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Flow Nozzel Pressure Drop

Flow Nozzel Pressure Drop

Flow Nozzel Pressure Drop

(OP)
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 @ 540ÂșC, 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/

RE: Flow Nozzel Pressure Drop

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



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