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 12 - Thermodynamic Property Relations - Problems - Page 684: 12-91

Answer

$\frac{v_2}{v_1}=1.0104 $

Work Step by Step

We take $\nu=v(P, T)$. Its total differential is $$ d v=\left(\frac{\partial v}{\partial T}\right)_P d T+\left(\frac{\partial v}{\partial P}\right)_T d P $$ which, for a constant pressure process, reduces to $$ d v=\left(\frac{\partial v}{\partial T}\right)_P d T $$ Dividing by $v$ and using the definition of $\beta$, $$ \frac{d v}{v}=\frac{1}{v}\left(\frac{\partial v}{\partial T}\right)_P d T=\beta d T $$ Taking $\beta$ to be a constant, integration from 1 to 2 yields $$ \ln \frac{v_2}{v_1}=\beta\left(T_2-T_1\right) $$ or $$ \frac{v_2}{v_1}=\exp \left[\beta\left(T_2-T_1\right)\right] $$ The average value of $\beta$ is $$ \beta_{\mathrm{me}}=\left(\beta_1+\beta_2\right) / 2=\left(49.2 \times 10^{-6}+54.2 \times 10^{-6}\right) / 2=51.7 \times 10^{-6} \mathrm{~K}^{-1} $$ Substituting the given values, $$ \frac{v_2}{v_1}=\exp \left[\beta\left(T_2-T_1\right)\right]=\exp \left[\left(51.7 \times 10^{-6} \mathrm{~K}^{-1}\right)(500-300) \mathrm{K}\right]=1.0104 $$ Therefore, the volume of copper block will increase by 1.04 percent.
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