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In an air motor cylinder the compressed air has an internal energy of 450 kJ/kg at the beginning of the expansion and an internal energy of 220 kJ/kg after expansion. If the work done by the air during the expansion is 120 kJ/kg, calculate the heat flow to and from the cylinder. |
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Answer» Internal energy at beginning of the expansion, u1 = 450 kJ/kg Internal energy after expansion, u2 = 220 kJ/kg Work done by the air during expansion, W = 120 kJ/kg Heat flow, Q : Using the relation, Q = (u2 – u1) + W ∴ Q = (220 – 450) + 120 = – 230 + 120 = – 110 kJ/kg Hence, heat rejected by air = 110 kJ/kg. |
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