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 209: 4-143

Answer

$F=9,575\ kN$ $Q=-66.8\ kJ$

Work Step by Step

Initial state (saturated steam, 100 kPa) : $v_1=1.6941\ m³/kg,\ u_1=2505.6\ kJ/kg$ With the volume of 0.05m³: $m=0.02951\ kg$ Final state (saturated mixture, 30°C): $v_{2,L}=0.001004\ m³/kg,\ u_{2,L}=125.73\ kJ/kg,\ v_{2,G}=32.879\ m³/kg,\ u_{2,L}=2290.2\ kJ/kg$ $P_2=P_{sat}=4.2469\ kPa$ Given that $v_2=v_1$, because the piston is stuck: $x_2=\frac{v_2-v_{2,L}}{v_{2,G}}=0.05150$ Hence $u_2=u_{2,L}+x.u_{2,G}=243.67\ kJ/kg$ The friction force is given by: $F=-A\Delta P$ With an area of 0.1 m²: $F=9.575\ kN$ The heat transfer is given by the energy balance: $Q=\Delta U$ $Q=-66.8\ kJ$
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