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William Thomson (1824-1907) was one of the great minds of the mid Nineteenth Century, but the SI unit of thermodynamic temperature named in his honor is seldom used except for scientific work. |
Purpose: The proposed unit of thermodynamic temperature assigns an exact value of 1000 to the triple point of water, thus creating a temperature scale convenient for both everyday use and precise scientific work. The proposed unit should eliminate the need for the Celsius and Fahrenheit relative temperature scales.
For the historical background, please see A Brief History of Temperature Measurement.
Merits of Temperature Scales: The Fahrenheit temperature scale remains the most intuitive temperature scale with 0°F representing really cold weather and 100°F representing really hot weather (at least for those of us living in the temperate zones.) The great drawback of Fahrenheit temperature is the freezing point of water at 32°F, a rather unintuitive value.
The freezing point of water is the most critical temperature for life on Earth. The Celsius temperature scale clearly denotes the freezing point of water as 0°C. Unfortunately, all temperatures below the freezing point of water have a negative Celsius temperature, a bit of a problem for those of us living outside the Tropics. The degree Celsius is 80% larger than the degree Fahrenheit, a rather course measurement unit in a age of ever more precise temperature measurement.
A thermodynamic temperature scale is vastly preferable to either the Celsius or Fahrenheit temperature scale. Unfortunately the choice of units for the Kelvin and Rankine thermodynamic scales give really strange values for everyday temperatures. The freezing point of water is 273.15 K, the triple point is 273.16 K, room temperature is about 295 K, body temperature is 310.15 K, and the boiling point of water is 373.15 K. The Rankine scale gives values that are just as meaningless. The freezing point of water is 491.67°R, the triple point is 491.688°R, room temperature is about 531°R, body temperature is 558.27°R, and the boiling point of water is 671.67°R.
Rationale for Proposed Unit: A thermodynamic temperature scale can only be successful for everyday use if it produces values that make sense to people. A room temperature of 295 K or 531°R makes little sense to most people.
The freezing point of water is an important temperature. Fortunately, the freezing point is only 0.010 K below the triple point of water. It therefore seems pretty logical to assign the value 0 to thermodynamic absolute zero and 1000 to the triple point of water. This creates a thermodynamic temperature with units equal to 0.273160 K or 0.491688°R.
With the proposed thermodynamic temperature unit, the freezing point of water is 999.963, or very nearly 1000. Room temperature is about 1080 and body temperature is about 1135. The boiling point of water is about 1366 and a hot oven is 1800. The table below compares Fahrenheit, Celsius, Kelvin, and the proposed thermodynamic temperature scale:
| Temperature Scales | Significance of Temperature | |||
|---|---|---|---|---|
| Fahrenheit | Celsius | Kelvin | Proposed | |
| 48,709.13°F | 27,042.85°C | 27,316 K.00 | 100,000 t.00 | One hundred times as hot as triple point of water |
| 24,124.73°F | 13,384.85°C | 13,658 K.00 | 50,000 t.00 | Fifty times as hot as triple point of water |
