Electric Motors and Turbines

A.  Efficiencies range from 85-95% for electric motors, 42-78% for steam turbines 28-38% for gas engines and turbines.
B.  For services under 75 kW (100 hp), electric motors are almost always used.  They can be used for services up to about 15000 kW (20000 hp)
C.  Turbines can be justified in services where they will yield several hundred horsepowers.  Otherwise, throttle valves are used to release pressure.
D.  A quick estimate of the energy available to a turbine is given by:

where:   Delta H = Actual available energy, Btu/lb
Cp = Heat Capacity at constant pressure, Btu/lb 0F
T1 = Inlet temperature, 0R
P1 = Inlet pressure, psia
P2 = Outlet pressure, psia
K = Cp/Cv