Question 6.42: Reconsider Prob. 6–41. Using EES (or other) software, invest......
Reconsider Prob. 6-41. Using EES (or other) software, investigate the effect of the inlet velocity on the exit velocity and the ratio of the inlet-to-exit area. Let the inlet velocity vary from 180 to 260 \mathrm{~m} / \mathrm{s}. Plot the final results against the inlet velocity, and discuss the results.
Problem 6-41 is reconsidered. The effect of the inlet velocity on the exit velocity and the ratio of the inlet-to-exit area as the inlet velocity varies from 180 \mathrm{~m} / \mathrm{s} to 260 \mathrm{~m} / \mathrm{s} is to be investigated. The final results are to be plotted against the inlet velocity.
Analysis The problem is solved using EES, and the solution is given below.
Function HCal(WorkFluid$, Tx, Px)
“Function to calculate the enthalpy of an ideal gas or real gas”
If ‘N2’ = WorkFluid$ then
HCal:=ENTHALPY(WorkFluid$,T=Tx) “Ideal gas equ.”
else
HCal:=ENTHALPY(WorkFluid$,T=Tx, P=Px)”Real gas equ.”
endif
end HCal
“System: control volume for the nozzle”
“Property relation: Nitrogen is an ideal gas”
“Process: Steady state, steady flow, adiabatic, no work”
“Knowns”
WorkFluid$ = ‘N2’
T[1] = 7 [C]
P[1] = 60 [kPa]
{Vel[1] = 200 [m/s]}
P[2] = 85 [kPa]
T[2] = 22 [C]
“Property Data – since the Enthalpy function has different parameters
for ideal gas and real fluids, a function was used to determine h.”
h[1]=HCal(WorkFluid$,T[1],P[1])
h[2]=HCal(WorkFluid$,T[2],P[2])
“The Volume function has the same form for an ideal gas as for a real fluid.”
v[1]=volume(workFluid$,T=T[1],p=P[1])
v[2]=volume(WorkFluid$,T=T[2],p=P[2])
“From the definition of mass flow rate, m_dot = A*Vel/v and conservation of mass the area ratio
A_Ratio = A_1/A_2 is:”
A_Ratio*Vel[1]/v[1] =Vel[2]/v[2]
“Conservation of Energy – SSSF energy balance”
h[1]+Vel[1]^2/(2*1000) = h[2]+Vel[2]^2/(2*1000)