| 11,832.53°F | 6,555.85°C | 6,829 K.00 | 25,000 t.00 | Twenty-five times as hot as triple point of water |
| 9,944.45°F | 5,506.92°C | 5,780.07 K | 21,160 t.00 | Blackbody temperature of visible surface of Sun |
| 9,374.09°F | 5,190.05°C | 5,463.20 K | 20,000 t.00 | Twenty times as hot as triple point of water |
| 6,915.65°F | 3,824.25°C | 4,097.40 K | 15,000 t.00 | Fifteen times as hot as triple point of water |
| 6,169.76°F | 3,409.87°C | 3,683.02 K | 13,438 t.00 | Freezing point of tungsten |
| 4,457.21°F | 2,458.45°C | 2,731.60 K | 10,000 t.00 | Ten times as hot as triple point of water |
| 3,965.52°F | 2,185.29°C | 2,458.44 K | 9,000 t.00 | Nine times as hot as triple point of water |
| 3,473.83°F | 1,912.13°C | 2,185.28 K | 8,000 t.00 | Eight times as hot as triple point of water |
| 3,034.26°F | 1,667.92°C | 1,941.07 K | 7,106 t.00 | Freezing point of titanium |
| 2,982.15°F | 1,638.97°C | 1,912.12 K | 7,000 t.00 | Seven times as hot as triple point of water |
| 2,490.46°F | 1,365.81°C | 1,638.96 K | 6,000 t.00 | Six times as hot as triple point of water |
| 1,998.77°F | 1,092.65°C | 1,365.80 K | 5,000 t.00 | Five times as hot as triple point of water |
| 1,984.32°F | 1,084.62°C | 1,357.77 K | 4,970.60 t | Standard freezing point of copper |
| 1,947.53°F | 1,064.18°C | 1,337.33 K | 4,895.78 t | Standard freezing point of gold |
| 1,763.20°F | 961.78°C | 1,234.93 K | 4,520.90 t | Standard freezing point of silver |
| 1,507.08°F | 819.49°C | 1,092.64 K | 4,000 t.00 | Four times as hot as triple point of water |
| 1,220.58°F | 660.32°C | 933.47 K | 3,417.31 t | Standard freezing point of aluminum |
| 1,015.39°F | 546.33°C | 819.48 K | 3,000 t.00 | Three times as hot as triple point of water |
| 787.15°F | 419.53°C | 692.68 K | 2,535.79 t | Standard freezing point of zinc |
| 523.71°F | 273.17°C | 546.32 K | 2,000 t.00 | Twice as hot as triple point of water |
| 474.54°F | 245.85°C | 519.00 K | 1900 t.00 | Very hot oven |
| 449.47°F | 231.93°C | 505.08 K | 1849.02 t | Standard freezing point of tin |
| 425.37°F | 218.54°C | 491.69 K | 1800 t.00 | Hot oven |
| 376.20°F | 191.22°C | 464.37 K | 1700 t.00 | Medium oven |
| 327.03°F | 163.91°C | 437.06 K | 1600 t.00 | Low oven |
| 313.88°F | 156.60°C | 429.75 K | 1573.25 t | Standard freezing point of indium |
| 277.86°F | 136.59°C | 409.74 K | 1500 t.00 | 50% hotter than triple point of water |
| 228.69°F | 109.27°C | 382.42 K | 1400 t.00 | 40% hotter than triple point of water |
| 212°F.00 | 100°C.00 | 373.15 K | 1366.05 t | Standard boiling point of water |
| 179.52°F | 81.96°C | 355.11 K | 1300 t.00 | 30% hotter than triple point of water |
| 136.00°F | 57.78°C | 330.93 K | 1211.48 t | World record high air temperature |
| 130.36°F | 54.64°C | 327.79 K | 1200 t.00 | 20% hotter than triple point of water |
| 120.52°F | 49.18°C | 322.33 K | 1180 t.00 | Extremely hot air temperature |
| 110.69°F | 43.72°C | 316.87 K | 1160 t.00 | Very hot air temperature |
| 100.85°F | 38.25°C | 311.40 K | 1140 t.00 | Hot air temperature |
| 98.60°F | 37.00°C | 310.15 K | 1135.42 t | Human body temperature reference |
| 91.02°F | 32.79°C | 305.94 K | 1120 t.00 | Very warm air temperature |
| 85.58°F | 29.76°C | 302.91 K | 1108.93 t | Standard melting point of gallium |
| 81.19°F | 27.33°C | 300.48 K | 1100 t.00 | Warm air temperature |
| 71.35°F | 21.86°C | 295.01 K | 1080 t.00 | Moderate air temperature |
