Basic concepts of energy converters

Thermal engines, whether reciprocating or continuous flow (e.g. turbojet engines and power station turbines), refrigeration-freezing machines and heat pumps are all energy converters whose scientific principles must be understood if their design and implementation are to be mastered. This article describes these principles and their applications.

As these scientific principles belong to the field of thermodynamics, the first part of this article is devoted to presenting the first and second principles of this science. It should be noted, however, that it is clearly oriented towards technical applications, with enthalpy and entropy balances in particular.

In the second part, we apply the principle of transferring energy, and the corresponding extensities, from high voltage to low voltage, as well as the principle of conservation of extensities, to define energy converters and show the need for their operation between at least four energy reservoirs, two for each of the two types of energy used in the converter. In view of this reservoir symmetry, these converters, which all have a driving and a generating part, could theoretically operate in reverse. However, since heat differs from other types of energy in that its extensive variable, entropy, is not conservative, monothermal thermal generators exist whose operation cannot be reversed. This general presentation of converters is followed by a definition and examination of the theoretical operation of Carnot converters, which are optimally efficient and still serve as a benchmark for real converters.

This search for the optimum, in line with the ongoing quest to save certain types of energy, can be carried out by entropy analyses of energy system operation. However, exergy analyses appear to be more practical for technical applications. That's why this article focuses, in fine, on the definition of exergy and its complement, anergy, as well as on their transfers and balances.