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

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)

Measured diameters

Orifice diameters

Usage of plates

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.

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).

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

Orifice diameters

Calculating the flowrate   C = 0.5959 + 0.03122.1 - 0.18408+0.00292.5 (106/ReD)0.75 +0.0900L14/(1-4)-0.0337L’23 where L1= L’2 = 25.4/D  = 1 – (0.41 + 0.354)p/(κ p1) p1  53 bar a

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

Correction on MTA: from 16/07/2007 to 15/07/2008 So qm,c/qm,o is 1.001958.

Correction factors: volume or energy

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