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 9 - Gas Power Cycles - Problems - Page 540: 9-48

Answer

$T_{3}=1332 K$ $\dot{Q}_{\text {in }}=212\text{ kW}$

Work Step by Step

We begin by using the process types to fix the temperatures of the states. $$ \begin{aligned} & T_2=T_1\left(\frac{\boldsymbol{v}_1}{\boldsymbol{v}_2}\right)^{k-1}=T_1 r^{k-1}=(330 \mathrm{~K})(17)^{1.4-1}=1025 \mathrm{~K} \\ & T_3=T_2\left(\frac{v_3}{v_2}\right)=T_2 r_c=(1025 \mathrm{~K})(1.3)=1332 \mathrm{~K} \end{aligned} $$ Combining the first law as applied to the various processes with the process equations gives $$ \eta_{\mathrm{th}}=1-\frac{1}{r^{k-1}} \frac{r_c^k-1}{k\left(r_c-1\right)}=1-\frac{1}{17^{1.4-1}} \frac{1.3^{1.4}-1}{1.4(1.3-1)}=0.6597 $$ According to the definition of the thermal efficiency, $$ \dot{Q}_{\text {in }}=\frac{\dot{W}_{\text {est }}}{\eta_{\text {ti }}}=\frac{140 \mathrm{~kW}}{0.6597}=212 \mathrm{~kW} $$
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