An ideal reheat Rankine cycle operates between the pressure limits of 20 kPa and 10 MPa, with reheat occurring at 3 MPa. The temperature of steam at the inlets of both turbines is 500°C, and the enthalpy of steam is 3027 kJ/kg at the exit of the high-pressure turbine, and 2385 kJ/kg at the exit of the low-pressure turbine. Disregarding the pump work, the cycle efficiency is
A)26%
B)32%
C)57%
D)40%
E)60%

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=20 "kPa"
P2=10000 "kPa"
P3=P2
P4=3000 "kPa"
P5=P4
P6=P1
T3=500 "C"
T5=500 "C"
s4=s3
s6=s5
h1=ENTHALPY(Steam_IAPWS,x=0,P=P1)
h2=h1
h44=3104 "kJ/kg - for checking given data"
h66=2385 "kJ/kg - for checking given data"
h3=ENTHALPY(Steam_IAPWS,T=T3,P=P3)
s3=ENTROPY(Steam_IAPWS,T=T3,P=P3)
h4=ENTHALPY(Steam_IAPWS,s=s4,P=P4)
h5=ENTHALPY(Steam_IAPWS,T=T5,P=P5)
s5=ENTROPY(Steam_IAPWS,T=T5,P=P5)
h6=ENTHALPY(Steam_IAPWS,s=s6,P=P6)
q_in=(h3-h2)+(h5-h4)
q_out=h6-h1
Eta_th=1-q_out/q_in
"Some Wrong Solutions with Common Mistakes:"
W1_Eff = q_out/q_in "Using wrong relation"
W2_Eff = 1-q_out/(h3-h2) "Disregarding heat input during reheat"
W3_Eff = 1-(T1+273)/(T3+273); T1=TEMPERATURE(Steam_IAPWS,x=0,P=P1) "Using Carnot efficiency"
W4_Eff = 1-q_out/(h5-h2) "Using wrong relation for q_in"

An Ideal Reheat Rankine Cycle Operates Between the Pressure Limits