Hot combustion gases (assumed to have the properties of air at room temperature) enter a gas turbine at 0.8 MPa and 1500 K at a rate of 2.1 kg/s, and exit at 0.1 MPa and 800 K. If heat is lost from the turbine to the surroundings at a rate of 150 kJ/s, the power output of the gas turbine is
A)1477 kW
B)1677 kW
C)1327 kW
D)1124 kW
E)872 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. 
Cp_air=1.005 "kJ/kg-C"
P1=800 "kPa"
T1=1500 "K"
T2=800 "K"
m_dot=2.1 "kg/s"
Q_dot_loss=150 "kJ/s"
"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*Cp_air*(T1-T2)
"Alternative: Variable specific heats - using EES data"
W_dot_outvariable+Q_dot_loss=m_dot*(ENTHALPY(Air,T=T1)-ENTHALPY(Air,T=T2))
"Some Wrong Solutions with Common Mistakes:"
W1_Wout=m_dot*Cp_air*(T1-T2) "Disregarding heat loss"
W2_Wout-Q_dot_loss=m_dot*Cp_air*(T1-T2) "Assuming heat gain instead of loss"

Hot Combustion Gases (Assumed to Have the Properties of Air