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 681: 12-32

Answer

$β_{}=0.00381\ K^{-1}$ $α_{}=0.00482\ K^{-1}$

Work Step by Step

The volume expansivity and isothermal compressibility are expressed as $$ \beta=\frac{1}{v}\left(\frac{\partial v}{\partial T}\right)_P \text { and } \alpha=-\frac{1}{v}\left(\frac{\partial v}{\partial P}\right)_T $$ Approximating differentials by differences about the specified state, $$ \begin{aligned} \beta & \cong \frac{1}{v}\left(\frac{\Delta v}{\Delta T}\right)_{P=200 \mathrm{kPa}}=\frac{1}{v}\left(\frac{\boldsymbol{v}_{40^{\circ} \mathrm{C}}-\boldsymbol{v}_{20^{\circ} \mathrm{C}}}{(40-20)^{\circ} \mathrm{C}}\right)_{P=200 \mathrm{kPa}} \\ & =\frac{1}{0.11874 \mathrm{~m}^3 / \mathrm{kg}}\left(\frac{(0.12322-0.11418) \mathrm{m}^3 / \mathrm{kg}}{20 \mathrm{~K}}\right) \\ & =\mathbf{0 . 0 0 3 8 1\ \mathrm { K } ^ { - 1 }} \end{aligned} $$ and $$ \begin{aligned} \alpha & \cong-\frac{1}{v}\left(\frac{\Delta v}{\Delta P}\right)_{T=30^{\circ} \mathrm{C}}=-\frac{1}{v}\left(\frac{v_{240 \mathrm{ka}}-v_{180 \mathrm{kPa}}}{(240-180) \mathrm{kPa}}\right)_{T=30^{\circ} \mathrm{C}} \\ & =-\frac{1}{0.11874 \mathrm{~m}^3 / \mathrm{kg}}\left(\frac{(0.09812-0.13248) \mathrm{m}^3 / \mathrm{kg}}{60 \mathrm{kPa}}\right) \\ & =\mathbf{0 . 0 0 4 8 2}\ \mathbf{k P a}^{-1} \end{aligned} $$
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