Thermodynamics: An Engineering Approach 8th Edition

Published by McGraw-Hill Education
ISBN 10: 0-07339-817-9
ISBN 13: 978-0-07339-817-4

Chapter 4 - Energy Analysis of Closed Systems - Problems - Page 199: 4-35

Answer

a) $T_2 = 605.7°C$ b) $W=45\ kJ$ c)$Q = 288.31\ kJ$

Work Step by Step

At the initial state (200 kPa, 200°C): $v_1=1.08049\ m³/kg,\ u_1=2654.6\ kJ/kg$ With an initial volume of 0.4 m³, the mass is: $m = 0.37\ kg$ Since the final volume is 0.6 m³: $v_2 = 1.6207\ m³/kg$ Therefore at the final state ($P_2=250\ kPa$): $T_2 = 605.7°C,\ u_2=3312.2\ kJ/kg$ a) $T_2 = 605.7°C$ b)The boundary work is the area under the trapezoid shape defined by $(P_1,V_1),(P_2,V_2)$: $W = (V_2-V_1)\frac{P_1+P_2}{2}$ $W=45\ kJ$ c)The energy balance for the stationary closed-system: $Q-W=\Delta U$ $Q = 288.31\ kJ$ On the P-v diagram, both the initial and final states are to the right of the saturation curve, connected by a straight line.
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