Flow Nozzel Pressure Drop

[PhilOos]

Hi all,
I want to calculate the pressure drop over an ISA (short radius) flow nozzle. I've followed three different approaches to model the pressure drop, but all three delivered different answers.

I have a 250mm pipe, with a 191.76mm nozzle. The upstream pressure of the steam is 171 bar @ 540ºC, flowing at 126.7 kg/s.

If I follow the ISO 5167-3 code, I calculate a pressure drop of 9.5 bar.
If I apply isentropic expansion theory (in conjunction with the discharge coefficient used above) I calculate a pressure drop of 2.2 bar.
I have also calculated a K-loss factor from the discharged coefficient and applied it to K_loss*0.5*rho*Vel_nozzel^2. From this approach I've calculated a pressure drop of 1.2 bar.

Could anyone please give me some insight into this problem.

Regards


Philip Oosthuizen
Company info:
SteinMuller Engineering Services

http://www.steinmuller.co.za/

 

[rbcoulter]

http://www.eng-calcs.com/CFF0004.html

Get to the above online calculator and type in the word
"free" in the code box. You will need to convert your
units.

 

[CJKruger]

PhilOos, I assume you want the permanent dP. The calc is done as shown below. First term is to convert closeup pressure drop to permanent pressure drop. I just took a guess at the C and Y1 value, please check them.

dP = (1+0.014Beta?2.06Beta^2+1.18Beta^3) *W^2/rho1/(0.126447*K*Beta^2*D^2*Y1)^2

Beta = 191.76/250 = 0.767
W = 126.7*3600 = 456120 kg/h
rho1 = 51.78 kg/m3
K = 0.98/sqrt(1-Beta^4) = 1.21
D = 250 mm
Y1 = 0.99 (approx, from graphs)
dP = 0.331 * 130 kPa
= 43 kPa (permanent)

Groete
CKruger