Various Approaches to Thermodynamics

The paper surveys classical and recent approaches to thermodynamic analysis. Each approach is characterized by the type of questions asked and the types of results obtained. We conclude with a number of current challenges and open problems for thermodynamic analyses. THE CLASSICAL THERMODYNAMIC PARADIGMS The word thermodynamics conjures up a very definite subject in the minds of most scientists and engineers. Interestingly, the subjects it conjures up for a physicist, a chemist, a biologist, a mechanical engineer, and a chemical engineer have remarkably little overlap. Of course, all versions of the subject share the three laws and the associated constructs such as free energy, entropy, etc.. The basic cause of divergence is their focus on different systems of interest. The differences in thermodynamics as viewed by the different types of thermodynamicists become apparent by comparing the paradigm texts in standard use. The physics version of the subject is embodied in Callen's well-known text [1]. For the chemists, Lewis and Randall's classic text revised by Pitzer and Brewer [2] is the definitive treatment. We should also mention that both physics and chemistry curricula are steadily evolving toward more statistical mechanics based approaches which are displacing these classical paradigms. It is harder to point to a definitive text for biologists. Typically they begin with some training in the chemists' version of thermodynamics at the level of an undergraduate physical chemistry course, but then refine this to a currency driven picture of cellular processes which generate or consume ATP and other similar molecules that serve as the free energy currency for cellular processes. This picture was nicely developed in Lehninger's Bioenergetics [3] whose essential themes survive in modern biochemistry texts such as the one by Lehninger, Nelson, and Cox [4]. The paradigm among the mechanical engineering community i s probably best exemplified in Joseph Keenan's classic work [5]; modern texts elaborate further on the points that Keenan selected out as defining the mechanical engineers' topics of interest. Availability (exergy) is one such topic whose importance has grown considerably since Keenan resurrected it from Gibbs' original treatise [6]. Chemical engineers typically cut their thermodynamic teeth on the analyses presented in texts such as Smith [7]. Built upon these different paradigms comes a slew of contenders for new types of thermodynamics. This paper attempts to give an admittedly biased overview of a sample of these different approaches in response to a request from our chairman, Professor Ishida. We conclude with a list of modern challenges for thermodynamic analyses.