1. Assessment of error due to orifice diameter mis-measurement
Michael Reader-Harris
TUV NEL
Scotland

2. Introduction Orifice diameters have been mis-measured
The aim of this project was to calculate the error
Actual calculations have been carried out for Blackrod (2 orifice runs)

3. Measured diameters

4. Orifice diameters

5. Usage of plates

6. Why not simply recalculate?
The data supplied only give time to the nearest minute.
The size of the files (one as large as 69 MB) makes them difficult to analyse.

7. Calculating the flowrate
The mass flowrate qm is given by
where d is the throat diameter, C is the discharge coefficient,  is the expansibility,  is the density, p is the differential pressure, and  is the diameter ratio (=d/D).

8. Calculating the flowrate
If the corrected and original data are described with subscripts c and o, then the following correction factor is obtained:

9. Orifice diameters

10. Calculating the flowrate
C =   2.5 (106/ReD)0.75
L14/(1-4) L’23 where L1= L’2 = 25.4/D
 = 1 – ( 4)p/(κ p1) p1  53 bar a

11. Calculating the flowrate
C = C(ReD, , D)  =  (, p, p1, ) p1  53 bar a
ReD = 4qm/(π1D)
Consider a low flowrate condition:
p = 10 mbar: ReD= 3  106
and a high flowrate condition:
p = 500 mbar: ReD= 2  107

12. Correction on MTA: from 16/07/2007 to 15/07/2008
So qm,c/qm,o is

13. Correction factors: volume or energy

14. Results
The results have been analysed for Blackrod, but a similar calculation will work for any site