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: 4-72

Answer

$W_b=-149.99\ kJ$ $Q=-37.35\ kJ$

Work Step by Step

For a polytropic process: $TV^{n-1}=constant$ $T_1V_1^{n-1}=T_2V_2^{n-1}$ $T_2=T_1(\frac{V_1}{V_2})^{n-1}$ With $T_1=25°C=298.15K, V_1/V_2=2, n=1.3$ we get to: $T_2=367.06\ K$ The boundary work is given by: $W_b=\frac{mR}{1-n}(T_2-T_1)$ With $m=2.2kg, R=0.2968 kJ/kg.K$ $W_b=-149.99\ kJ$ The energy balance for this system results in: $Q-W_b=\Delta U=mc_v\Delta T$ With $c_v=0.743\ kJ/kg.K$: $\Delta U=112.64\ kJ$ $Q=-37.35\ kJ$
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