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A heavily insulated cylinder/piston contains ammonia at 60°C, 1200 kPa. The piston is moved, expanding the ammonia in a reversible process until the temperature is −20°C during which 600 kJ of work is given out by ammonia. What was the initial volume of the cylinder?

A heavily insulated cylinder/piston contains ammonia at 60°C, 1200 kPa. The piston is moved, expanding the ammonia in a reversible process until the temperature is −20°C during which 600 kJ of work is given out by ammonia. What was the initial volume of the cylinder? Correct Answer 0.385 m3

State 1: v1 = 0.1238 m3/kg, s1 = 5.2357 kJ/kg K, u1 = h – Pv = 1553.3 – 1200×0.1238 = 1404.9 kJ/kg Process: reversible (1S2(gen) = 0) and adiabatic (dQ = 0) => s2 = s1 State 2: T2, s2 ⇒ x2 = (5.2357 – 0.3657)/5.2498 = 0.928 u2 = 88.76 + 0.928×1210.7 = 1211.95 kJ/kg 1Q2 = 0 = m(u2 – u1) + 1W2 = m(1211.95 – 1404.9) + 600 ⇒ m = 3.110 kg V1 = mv1 = 3.11 × 0.1238 = 0.385 m3.

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