Question 8.180E: A compressor is used to bring saturated water vapor at 103 l...

A compressor is used to bring saturated water vapor at 103 lbf / in ^{2} up to 2000 lbf / in ^{2}, where the actual exit temperature is 1200 F. Find the irreversibility and the second law efficiency.

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Inlet state: Table F.7.1      h _{ i }=1188.4   Btu / lbm ,      s _{ i }=1.601   Btu / lbm  R

Actual compressor F.7.2:      h _{ e }=1598.6   Btu / lbm ,      s _{ e }=1.6398   Btu / lbm  R

Energy Eq. actual compressor:      – w _{ c , ac }= h _{ e }- h _{ i }=410.2   Btu / lbm

Eq.8.13:          i = T _{0}\left( s _{ e }- s _{ i }\right)=536.67 \times(1.6398-1.601)= 2 0 . 8 2   Btu / lbm

Eq.8.15:          w _{ rev }= i + w _{ c , ac }=20.82+(-410.2)=-389.4   Btu / lbm

\eta_{I I}=- w _{ rev } /\left(- w _{ c , ac }\right)=389.4 / 410.2= 0 . 9 4 9

 

………………………………………..

Eq.8.13 : \dot{I}=\dot{W}^{ rev }-\dot{W}_{ c.v.ac }=\dot{Q}_{0}^{ rev }=T_{0} \dot{S}_{\text {gen ac }}

Eq.8.15 :
\begin{aligned}i &=\dot{I} / \dot{m}=w^{ rev }-w_{ c.v.  ac }=q_{0}^{ rev }=T_{0} S_{ gen  ac } \\&=T_{0}\left[s_{e}-s_{i}-\sum \frac{q_{j}}{T_{j}}\right]\end{aligned}

 

 

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