| 61.52°F | 16.40°C | 289.55 K | 1060 t.00 | Cool air temperature |
| 51.69°F | 10.94°C | 284.09 K | 1040 t.00 | Very cool air temperature |
| 41.85°F | 5.47°C | 278.62 K | 1020 t.00 | Cold air temperature |
| 39.15°F | 3.97°C | 277.12 K | 1014.50 t | Temperature of maximum water density |
| 32.02°F | 0.01°C | 273.16 K | 1000 t.00 | Triple point of water |
| 32°F.00 | 0°C.00 | 273.15 K | 999.96 t | Standard freezing point of water |
| 0°F.00 | -17.78°C | 255.37 K | 934.88 t | Fahrenheit's zero |
| -17.15°F | -27.31°C | 245.84 K | 900 t.00 | 90% as warm as triple point of water |
| -37.90°F | -38.83°C | 234.32 K | 857.80 t | Triple point of mercury |
| -66.32°F | -54.62°C | 218.53 K | 800 t.00 | 80% as warm as triple point of water |
| -115.49°F | -81.94°C | 191.21 K | 700 t.00 | 70% as warm as triple point of water |
| -128.56°F | -89.20°C | 183.95 K | 673.41 t | World record low air temperature |
| -164.66°F | -109.25°C | 163.90 K | 600 t.00 | 60% as warm as triple point of water |
| -213.83°F | -136.57°C | 136.58 K | 500 t.00 | Half as warm as triple point of water |
| -262.99°F | -163.89°C | 109.26 K | 400 t.00 | 40% as warm as triple point of water |
| -308.82°F | -189.34°C | 83.81 K | 306.80 t | Triple point of argon |
| -312.16°F | -191.20°C | 81.95 K | 300 t.00 | 30% as warm as triple point of water |
| -361.33°F | -218.52°C | 54.63 K | 200 t.00 | 20% as warm as triple point of water |
| -361.82°F | -218.79°C | 54.36 K | 199 t.00 | Triple point of molecular oxygen |
| -410.50°F | -245.83°C | 27.32 K | 100 t.00 | One tenth as warm as triple point of water |
| -415.47°F | -248.59°C | 24.56 K | 89.90 t | Triple point of neon |
| -434.82°F | -259.35°C | 13.80 K | 50.53 t | Triple point of molecular hydrogen |
| -454.75°F | -270.42°C | 2.73 K | 10 t.00 | One one-hundredth as warm as triple point of water |
| -459.18°F | -272.88°C | 0.27 K | 1 t.00 | One one-thousandth as warm as triple point of water |
| -459.67°F | -273.15°C | 0 K.00 | 0 t.00 | Thermodynamic absolute zero |
In the table above I have rather arbitrarily used a lower-case "t" as the symbol for the proposed thermodynamic temperature unit. There are many possible names for the proposed unit. William Thomson could be honored with the unit name "thomson" or merely "thom". Others worthy of honor include Ole Christensen Rømer (1644-1710), Guillaume Amontons (1663-1705), Jakob Hermann (1678-1733), Daniel Bernoulli (1700-1782), Pierre-Simon Laplace (1749-1827), Jean Baptiste Joseph Fourier (1768-1830), Sadi Carnot (1796-1832), Hermann Ludwig Ferdinand von Helmholtz (1821-94), Rudolf Julius Emmanuel Clausius (1822-88), James Clerk Maxwell (1831-79), Josiah Willard Gibbs (1839-1903), Ludwig Boltzmann (1844-1906), and Max Karl Ernst Ludwig Planck (1858-1947). The proposed unit could also be given a contrived name such as "thermo" or "tem".
The formula table below shows the relationships among Fahrenheit, Celsius, Kelvin, and the proposed thermodynamic temperature scale:
| tF | tF = (tC×9/5)+32 | tF = (TK×9/5)-459.67 | tF = (Tt×61461/125000)-459.67 |
| tC = (tF-32)×5/9 | tC | tC = TK-273.15 | tC = (Tt×6829/25000)-273.15 |
| TK = (tF+459.67)×5/9 | TK = tC+273.15 | TK | TK = Tt×6829/25000 |
| Tt = (tF+459.67)×125000/61461 | Tt = (tC+273.15)×25000/6829 | Tt = TK×25000/6829 | Tt |
Please let me know if this proposal makes sense to you.
Sincerely,
Stephen Clif Brown, PE