heat in the visible spectrum or beyond. Whenever EM radiation is emitted and then absorbed, heat is transferred. This principle is used in microwave ovens, laser cutting, and RF
The electrons of a metallic solid conduct nearly all of the heat through the solid. Electrons also conduct electric current through conductive solids, and the thermal and electrical conductivities of most metals have about the same ratio. A good electrical conductor, such as copper, also conducts heat well.
The Peltier Effect exhibits the propensity of electrons to conduct heat through an electrically conductive solid.
Weatherization slows convective heat flow in buildings. Insulation slows conductive heat flow. Reflective barriers slow radiative heat flow, and often couple directly with insulation.
For more on heat transfer, see heat.