7. Special case of carbon dioxide CO2

CO ₂ entered the technical world a very long time ago, since it was first liquefied, then solidified, in the first third of the 19th century. Its use in compression refrigeration cycles, which began around 1866, remained very limited until recent years, when it has virtually disappeared. It has a number of disadvantages:

• its critical temperature (q _cr ) is low, +31.06°C; unlike other common refrigerants, conventional air or water chillers do not allow condensation;

• its triple point temperature (q _tr ) is relatively high, – 56.57°C. The temperature range (T _cr – T _tr ) in which the liquid...