Towards the meaningful learning of thermodynamics: A proposal for teaching exergy.

Thermodynamics studies the nature of energy and its forms of existence and transmission between systems. Exergy, as part of the Thermodynamics program in Chemical Engineering, plays a fundamental role in the development and promotion of processes related to energy saving. However, an analysis of the programs of Thermodynamics and related subjects for the Chemical Engineering degree in many Argentine universities revealed that there are few programs that include exergy as a component part of a Thermodynamics taught course, and those that do often use the few textbooks that address the subject. In this sense, a total of 92 textbooks have been counted as bibliography for the teaching of Thermodynamics/Physical Chemistry in Chemical Engineering. Out of that total, 39 books appear in at least two course programs, while the remaining 53 are less known books, and are cited by only one program. Of the 39 most widely used books, only 14 include the topic of exergy. On the other hand, the statistics of grades obtained by students in Thermodynamics indicate a low performance in the understanding of exergy. The results of exams showed deficiencies in different theoretical aspects related to the understanding of the topic with percentages of failure of 60%, 47% and 21% in three different evaluation instances. Moreover, the total percentage of students who could not solve the exergy problems or solved it with errors was significantly higher (> 67%) than the percentage of those who managed to solve it correctly (< 20%). In this work, a pedagogical proposal for the teaching of Exergy was formulated, contemplating the learning axes of the theoretical framework, the language and the nature of Thermodynamics. It is intended that this proposal serves teachers to promote a meaningful learning of exergy for Chemical Engineering students. • The multiplicity of historical definitions of exergy were discussed. • A proposal for teaching exergy is presented based on the meaningful learning theory. • A new procedure for deriving exergy expressions of closed and open systems was developed. • Differences between lost work, irreversibility and destroyed exergy were discussed. • Exergetic efficiencies for process equipment were defined and calculated. [ABSTRACT FROM AUTHOR]