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 5 - Mass and Energy Analysis of Control Volumes - Problems - Page 265: 5-132

Answer

a) $T_2=261.7°C$ b) $m_i=0.0176\ kg$

Work Step by Step

From tables A-4 to A-6: Initial ($P_1=0.5\ MPa, T_1=200°C$): $v_1=0.42503\ m³/kg,\ u_1=2643.3\ kJ/kg$ Inlet ($P_i=1\ MPa, T_2=350°C$): $h_i=3158.2\ kJ/kg$ $m=V/v$ Initial $V_1=0.01\ m³$: $m_1=0.0235\ kg$ Final $V_2=0.02\ m³$: $m_2=0.02/v_2$ From the material balance: $m_i=m_2-m_1$ From the energy balance: $-W_{b,e}+m_ih_i=m_2u_2-m_1u_1$ Since $W_b=-P(V_2-V_1)=5\ kJ$ $-W_b+m_ih_i=m_2u_2-m_1u_1$ $m_2(h_i-u_2)=m_1(h_i-u_1)+5$ By trial and error: $T_2=261.7°C,\ v_2=0.4858\ m³/kg,\ u_2=2742.4\ kJ/kg$ Hence the final mass is: $m_2=0.0412\ kg$ $m_i=0.0176\ kg$
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