Refrigeration

The man can for a very long time produce heat necessary to his activities. To produce cold is, on the other hand, a relatively recent technique, on a historical scale.

One knew as of the time of the Romans, to preserve the winter cold in the form of snow or of ice stored in underground shelters isolated using straw or of hay. What made it possible to refresh drinks and the mets with most extremely of the summer. It was also known that one could obtain lower temperatures by mixing crushed ice and sea salt.

The production itself of cold goes back only to the XIXe century, with the advance of knowledge as regards Thermodynamique and of electricity. We can underline besides, that the " term; to make froid" is not, physically speaking, exact. Because the principle is to withdraw existing heat in a medium and not to inject cold in this medium (to withdraw heat thus involves a cooling)

One can implement several principles:

- the absorption of a gas by a liquid is an endothermic phenomenon: it is using ammonia and of water that the first refrigerating machines were produced (“apparatus Carré”, before 1860, diagram opposite). This system exists still nowadays in small refrigerators without moving parts, for example for the camp-site.

- the evaporation of a liquid is also an endothermic phenomenon: it is this principle which is at the base, today, of the majority of the cold stores. A refrigerant at low boiling point undergoes a cycle of transformations: compression, cooling, relaxation, warming which makes it possible to make migrate the calories of the evaporator towards the condenser. This cycle is in fact the reverse of that of a thermal engine.

- the Réfrigération passivates by radiation: it is the permanent radiation of any body which causes the fall of temperature in the condition of being insulated suitably and had way such as the radiation can “flee” towards space.

The Peltier effect, in electricity, makes it possible to produce cold, but with a very weak output which holds it for particular applications where above the processes cannot be implemented.

See too

  • Froid
  • Réfrigérateur
  • Congélateur
  • Réfrigération passivates by radiation
  • Froid industrialist

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