Q8. A single stage, single acting reciprocating air compressor is to be replaced with a two-stage single acting machine.
The two-stage machine is designed for minimum work and has perfect intercooling.
The following conditions apply to both machines:
The suction conditions are 0.9 bar and 25℃.
The delivery pressure is 22.5 bar.
The index of compression in all the stages is 1.25.
The free air delivery is 0.07 m3/s at a pressure of 1.01325 bar and temperature of 15℃.
The clearance volume in both machines may be ignored.
(a) Sketch the two-stage cycle on a pressure- Volume diagram showing the work saved by intercooling and the isothermal compression curve. (3)
(b)Calculate EACH of the following.
(i) The indicated power of the two-stage machine; (4)
(ii) The power saved by using the two-stage machine: (2)
(iii) The percentage reduction in the discharge temperature using the two-stage machine. (4)
(iv) The isothermal efficiency of the two-stage machine. (3)
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