ISO 31-4 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to heat. It is superseded by ISO 80000-5.
Its definitions include:
|thermodynamic temperature||T, (Θ)||kelvin||K||The kelvin is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.||For practical measurements, the International Temperature Scale of 1990 defines several fixed points and interpolation procedures.|
|Celsius temperature||t, φ||degree Celsius||°C||The degree Celsius is a special name for the unit kelvin, for use in stating values of Celsius temperature.||t = T − T0, where T0 = 273.15 K|
|linear expansion coefficient||αl||reciprocal kelvin, kelvin to the power negative 1||K−1|
Annex A of ISO 31-4 lists units of heat based on the foot, pound and second and some other units, including the degree Rankine, degree Fahrenheit, British thermal unit and others. Annex B lists conversion factors for three versions of the calorie.
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