General principles - the theory of refrigerating machines

Providing a body or environment with cold means extracting heat from it, which results in a lowering of its temperature and, very often, in changes of state: condensation, solidification, etc. These are the effects of cold which, in their great diversity, are at the service of modern man. It is these effects of cold, in all their diversity, that are at the service of modern man. Refrigeration machines extract heat from the media to be cooled. They discharge this heat, along with the thermal equivalent of the energy received, at a higher temperature, into the surrounding environment. These machines can also be used as heating systems. While the cold they produce is generally useless (heat is simply extracted from a medium where it is free - air, water or an industrial process), it is the heat rejected at a higher temperature that is used. This is what is commonly referred to as a heat pump, whose operating principles, and often technology, are similar to those of refrigeration machines.

Although there is a wide variety of cold production methods, some stand out from the rest in certain temperature ranges. For example, cycles based on the compression of liquefiable vapors (refrigerants) are gaining in importance in the very low-temperature range (cryogenics), and exercise almost absolute domination in temperature ranges down to around – 80°C for refrigeration machines, and up to around +100°C for heat pumps, leaving very little room for other cold production methods such as absorption, adsorption or thermodynamic gas cycles.

Like most economically important refrigeration applications, air conditioning for comfort (air conditioning) or industry, and the production, preservation and distribution of perishable foodstuffs belong to the field of compression cycles. The importance of these cycles is considerable. The overwhelming primacy of compression refrigeration machines is primarily due to their simplicity and efficiency. But it's also due to the sheer diversity of their components (compressors, heat exchangers, control units, refrigerants, etc.), which can be used in the smallest machines as well as the largest, and which are available almost everywhere in the world, generally mass-produced at very competitive prices. This makes it possible to assemble any type of compression cycle on demand.

A good knowledge of compression refrigeration cycles is therefore of major importance, which justifies the development reserved for them. This dossier [BE 9 730] provides general information on refrigeration systems. In the following