1. What is a vortex flow meter?
A vortex flow meter measures the flow rate by detecting the vortices shed from a bluff body placed in the flow stream. It uses the Von Kármán effect.
2. What is the principle behind vortex flow meters?
Vortex flow meters operate on the Von Kármán Vortex Street principle. When a fluid flows past a bluff body, vortices are alternately shed on both sides. The frequency of vortex shedding is proportional to the flow velocity.
3. What is a bluff body?
A bluff body is a non-streamlined object placed in the flow path to generate vortices. Its shape and dimension are critical for proper vortex formation and meter calibration.
4. What is the relationship between vortex frequency and flow rate?
f=St⋅Vdf = \frac{St \cdot V}{d}
Where:
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ff = vortex frequency
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StSt = Strouhal number (dimensionless)
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VV = flow velocity
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dd = width of the bluff body
5. What is the Strouhal number?
The Strouhal number (St) is a dimensionless number representing the ratio of vortex shedding frequency to the flow velocity and characteristic dimension. It remains constant over a specific Reynolds number range.
6. Can vortex flow meters measure gases and steam?
Yes. Vortex meters are suitable for liquids, gases, and steam, especially saturated or superheated steam, due to their high-temperature capability and pressure tolerance.
7. What are the advantages of vortex flow meters?
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No moving parts → low maintenance
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Wide rangeability
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Suitable for high temperatures and pressures
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Good accuracy for clean fluids
8. What are the limitations of vortex flow meters?
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Not suitable for slurry or viscous fluids
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Requires a minimum Reynolds number (typically >10,000)
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Low flow detection is limited
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Sensitive to vibration and pulsating flows
9. How is flow direction handled in vortex flow meters?
Most vortex meters are unidirectional. Installation should follow the flow direction marked on the meter body. Bidirectional models are also available.
10. How is the output of a vortex flow meter typically transmitted?
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Frequency output (proportional to vortex shedding rate)
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4-20 mA analog signal
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HART/Modbus/Fieldbus (for smart meters)
11. How much straight run piping is required before and after a vortex meter?
Typical recommendations:
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Upstream: 10–20 diameters
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Downstream: 5 diameters
Exact requirements depend on upstream disturbances like valves, elbows, etc.
12. Can vortex meters be used in custody transfer applications?
No, vortex meters are not typically used for custody transfer, as they don’t meet the strict accuracy and repeatability standards required.
13. How is temperature and pressure compensation applied in vortex flow measurement?
For mass flow or energy flow (especially for gases/steam), a multivariable vortex meter integrates pressure and temperature sensors to perform real-time compensation.
14. What is the typical accuracy of a vortex flow meter?
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Liquid: ±0.5 to ±1% of reading
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Gas/Steam: ±1 to ±2% of reading
Higher accuracy requires stable flow and proper installation.
15. What are common causes of error in vortex flow measurement?
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Pipe vibration
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Improper installation (upstream/downstream disturbance)
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Two-phase flow (air bubbles or entrained gas)
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Deposits on bluff body or sensor
16. What is the minimum Reynolds number required for vortex shedding?
Typically, a Reynolds number > 10,000 is required for stable vortex formation and accurate measurement.
17. What is the difference between inline and insertion vortex meters?
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Inline: Measures full pipe flow, higher accuracy
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Insertion: Installed through a tap, suitable for large pipe sizes, cost-effective for big pipelines
18. What maintenance is required for vortex meters?
Minimal. Periodic inspection for deposits, sensor integrity, and leak checks is generally sufficient. No moving parts reduce wear and tear.
19. How is a vortex meter calibrated?
Calibration is typically performed at the factory using flow rigs. Field calibration can be done by comparing against a reference standard or using simulation for electronic calibration.
20. How do vortex meters handle two-phase flow or entrained air?
Vortex meters are not ideal for two-phase flow. Entrained air or bubbles can cause erratic vortex formation, leading to inaccurate measurements.