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 198: 4-31

Answer

$Q = 46.85\ kJ$

Work Step by Step

At the initial state (100°C, saturated, 12.3% quality), from steam tables: $v_{1,L} = 0.001043 m³/kg,\ v_{1,G} = 1.6720\ m³/kg$ $u_{1,L} = 419.06 kJ/kg,\ u_{1,G} = 2506.0\ kJ/kg$ $v_1=v_{1,L}+x_1(v_{1,G}-v_{1,L})$ $v_1 = 0.20657\ m³/kg$ Therefore, with a volume of 10L, the mass is: $m = 0.04841\ kg$ $u_1=u_{1,L}+x_1(u_{1,G}-u_{1,L})$ $u_1 = 675.76\ kJ/kg$ The process occurs at a constant volume, therefore, the final state is $T_2=150°C,\ v_2=v_1$: $v_{2,L} = 0.001091 m³/kg,\ v_{2,G} = 0.39248\ m³/kg$ $u_{2,L} = 631.66 kJ/kg,\ u_{2,G} = 2559.1\ kJ/kg$ $x_2 = \frac{(v_2-v_{1,L})}{(v_{1,G}-v_{1,L})}$ $x_2 = 0.525 $ $u_2 = 1643.54\ kJ/kg $ For a stationary, constant-volume, closed system: $Q = \Delta U$ $Q = 46.85\ kJ$
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