Speaker
Description
Thermodynamics has always been a fundamental and necessary discipline in support of fluid dynamics. In subsonic and (moderately) supersonic flows, the thermodynamic description of the fluid is relatively simple and can be accomplished at macroscopic, phenomenological level. Things complicate when energy densities in the flow field increase, as in aerothermodynamics. Nonequilibrium processes appear and the physical modeling requires a more incisive thermodynamic description whose understanding’s quest goes deeper into the microscopic layer of the physics at hand. In order to gain that understanding, we must be prepared to zoom in at molecular-structure level and to acquire sufficient knowledge of the necessary elements of quantum mechanics. In general, our thermodynamics-description strategy is based on perfect-gas mixtures whose molecules are thought to be in quantum-mechanical stationary states before and after collisions and/or interactions with fields. Accordingly, we introduce the concept of “quantum-state population distribution” and then we either follow a multi-temperature approach (Boltzmann population distributions) or a state-to-state approach (non-Boltzmann population distributions) to characterize the nonequilibrium dynamics of the physicochemical processes taking place in the fluid. The idea behind this practice seems so natural and, above all, so quantum-mechanically consistent that we take it for granted and we proceed to apply it without hesitation. But, does quantum mechanics really teach that this is the right thing to do? How does the concept “population distribution” arise within a quantum-mechanical context? This presentation attempts to find answers to these questions. The pursuit of the answers necessarily drags on stage also the controversy regarding the separation of molecular degrees of freedom, a still frequently debated theme regarding which the author pointed out some misunderstood aspects a few years ago [1].
[1] Domenico Giordano, “Impact of the Born-Oppenheimer Approximation on Aerothermodynamics”, Journal of Thermophysics and Heat Transfer, Vol. 21, No. 3, 647-657, July-September 2007
Summary
see abstract
