Compression of air (a vapor or gas) creates heat; the air (a vapor or gas) is warmer after compression. Expansion removes heat (creates cold). If no extra heat is added, the air will be much colder after expansion. If the heat generated during compression can be stored and used during expansion, the efficiency of the storage improves considerably. There are three ways in which a CAES system can deal with the heat. Air storage can be adiabatic, diabatic, or isothermal. Wikipedia, compressed air energy storage
See Also
Cold
Compression
compression-expansion pump
cycle of appearance and disappearance of mass
cycle of motion
Expansion
Flash Evaporation
Flash Steam
Heat
low-pressure cold areas of the evacuated fields
Steam
5.8.5 - The complete Contraction Expansion Cycle is as follows
12.30 - Thermal Radiation and Thermal Vacuum or Cold