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 3 - Properties of Pure Substances - Problems - Page 153: 3-36E

Answer

$T_{2}=104.7^{\circ}F$ $h_{2}=124.7\frac{Btu}{lbm}$

Work Step by Step

From table A-11E $P_{1}=9.869psia$ $\upsilon_{1}=\upsilon_{f}+x\upsilon_{fg}=0.01143\frac{ft^3}{lbm}+0.8*(4.4286\frac{ft^3}{lbm}-0.01143\frac{ft^3}{lbm})=3.5452\frac{ft^3}{lbm}$ Then: $V_{1}=m\upsilon_{1}=0.13lbm*3.5452\frac{ft^3}{lbm}=0.4609ft^3$ $V_{2}=1.5V_{1}=1.5*0.4609ft^3=0.6914ft^3$ To calculate the distance traveled by the piston: $A=\frac{\pi D^2}{4}=\frac{\pi*(1ft)^2}{4}=0.7854ft^2$ $\Delta x=\frac{\Delta V}{A}=\frac{0.6914ft^3-0.4609ft^3}{0.7854ft^2}=0.2935ft*\frac{12in}{1ft}=3.522in$ Then the change of pressure is: $A=\frac{\pi D^2}{4}=\frac{\pi*(12in)^2}{4}=113.1in^2$ $P=\frac{F}{A}=\frac{k\Delta x}{A}=\frac{37\frac{lbf}{in}*3.522in}{113.1in^2}=1.1522psia$ Now to calculate the final temperature and enthalpy: $P_{2}=P_{1}+\Delta P=9.869psia+1.1522psia=11.0212psia$ $\upsilon_{2}=\frac{V_{2}}{m}=\frac{0.6914ft^3}{0.13lbm}=5.3185\frac{ft^3}{lbm}$ As $\upsilon\gt \upsilon_{g}$ is a superheated vapor From EES: $T_{2}=104.7^{\circ}F$ $h_{2}=124.7\frac{Btu}{lbm}$
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