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Q20. The free air capacity of a reciprocating air compressor is 15 m³/min. Free air and suction pressure and temperature are 1 bar and 27°C respectively. The delivery pressure is 9 bar. Compression is carried out in two stages with perfect intercooling. The stage pressure ratios are equal. The index of compression and expansion is 1.28.

(a) Sketch the p-V diagram for the compressor. (3)

(b) Determine EACH of the following:

(i) The total indicated power; (6)

(ii) The rate of intercooling; (3)

(iii) The isothermal efficiency. (4)

Note:  For air, R = 0.287 kJ/kg K and C_p = 1.005 kJ/kg K.