In science, thermodynamicists (generations) refers to the grouping, ranking or categorization of thermodynamicists by their respective generational distance from French physicist Sadi Carnot. This ranking logic comes from American physics historian and chemist William Cropper, who defines Gibbs as the “principle third generation thermodynamicist”, and eludes to the idea that Clausius and Thomson were the principle second generation thermodynamicists, with Carnot being first generation or initiator of the "Carnot legacy". This gives 22 years per thermodynamic generation, based on the average distance between Carnot (b.1796), Clausius (b.1822), and Gibbs (b.1839). This scheme is discussed in the following quote: [7]

“Thomson touched on every one of the major problems of thermodynamics. But except for his temperature scale and interpretation of the energy concept, his work is not found in today’s textbook version of thermodynamics. Although he ranks with Clausius and Gibbs among thermodynamicists, his legacy is more limited than theirs. The comparison with Clausius is striking. These two, of about the same age, and both in possession of the Carnot legacy, had the same thermodynamic concerns. Yet it was the Clausius thermodynamic scheme, based on the two concepts of energy and entropy and their laws, that impressed Gibbs, the principle third generation thermodynamicist. Clausius cold also be obscure, but he left no doubt about the conceptual foundations of his theories, and he gave Gibbs the requisite clues to put together the scheme we see today in thermodynamics texts.”

On this Carnot-Clausius-Gibbs three-generation logic, which seems cogent, the following "generational table of principle thermodynamicists" is ordered by date of publication of works, showing the "principle" thermodynamicist of each generation (neglecting gas law pioneers, affinity chemist pioneers, heat engine developers, mathematics pioneers, etc). In this grouping scheme, we note, based on the same generation occurrence of C.G. Darwin's statistical "human thermodynamics" and Mehdi Bazargan's "thermodynamics of man", that human thermodynamics can be considered a fifth generation branch of thermodynamics.

Pre-generational thermodynamicists

1. Herman Boerhaave (1620) 2. Joseph Black (1761) 3.Antoine Lavoisier (1787) 4. Benjamin Thompson (1798) 5. Humphry Davy (1799) 6. Johann Goethe (1809) 7. Joseph Fourier (1811) 8. Gustave Coriolis (1829)

First generation thermodynamicists	Second generation thermodynamicists	Third generation thermodynamicists
1. Sadi Carnot (1824) 2. Emile Clapeyron (1834)	1. Germain Hess (1840) 2. Robert Mayer (1841) 3. James Joule (1843) 4. Hermann Helmholtz (1847-1882) 5. William Thomson (1849-1854) 6. William Rankine (1850-1859) 7. Rudolf Clausius (1850-1865) 8. Gustave Hirn (1856) 9. James Maxwell (1857-1871) 10. Peter Tait (1868) 11. (add) 12. etc.	1. August Horstmann (1868-1873) 2. Ludwig Boltzmann (1872-1895) 3. Willard Gibbs (1873-1901) 4. Jacobus van’ Hoff (1884) 5. Wilhelm Ostwald 6. (add) 7. etc.

Fourth generation thermodynamicists	Fifth generation thermodynamicists	Sixth generation thermodynamicists
1. Leon Winiarski (1890-1894) 2. Walther Nernst (1893-1906) 3. Max Planck (1897-1900) 4. Fritz Haber (1905) 5. Albert Einstein (1902-1907) 6. Otto Sackur (1908-1912) 7. (add) 8. etc.	1. Percy Bridgman (1914-1941) 2. Ralph Fowler (1922-1939) 3. C.G. Darwin (1922-1952) 4. James Partington (1913-1924) 5. Theophile De Donder (1922) 6. Gilbert Lewis (1923) 7. Merle Randall (1912-1942) 8. John Butler (1928-1935) 9. Edward Guggenheim (1933-1949) 11. Mehdi Bazargan (1935-1979) 10. Paul Epstein (1937) 11. (add) 12. etc.	1. Fritz Lipmann (1941) 2. Joseph Keenan (1941-1952) 3. Mark Zemansky (1943) 4. Erwin Schrodinger (1944-1946) 5. Samuel Glasstone (1947) 6. Ilya Prigogine (1947-1998) 7. Edward Obert (1948) 8. Frederick Rossini (1950) 9. etc

Seventh generation thermodynamicists	Eighth generation thermodynamicists	Ninth generation thermodynamicists
1. Hendrick van Ness (1959-2005) 2. Herbert Callen (1960-1985) 3. Raymond Kern (1964) 4. Alain Weisbrod (1964) 5. George Hatsopoulos (1965) 6. Laszlo Tisza (1966) 7. Joseph Kestin (1966) 8. Stephen Hawking (1970) 9. Jacob Bekenstein (1972) 10. Stanley Sandler (1977-2006) 11. Georgi Gladyshev (1977-2009+) 12. (add) 13. etc.	1. Donald Haynie (1993-2008+) 2. Gregor Anderson (1996) 3. Enrico di Cera (1995-2000) 4. Libb Thims (1995-2010+) 5. (add) 6. etc.	(2013 +/- 11 years)? 1. (add) 2. etc.

Notes
The 22-year per generation figure agrees calculated via the average distance between the birth of Carnot and the birth of Gibbs agrees with the 22-years per generation found when the table was first built intuitively, based on groupings as to who built on who's work, later finding a twenty-two year gaping between the eight generations.

References
1. Cropper, William H. (2001). Great Physicists: the Life and Times of the Leading Physicists from Galileo to Hawking (pg. 90). Oxford University Press.