Rankine (°R)
The Rankine scale is an absolute temperature scale using Fahrenheit-sized degrees, with zero at absolute zero (−0°R = −459.67°F). Named after Scottish engineer William John Macquorn Rankine, it is to Fahrenheit what kelvin is to Celsius. Rankine is used in some American engineering applications, particularly in thermodynamics and HVAC calculations.
Definition
Zero Rankine (0°R) equals absolute zero (−459.67°F or −273.15°C or 0 K). One Rankine degree has the same magnitude as one Fahrenheit degree. To convert Fahrenheit to Rankine, add 459.67. To convert Rankine to kelvin, multiply by 5/9. Water freezes at 491.67°R and boils at 671.67°R.
History
William John Macquorn Rankine proposed the scale in 1859, five years after Lord Kelvin proposed the absolute Celsius-based scale. Rankine argued that engineers accustomed to Fahrenheit would benefit from an absolute scale using the same degree size. The scale gained traction in American engineering, particularly in fields like thermodynamics, combustion analysis, and refrigeration, where absolute temperatures are needed but Fahrenheit is the customary unit. Outside the US, Rankine is rarely encountered, as kelvin serves the same purpose for Celsius-based systems.
Common Uses
American engineering textbooks and some HVAC calculations use Rankine for thermodynamic equations that require absolute temperature, such as the ideal gas law and Carnot efficiency calculations. Some US aerospace and combustion engineers use Rankine. The Rankine cycle, a thermodynamic model for steam power plants, is named after the same William Rankine but uses kelvin or Rankine degrees depending on the convention.
Did You Know? Facts About Rankine
- Rankine is to Fahrenheit what kelvin is to Celsius - same degree size, different zero point.
- Room temperature (72°F) is about 531.67°R.
- The Rankine cycle, used in power plant engineering, is named after the same William Rankine who proposed the temperature scale.
- Rankine is almost exclusively used in the United States - it is virtually unknown in European engineering.
- William Rankine was also a pioneer in soil mechanics, thermodynamics, and civil engineering - not just temperature scales.