Compressors, Gas Turbines and Jet Engines
The overall efficiency of the compressed air system is the

Ratio of shaft input to the compressor to the shaft output of air motor
Product of shaft output of air motor and shaft input to the compressor
Ratio of shaft output of the air motor to the shaft input to the compressor
None of these

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Compressors, Gas Turbines and Jet Engines
If p₁, is the pressure of air entering the L.P. cylinder and p₂ is the pressure of air leaving the L.P. cylinder (or inter-cooler pressure), then the ratio of cylinder diameters for a single acting, two stage reciprocating air compressor with complete intercooling is given by (where D₁ = Dia. of L.P. cylinder, and D₂ = Dia. of H.P. cylinder)

D₁/D₂ = p₁ p₂
D₁/D₂ = p₁/p₂
None of these
D₁/D₂ = p₂/p₁

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Compressors, Gas Turbines and Jet Engines
The following is true for an open cycle gas turbine having exhaust heat exchanger. Atmospheric air before entering the compressor is

Compressed air before entering the combustion chamber is heated
Heated
Bled gas from turbine is heated and readmitted for complete expansion
Exhaust gases drive the compressor

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