Steam expands in an adiabatic turbine from 4 MPa and 500°C to 0.5 MPa and 250°C at a rate of 1740 kg/h. The power output of the turbine is
A)1004 kW
B)485 kW
C)182 kW
D)377 kW
E)235 kW

Question

Quizplus · Accepted Answer

Solved by EES Software. Solutions can be verified by copying-and-pasting the following lines on a blank EES screen. 
P1=4000 "kPa"
T1=500 "C"
P2=500 "kPa"
T2=250 "C"
m_dot=1740/3600 "kg/s"
Q_dot_loss=0 "kJ/s"
h1=ENTHALPY(Steam_IAPWS,T=T1,P=P1)
h2=ENTHALPY(Steam_IAPWS,T=T2,P=P2)
"The rate form of energy balance for a steady-flow system is E_dot_in = E_dot_out"
-W_dot_out-Q_dot_loss=m_dot*(h2-h1) 
"Some Wrong Solutions with Common Mistakes:"
-W1_Wout-Q_dot_loss=(h2-h1)/m_dot "Dividing by mass flow rate instead of multiplying"
-W2_Wout-Q_dot_loss=h2-h1 "Not considering mass flow rate"
u1=INTENERGY(Steam_IAPWS,T=T1,P=P1)
u2=INTENERGY(Steam_IAPWS,T=T2,P=P2)
-W3_Wout-Q_dot_loss=m_dot*(u2-u1) "Using internal energy instead of enthalpy"
-W4_Wout-Q_dot_loss=u2-u1 "Using internal energy and ignoring mass flow rate"

Steam Expands in an Adiabatic Turbine from 4 MPa and 500°C