fSteam expands in a turbine from 6 MPa and 500°C to 0.2 MPa and 150°C at a rate of 1.2 kg/s. Heat is lost from the turbine at a rate of 34 kJ/s during the process. The power output of the turbine is
A)750 kW
B)784 kW
C)818 kW
D)573 kW
E)641 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. 
T1=500 "C"
P1=6000 "kPa"
T2=150 "C"
P2=200 "kPa"
m_dot=1.2 "kg/s"
Q_dot_loss=34 "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*(h1-h2) 
"Some Wrong Solutions with Common Mistakes:"
W1_Wout=m_dot*(h1-h2) "Disregarding heat loss"
W2_Wout-Q_dot_loss=m_dot*(h1-h2) "Assuming heat gain instead of loss"
u1=INTENERGY(Steam_IAPWS,T=T1,P=P1)
u2=INTENERGY(Steam_IAPWS,T=T2,P=P2)
W3_Wout+Q_dot_loss=m_dot*(u1-u2) "Using internal energy instead of enthalpy"
W4_Wout-Q_dot_loss=m_dot*(u1-u2) "Using internal energy and wrong direction for heat"

FSteam Expands in a Turbine from 6 MPa and 500°C