The Rankine Scale: Engineering's Absolute Temperature
The 華氏-Based Absolute Scale
Try 温度コンバーターWhile most of the world uses ケルビン for absolute temperature measurements, American engineers often work with a lesser-known scale: Rankine. Named after Scottish physicist William John Macquorn Rankine, this scale combines the absolute zero starting point of ケルビン with the degree size of 華氏.
If you've ever wondered why some US engineering textbooks use °R instead of K, this guide explains everything you need to know about the Rankine scale.
Who Was William Rankine?
William John Macquorn Rankine (1820-1872) was a Scottish mechanical engineer and physicist who made major contributions to thermodynamics, civil engineering, and naval architecture.
In 1859, Rankine proposed an absolute temperature scale based on 華氏 degrees, paralleling the ケルビン scale's relationship to 摂氏. His work on thermodynamics helped establish the field, and he coined the term "actual energy" (later called kinetic energy).
Rankine's contributions to engineering were so significant that the scale bearing his name remains in use in certain US industries more than 150 years later.
How Rankine Relates to Other Scales
The four common temperature scales can be organized into two pairs:
| Scale Type | Relative Scale | Absolute Scale |
|---|---|---|
| Metric | 摂氏 (°C) | ケルビン (K) |
| Imperial/US | 華氏 (°F) | Rankine (°R) |
Key relationships:
- Rankine to 華氏: °R = °F + 459.67
- Rankine to ケルビン: °R = K × 1.8
- Rankine to 摂氏: °R = (°C + 273.15) × 1.8
Why Use Rankine?
You might wonder: if ケルビン is the international standard, why does Rankine exist at all? The answer lies in the US engineering tradition.
Compatibility with US Units
US engineers working with 華氏-based systems (BTUs, pounds, feet) find Rankine more convenient than converting everything to metric. Thermodynamic calculations often require absolute temperatures, and using Rankine allows engineers to stay within the imperial/US customary system.
Thermodynamic Equations
Many thermodynamic equations require absolute temperature. For example, the ideal gas law (PV = nRT) only works correctly with absolute scales. US engineers using imperial units can use Rankine directly without converting to ケルビン.
Industry Applications
Rankine is still found in:
- US aerospace engineering
- American HVAC calculations
- Some petroleum industry applications
- US engineering education textbooks
Rankine Conversion Table
| Description | Rankine (°R) | ケルビン (K) | 華氏 (°F) | 摂氏 (°C) |
|---|---|---|---|---|
| Absolute Zero | 0 | 0 | −459.67 | −273.15 |
| Liquid Nitrogen | 139 | 77 | −321 | −196 |
| Water Freezes | 491.67 | 273.15 | 32 | 0 |
| Room Temperature | 527.67 | 293.15 | 68 | 20 |
| Body Temperature | 558.27 | 310.15 | 98.6 | 37 |
| Water Boils | 671.67 | 373.15 | 212 | 100 |
Rankine vs ケルビン: Key Differences
| Aspect | Rankine (°R) | ケルビン (K) |
|---|---|---|
| Zero Point | Absolute zero | Absolute zero |
| Degree Size | Same as 華氏 | Same as 摂氏 |
| Primary Use | US engineering | International science |
| Water Freezing | 491.67 °R | 273.15 K |
| Symbol | °R | K (no degree symbol) |
| SI Status | Not SI | SI 基本単位 |
Note: ケルビン doesn't use a degree symbol (it's just "K"), while Rankine traditionally uses "°R."
まとめ
The Rankine scale may not be as well-known as ケルビン, 摂氏, or 華氏, but it serves an important purpose in American engineering. By providing an absolute temperature scale that maintains compatibility with 華氏 and imperial units, Rankine allows US engineers to perform thermodynamic calculations without constantly converting between unit systems.
Whether you encounter Rankine in an engineering textbook, an HVAC calculation, or aerospace documentation, you now understand its purpose and how to convert to more familiar scales.