Orifice sizing clarification

[tractable09]

I am new to orifice sizing.
I am verifying the data from our contractor who sized a flow orifice on a medium pressure (43 bar) steam line to a turbine.Following data is available.
Full range flow = 10000 kg/hr
Operating flow = 5000 kg/hr
Opt. temp = 371 C
Opt press = 43 kg/cm2
Density (Ro) = 15.26 kg/m3

Contractor has provided the following results:
Orifice dia = 72.77 mm
Press drop max = 113.5 in H2O
Press drop opt. = 28.37 in H2O
Reynolds no. = 494253
Discharge coeff = 0.6

I tried to validate the data by using eq. to back calculate the flow rate:
q = CA sq.root(2DP/Ro)
q = m3/s
A = m2
DP = bar
Ro = kg/m3
C=0.6
But the results are far from matching, it comes out 22.2 kg/hr. Please guide for the right equation or anything I am doing wrong, thanks.

 

[casflo]

The flow is steam, so you must use in the equation the expansion factor, Y, and also take into account that the discharge coefficient, C, depends of the ratio between orifice diameter and pipe internal diameter.
Look at the Crane Technical Paper No 410.
Regards.
casflo

 

[CJKruger]

If you provide the pipe ID, others can double check the results. Order of magnitude the vendor results seem correct.

I prefer the equation in mass flow units, which is:
W = 0.0125217 K d^2 Y1 (Den1 hw)^0.5
W = kg/h
K = C/(1-Beta^4)^0.5
C = roughly 0.61
d = orifice bore, mm
Den1 = inlet density, kg/m3
hw = pres drop, mmH2O, at same tap location as C and Y
Y1 = gas expansion factor
= 1 ? (0.41 + 0.35 Beta^4) dP/P1/k for close-up taps
k = Cp/Cv

Cilliers

http://www.korf.co.uk

 

[tractable09]

Do I need to use expansion factor? As Press drop/Inlet press= 0.004, and this gives Y~1.
I've taken above equation from crane papers.
Pipe ID=6 in.
CJKRuger, can you cross check?
Regards,