Compressed air energy storage
Cylinder pressure p1 20 MPa
Ambient pressure p2 0.1 MPa
Cylinder volume v1 5 10-3 m3
Cylinder temperature T1 293 K
Specific heat capacity cp 1 kJ/(kg·K)
Specific heat capacity cv 0.713 kJ/(kg·K)
Gas constant R=cp-cv — kJ/(kg·K)
Isentropic coefficient k=cp/cv — -
mass weight m=p·V/(R·T) — kg
Isothermal expansion Adiabatic expansion
Expanded volume v2 — m3 — m3
Energy released W — kJ — kJ
Temperature T2 — K — K
Compared to batteries, compressed air is favorable because of a high energy density, low toxicity, fast filling at low cost and long service life. These issues make it technically challenging to design air engines for all kind of compressed air driven vehicles (http://en.wikipedia.org/wiki/Compressed-air_energy_storage).