Thermomechanical generator. Refrigerators and heat pumps

This article follows on from [BE 8 064] . It is specific to generators that convert mechanical (or electrical) energy into thermal energy to produce heat or cold. Consequently, this first article will be referred to if necessary. In the first case, we are dealing with refrigerators; in the second, with heat pumps.

However, before dealing directly with these machines, it's worth adding to our general knowledge of the fluids used as thermodynamic (i.e. working) fluids, in their three forms: gaseous, liquid and two-phase liquid-vapor. Basic information on the physics of these fluids is given first, before presenting the energies involved in their compression or expansion. In all cases, it is essential to know the basic expressions for variations in the state functions of these fluids. This is why, at the very beginning of the article, we present various expressions for heat exchange between a system and its environment.

As the aim of this article is not to provide constructive elements for thermomechanical generators, its presentation is limited to general and theoretical aspects, i.e. operating principles, whether for machines operating strictly with a gas (generally air) or for the much more common machines using a fluid in its three states, referred to as refrigerant vapor machines.

As in the case of the general article on energy converters, the last part of this article provides elements for applying exergy theory to generators.