Orifice Plate Flow Calculator (ISO 5167-2)
Calculate liquid flow through a concentric orifice plate from the measured DP. The workbook iterates the Reader Harris/Gallagher discharge coefficient and Reynolds number, and checks the ISO 5167-2 limits.
Download
- Calculator sheet with a worked example
- How to Use sheet with steps
- 44 built in formulas, no macros
- Yellow input cells, grey results
- Calculation sign off block
- Excel, Google Sheets and LibreOffice
Worked Example
These are the results of the example already filled in the workbook. Replace the yellow cells with your own data.
Iteration of discharge coefficient C and Reynolds number
| Iteration | Re (assumed) | Discharge coefficient C | Mass flow (kg/s) | Re (calculated) |
|---|---|---|---|---|
| 1 | 1,000,000 | 0.60626 | 14.4311 | 179,323 |
| 2 | 179,323 | 0.60959 | 14.5105 | 180,309 |
| 3 | 180,309 | 0.60958 | 14.5101 | 180,305 |
| 4 | 180,305 | 0.60958 | 14.5101 | 180,305 |
| 5 | 180,305 | 0.60958 | 14.5101 | 180,305 |
| 6 | 180,305 | 0.60958 | 14.5101 | 180,305 |
| 7 | 180,305 | 0.60958 | 14.5101 | 180,305 |
| 8 | 180,305 | 0.60958 | 14.5101 | 180,305 |
About this Calculator
The orifice plate is still the most widely used flowmeter in process plants. Its discharge coefficient depends on Reynolds number, which depends on the flow you are trying to find, so the calculation must be iterated. This workbook does the iteration visibly, row by row, so the result can be checked and audited.
Basis: ISO 5167-2:2003 Reader Harris/Gallagher equation for C and permanent pressure loss; liquid service (ε = 1).
How to use
- Enter the measured pipe inside diameter and the orifice bore at operating temperature.
- Enter the DP in mbar and the liquid density and viscosity at flowing conditions.
- Choose the tapping arrangement; L1 and L2' follow automatically.
- The iteration table refines C and Re; the last row gives the result.
- Check that the ISO 5167-2 limits row shows OK.
Formulas used
- β = d ÷ D, E = 1 ÷ √(1 − β⁴).
- C from the Reader Harris/Gallagher equation (ISO 5167-2).
- qm = C × E × (π ÷ 4) × d² × √(2 × ΔP × ρ).
- Re = 4 qm ÷ (π μ D), fed back into C until it converges.
Related tools
Frequently Asked Questions
What is the Reader Harris/Gallagher equation?
The empirical equation in ISO 5167-2 that gives the discharge coefficient C of an orifice plate as a function of β, Reynolds number and tapping position.
Why does the orifice calculation need iteration?
C depends on Reynolds number, and Reynolds number depends on the flow being calculated. A few passes converge on the answer.
What are flange taps?
Pressure tappings 25.4 mm (1 inch) upstream and downstream of the plate faces, the most common arrangement.
Learn more on the blog
5 costly DP flow measurement errors
A practical guide on instrumentationblog.in that explains the engineering behind this workbook.
Read Full Article