Combustion gases with k = 1.34 enter a converging nozzle at stagnation temperature and pressure of 460°C and 780 kPa, and are discharged into the atmospheric air at 20°C and 100 kPa. The lowest pressure that will occur within the nozzle is
A)27 kPa
B)100 kPa
C)321 kPa
D)420 kPa
E)780 kPa

Question

Quizplus · Accepted Answer

Solved by EES Software. Solutions can be verified by copying-and-pasting the following lines on a blank EES screen. 
k=1.34
Po=780 "kPa"
Patm=100
"The critical pressure is"
P_throat=Po*(2/(k+1))^(k/(k-1))
"The lowest pressure that will occur in the nozzle is the higher of the critical or atmospheric pressure."
"Some Wrong Solutions with Common Mistakes:"
W1_Pthroat=Patm "Assuming constant pressure"
W2_Pthroat=Po*(1/(k+1))^(k/(k-1)) "Using wrong relation"
W3_Pthroat=100 "Assuming atmospheric pressure"

Combustion Gases with K = 1