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 202: 4-68

Answer

$Q=-69.57\ kJ$ $W_b=-250.25\ kJ$

Work Step by Step

For an ideal gas: $PV=mRT$ In the first state ($m=1kg, P_1=100kPa, T_1=25°C=298.15K, R=0.1889\ kJ/kg.K$): $V_1=0.563m³$ In the second state ($P_2=1000kPa, T_2=300°C=573.15K$): $V_2=0.108m³$ The boundary work in this case is given by: $W_b=\frac{1}{2}(P_1+P_2)(V_2-V_1)$ $W_b=-250.25\ kJ$ The energy balance for this system is: $Q-W_b=\Delta U $ $\Delta U = mc_v\Delta T$ With $c_v=0.657\ kJ/kg.K$ we get to: $\Delta U = 180.68\ kJ$ Hence $Q=-69.57\ kJ$
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