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In other words, heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from one atom to another. Conduction is the most significant means of heat transfer within a solid or between solid objects in thermal contact. Fluids—especially gases—are less conductive.
This mechanism is found very commonly in everyday life, including central heating and air conditioning and in many other machines. Forced convection is often encountered by engineers designing or analyzing heat exchangers, pipe flow, and flow over a plate at a different temperature than the stream (the case of a shuttle wing during re-entry, for example).
Heat radiation is the energy in the form of electromagnetic waves emitted by a solid, liquid, or gas as a result of its temperature. [37] In buildings, the radiant heat flow between two internal surfaces (or a surface and a person) is influenced by the emissivity of the heat emitting surface and by the view factor between this surface and the ...
Thermal insulation provides a region of insulation in which thermal conduction is reduced, creating a thermal break or thermal barrier, [1] or thermal radiation is reflected rather than absorbed by the lower-temperature body. The insulating capability of a material is measured as the inverse of thermal conductivity (k).
The compressor pumps the refrigerant gas up to high pressure and temperature. From there it enters a heat exchanger (sometimes called a condensing coil or condenser) where it loses heat to the outside, cools, and condenses into its liquid phase. An expansion valve (also called metering device) regulates the refrigerant liquid to flow at the ...
Underfloor heating pipes, before they are covered by the screed. Underfloor heating and cooling is a form of central heating and cooling that achieves indoor climate control for thermal comfort using hydronic or electrical heating elements embedded in a floor.
Internal flow occurs when a fluid is enclosed by a solid boundary such as when flowing through a pipe. An external flow occurs when a fluid extends indefinitely without encountering a solid surface. Both of these types of convection, either natural or forced, can be internal or external because they are independent of each other.
Ancient heating systems, including hearths, furnaces, and stoves, operated primarily through convection.Fixed central hearths, which were first excavated and retrieved in Greece, date back to 2500 BC, whereas crude fireplaces were used as early as the 800s AD and in the 13th century, when castles in Europe were built with fireplaces with a crude form of chimney.