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: 4-76

Answer

$Q=94.49\ kJ$

Work Step by Step

Total energy balance: $Q-W_b=\Delta U$ For ideal gases: $PV=mRT$ In the initial state ($P_1=100\ kPa,\ T_1=296\ K,\ V_1=0.25\ m³,\ R=0.287\ kJ/kg.K$): Solving for the mass: $m = 0.294\ kg$ For the second state ($P_2=200\ kPa$): Solving for the temperature: $T_2=592\ K$ $W_{b,2-3} = P_2(V_3-V_2)=mR(T_3-T_2),\ W_b{1-2}=0\ (constant\ volume)$ $W_b=W_{b,2-3}=9.12\ kJ$ $\Delta U = mc_v(T_3-T_1)$ With $c_v=0.718\ kJ/kg.K$ $\Delta U=85.37\ kJ$ Hence, $Q=94.49\ kJ$
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