Translations of Encyclopedia about Physics

Heat Transfer

Heat can be transferred from one substance to another, a phenomenon used for example during the transfer of heat. By this we understand such a transfer of heat between adjacent lying particles. Particles from the warmer part of a substance transfer their kinetic energy by colliding into particles located in the cooler area. The degree to which heat energy can be transferred depends on heat conductivity (the ability to transfer heat). For example, metals are good conductors of heat but wood is a very poor conductor of heat.

Another method of how heat can be transferred is through heat radiation. In this way, heat transfers without the need for other substances.

Yet another form of transferring heat is convection, which is accomplished through flowing gases or liquids.

An example of heat being transferred through flow or heat radiation is hot water heating. This type of heating is used to transfer energy generated within a boiler, heated with the use of coal or oil. By burning these fuels, energy is transferred to the water circulating within the boiler. The heated water has a smaller density, for which reason it rises, transferring its gained energy to a radiator or radiators. Heat energy is then further transferred within the radiators between the heated water and the air surrounding the radiator. The heated air surrounding the radiator in turn transfers its gained energy according to the principle of heat radiation: the heated air above the radiator rises and is replaced by cooler air drawn from below the radiator. By this process, the air within a closed environment gradually becomes warmer.

Heat transfer can be hastened and made more effective by the use of pumps. By the use of water pumps, heat energy is drawn from a certain medium with a lower temperature (heat source) and transferred to a medium with a higher temperature (heat storage). The principle of how a heat pump operates is similar to a refrigerator’s compressor, where the operating liquid medium is evaporated in the vaporiser due to the surrounding temperature (of the heat source) and then compressed in the compressor. During this process, both pressure and temperature increase, after which water is passed through the compressor and then circulated through the heating circuit. The working medium condenses and then resent to the vaporiser.

A heat pump is more effective the smaller the difference between the heat source and the heat storage. The disadvantage of a heat pump is that it absorbs heat from surrounding objects, as such cooling the environment in which it is located (such as for example a floor space).

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