TABLE OF CONTENTS Temperature is a measure of molecular energy, or heat energy, and the potential to transfer heat energy. Four temperature scales were devised for the measurement of heat and heat transfer.
Three temperature scales are in common use to measure the relative hotness or coldness of a material. The scales are: Fahrenheit ( F) (attributed to Daniel G. Fahrenheit, 1724); Celsius ( C) (attributed to Anders Celsius, 1742); and Kelvin (K), which is based on the Celsius scale and is mainly used for scientific work. The Rankine scale ( R), based on the Fahrenheit scale, is less commonly used, but will be encountered.
The Fahrenheit scale is based on the freezing point of a saturated salt solution at sea level (14.7 psi or 101.36 kPa) and the internal temperature of oxen, which set the 0 and 100 point markers on the scale. The Celsius scale is based on the freezing point and the boiling point of pure water at sea level. The Kelvin and Rankine scales are referenced to absolute zero, which is the temperature at which all molecular motion ceases, or the energy of a molecule is zero. The temperatures of the freezing and boiling points of water decrease as the pressure decreases, and change with the purity of the water.
Conversion between the units is shown in Table 10.1.
| Reference Point | F | C | R | K |
|---|---|---|---|---|
| Water boiling point | 212 | 100 | 671.6 | 373.15 |
| Internal oxen temperature | 100 | 37.8 | 559.6 | 310.95 |
