In science, thermodynamicists (generations) refers to the grouping, ranking or categorization of thermodynamicists by their respective generational distance from French physicist Sadi Carnot (first generation) to Willard Gibbs (third generation), to modern times (ninth generation), according to the 1991 generation scheme enunciated by American science historian William Cropper, as outlined below—those with dates bolded being human thermodynamics connected theorists:
Thermodynamicist Generation Groupings
Maxwell | Generation scheme
In 1878, Irish physicist James Maxwell summarized the learning of the definition of entropy as follows:
“By the introduction of the expression, “without compensation” (verses “of itself”), combined with a full interpretation of this phrase, the statement of the second principle (“that heat cannot without compensation pass from a colder to a warmer body”) becomes complete and exact; but in order to understand it we must have a previous knowledge of the theory of transformation-equivalents, or in other words entropy, and it is to be feared that we shall have to be taught thermodynamics for several generations before we can expect beginners to receive as axiomatic the theory of entropy.”
Cropper | Generation scheme
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: 
“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
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.
The following are related quotes:
“Rossini was one of the preeminent thermodynamicists of the twentieth century.”
— Ernest Eliel (1999), Biographical Memoirs, National Academies of Press 
1. Cropper, William H. (2001). Great Physicists: the Life and Times of the Leading Physicists from Galileo to Hawking (pg. 90). Oxford University Press.
2. (a) Eliel, Ernest L. (1999). “Frederick Rossini”, Biographical Memoirs (Priestley Medal address, pg. 294). National Academy of Sciences.
(b) Ernest L. Eliel – Wikipedia.