3. Air compressor is a single acting two cylinder unit which takes in an air vol

Question

3. Air compressor is a single acting two cylinder unit which takes in an air volume of 0.2 m3/s. The initial absolute pressure is .1 MPa. The final pressure is .7 MPa. Consider intermediate compression to be ideal and perfect intercooling. The compressor runs at 600 RPM. The index of compression is 1.25.

(a) Find the intermediate pressure
(b) The total volume of the cylinders
(c) Work done per cycle

Had this question on a 1st class power engineering thermal exam. A bit confused by what they are asking and how to set it up. I hope I wrote it out correctly.

Explanation / Answer

: Intake volume, v1=0.2m 3 /s Intake pressure, p1=0.1MPa Intake temperature,T1=16+273=289K Final pressure,p3=0.7MPa Compression index in both stages n1=n2=n=1.25 Speed of the compressor, N=600 r.p.m. Cp=1.005 kJ/kgK, R=0.287 kJ/kgK i. The intermediate pressure p2: ? ? 1 2' 2 1 2' 2 2 P ? P ? P ,P ? P ? P P2=0.2646 MPa ii. The total volume of each cylinder, vs1, vs2: We know that vs1 (Volume of L.P.cylinder)=0.02m 3 Also vs2 (Volume of H.P.cylinder)=0.00756m 3 iii. The power required to drive the compressor, P ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1 1 2 1 1 3 1 1 n n p p p V n n p = 42.96 kW

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