### Size a Liquid Orifice Meter with ISO 5167 and Excel

This Excel spreadsheet sizes a liquid orifice meter using the equations in ISO 5167.  Orifice meters determine liquid flowrate by measuring the pressure difference across a constriction in a pipe.

The spreadsheet is free - all I ask is that you credit this website with its authorship (and perhaps provide a link!)

The equations given in ISO 5167 are given below.
• C is the discharge coefficient (the equation is only valid for the three standard tap positions defined below)
• Re is the Reynolds number
• L1 and L2 are the upstream and downstream tap positions (ft)
• P1 and P2 are the upstream and downstream pressures (psig)
• D1 and D2 are the pipe and orifice diameters (inches)
• V is the liquid velocity in the pipe (ft s-1)
• ρ is the liquid density slugs ft-3
• μ is the liquid viscosity lb-sec ft-2

ISO 5167 defines three different tap positions for the pressure probes (Corner, D-D/2 and Flange taps). These positions the values of L1 and L2, and are given below

• Corner Taps: L1 = L2 = 0
• Flange Taps: L1 = L2 = 1 inch
• D-D/2 Taps: L1 = D1, L2 = D1/2
The solution to the equations is iterative; you need Re to calculate C, but you need Q to calculate Re, but you need C to calculate Q.  This requires the use of Excel's Goal Seek.  We simply find the
1. Guess a value of Re,
2. Calculate C and Q
3. Use C and Q to calculate Re
4. Use Goal Seek to change the value of Re we guessed in Step 1 until it's equal to the value calculated in Step 3
This process is automated in the Excel spreadsheet with a button linked to a VBA macro. The VBA macro simply initiates Goal Seek with the requireed settings.