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

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

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

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Compressors, Gas Turbines and Jet Engines
For a two stage reciprocating compressor, compression from p₁ to p₃ is with perfect intercooling and no pressure losses. If compression in both the cylinders follows the same polytropic process and the atmospheric pressure is pa, then the intermediate pressure p₂ is given by

p₂ = Pa p₃/p₁
p₂ = p₁. p₃
p₂ = (p₁ + p₃)/2
P₂ = Pa × p₃/p₁

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