What Is Rankine [°R]?
The Rankine degree, written as °R, is a temperature unit used in science and engineering. It starts at absolute zero and increases in the same size steps as the Fahrenheit scale.
Rankine is mostly used in some parts of engineering in the United States, especially when working with heat, energy, and gas laws.
Definition
The Rankine scale is an absolute temperature scale. This means:
- 0 °R is absolute zero, where all molecular motion stops.
- Rankine degrees are the same size as Fahrenheit degrees.
- The zero point is different from Fahrenheit, but the step size is the same.
Key relationships:
- From Fahrenheit to Rankine: T(°R) = T(°F) + 459.67
- From Kelvin to Rankine: T(°R) = T(K) × 9 ÷ 5
So if you know the temperature in Fahrenheit or Kelvin, you can easily find the temperature in Rankine.
History / Origin
The Rankine scale is named after William John Macquorn Rankine, a Scottish engineer and physicist from the 1800s.
In the 19th century, scientists wanted absolute temperature scales that start at absolute zero. Lord Kelvin created such a scale based on Celsius. Rankine did a similar thing, but based his scale on Fahrenheit instead.
Because many engineers in the United States were already used to Fahrenheit, the Rankine scale became useful in fields like thermodynamics and steam engineering.
Symbol & Abbreviation
The main symbol and short forms for Rankine are:
- Symbol: °R
- Also seen as: R or Rankine, especially in older books
When writing temperatures, the degree sign comes before the letter R. For example, 520 °R.
Current Use Around the World
Today, Rankine is not very common in everyday life. Most people use Celsius or Fahrenheit for weather and daily temperatures.
Rankine is still used in some areas:
- Thermodynamics: studying heat, energy, and work.
- Mechanical and aerospace engineering: especially in the United States.
- Gas turbines, jet engines, and power plants: some design calculations use Rankine.
Outside the United States, most scientists and engineers prefer Kelvin instead of Rankine because Kelvin matches the metric system.
Example Conversions
Here are the main formulas you need:
- Fahrenheit to Rankine: T(°R) = T(°F) + 459.67
- Rankine to Fahrenheit: T(°F) = T(°R) − 459.67
- Kelvin to Rankine: T(°R) = T(K) × 9 ÷ 5
- Rankine to Kelvin: T(K) = T(°R) × 5 ÷ 9
Example 1, 32 °F to Rankine
- Start with the formula: T(°R) = T(°F) + 459.67
- Put in the value: T(°R) = 32 + 459.67
- Result: T(°R) = 491.67 °R
Example 2, 300 K to Rankine
- Use: T(°R) = T(K) × 9 ÷ 5
- Put in the value: T(°R) = 300 × 9 ÷ 5
- Compute: 300 × 9 = 2700
- Then: 2700 ÷ 5 = 540
- Result: T(°R) = 540 °R
Example 3, 672 °R to Fahrenheit
- Use: T(°F) = T(°R) − 459.67
- Put in the value: T(°F) = 672 − 459.67
- Result: T(°F) ≈ 212.33 °F
Example 4, 900 °R to Kelvin
- Use: T(K) = T(°R) × 5 ÷ 9
- Put in the value: T(K) = 900 × 5 ÷ 9
- Compute: 900 × 5 = 4500
- Then: 4500 ÷ 9 = 500
- Result: T(K) = 500 K
Related Units
The Rankine scale is closely related to these temperature units:
- Kelvin (K) absolute temperature scale based on Celsius, used in science worldwide.
- Celsius (°C) everyday and scientific scale in most countries, water freezes at 0 °C and boils at 100 °C at standard pressure.
- Fahrenheit (°F) everyday and weather scale mostly in the United States, water freezes at 32 °F and boils at 212 °F at standard pressure.
Helpful links between these units:
- T(°R) and T(°F) use the same degree size.
- T(K) and T(°C) use the same degree size.
- T(°R) and T(K) are both absolute temperature scales.
FAQs
What is Rankine used for?
Rankine is mainly used in thermodynamics, heat transfer, and some engineering work in the United States. It is helpful when formulas were made using Fahrenheit.
How is Rankine different from Kelvin?
Both start at absolute zero, but their degree sizes are different. Rankine uses the same step size as Fahrenheit. Kelvin uses the same step size as Celsius.
Why does Fahrenheit plus 459.67 give Rankine?
The Fahrenheit and Rankine scales are shifted by 459.67 degrees. At absolute zero, the temperature is −459.67 °F. So if you add 459.67, you get 0 °R at that point.
Can Rankine temperatures be negative?
No. Rankine is an absolute scale that starts at absolute zero. That point is 0 °R. Any real physical temperature is 0 °R or higher.
Why is Rankine not common in daily life?
Rankine is designed for scientific and engineering use, not for everyday weather or cooking. People find Celsius and Fahrenheit easier for daily activities.
Which is better to learn first, Kelvin or Rankine?
Most students learn Kelvin first, because it matches the metric system and is used more around the world. Rankine is helpful later if you work with older US based engineering systems.
Is Rankine still taught today?
Yes, but usually only in college level engineering, physics, and thermodynamics courses, especially in countries that use Fahrenheit in technical fields.