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Key outcomes

  • Calibrated flow meter for non-ideal location
  • Operating uncertainty reduced

Venturi flow meters are a common method of measuring gas flow rates through ducting systems with minimal pressure drop or disruption to the flow. ISO 5167-1:2003(E) specifies the requirements of installation and operation of venturi flow meters. When built and installed in accordance with this standard, venturis do not need calibration as documented calibration values in the standard have been shown to provide flow measurements with accuracies of within 3 per cent. However, there are few industrial applications in process industries where the standard is perfectly applied. In such cases, it is necessary to calibrate the venturi meter under operating conditions.

A cut plane through a CFD model of a complex pipe junction, with 3 pipes joining. The complex flow prevents the use of standard calibration factors for a venturi flow meter.
Figure 1: Velocity contours in flow junctions near a venturi flow meter.

The client asked Synergetics to construct a Computational Fluid Dynamics (CFD) model of one such industrial application involving the merging of multiple flow streams with a series of 90° bends just upstream of the venturi as shown in Figure 1. The CFD model demonstrated how the flow through the venturi meter differed significantly from the ideal turbulent duct flow profile. Synergetics created a series of velocity profiles for analysis and developed a correction factor to calibrate the “as installed” venturi.

For further CFD examples of industrial process modelling see our sector page.