Heat is a form of energy, also called thermal energy. In thermodynamics (also heat theory) heat is a process variable; it is exchanged with the environment by a thermodynamic system in certain processes. In the framework of statistical mechanics, heat is interpreted as the energy of the disordered movement of the atomic or molecular components of matter.
Thermal energy (heat energy) production mechanism
Heat is generated in many physical and chemical processes, such as;
in the combustion of fuels and fuels (→ combustion enthalpy)
by friction from mechanical energy
in the conduction of electrical current through resistive conductors (eg high voltage power lines)
in the absorption of light and other types of radiation in matter
Conversely, thermal energy can be at least partially converted into other forms of energy, eg. B. by means of heat engines in mechanical energy or directly in thermal radiation and (at high temperatures) in light (eg., In incandescent lamps). Our thermal energy review article goes ahead from below.
High and low temperature heat – thermal energy
Heat energy, thermal energy, can occur at different temperature levels:
The value of heat at high temperatures is higher than that of low-temperature heat: it is more versatile, but also tends to be more expensive to win. It is best to avoid using low-temperature heat simply from high-temperature heat.
High temperature heat (at temperatures of hundreds of ° C or higher) is needed for heat engines (such as in power plants). It can be obtained by combustion processes or from electrical energy.
Low-temperature heat (at temperatures of, for example, below 100 ° C., often even below 50 ° C.) is required in particular for heating purposes.
High-temperature heat can be considered as a higher-quality form of energy than low-temperature heat, because it offers more options, such as the more efficient conversion into mechanical energy. For example, if a geothermal reservoir or a source of waste heat supplies only temperatures of 80 ° C, this is usually insufficient for the production of electrical energy. Such heat can only z. B. used for heating purposes. The “valence” of heat can be expressed as exergy content.
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