Vortex flowmeter working principle and characteristics

The working principle of vortex flowmeter is to set a vortex generating body in the fluid, so that a regular vortex is alternately generated on both sides of the generating body. The vortex array is arranged asymmetrically downstream of the vortex generating body to generate a certain frequency, and the formula f= St*v/(1-1.27d/D)*d, (St is the Strouhal number, a dimensionless number, related to the vortex generator and Reynolds number; v is the flow velocity; d is the width of the oncoming face; D is the nominal diameter) to get the flow rate.

In general, the vortex flowmeter output signal (frequency) is not affected by changes in fluid properties and composition, which means that the meter factor is only related to the shape and size of the vortex generator and the Reynolds number. Its advantages are: simple and firm structure, convenient installation and maintenance; suitable for a variety of fluids, liquid, gas, steam and some mixed phases are applicable; high accuracy, generally about ± 1% R; wide range of flow, up to 10 : 1 or 20:1 or more; small head loss; no zero drift; relatively inexpensive price; disadvantage is: not suitable for low Re No. Re<20000, restrictions on the use of high viscosity, low flow rate, small diameter The requirements for the environment are relatively high, and places with vibrations should be eliminated as far as possible, and a long straight pipe section is required on the upstream side; the coefficient of the meter is lower, and the larger and lower the caliber, the lower. The signal resolution is reduced, so the caliber should not be too large, generally applied to DN15 ~ DN300mm.

1 advantages

The vortex flowmeter has a simple structure and is easy to install and maintain (compared with the throttling differential pressure flowmeter, it does not require a pressure-control pipe and a three-valve manifold, etc. to reduce leakage, blockage and freezing, etc.).

There are many types of fluids available, such as liquids, gases, vapors, and partially miscible fluids.

Accuracy is taught high (compared with differential pressure type, float type flowmeter), generally (±1% to ±2%) of the measured value has a small pressure loss (about 1/4 to 1/2 of the orifice flowmeter). Output pulse signal proportional to flow, suitable for total measurement, no zero drift; within a certain range of Reynolds number, the output frequency signal is not affected by fluid properties (density, viscosity) and components, that is, the meter coefficient only with the vortex Occurrence of the body and the shape of the pipe, only in a typical media check and apply to a variety of media.

2. Limitations

Vortex flowmeter is not suitable for low Reynolds number measurement (ReD ≥ 2×104), so it is limited in applications with high viscosity, low flow rate, and small diameter.

The stability of the vortex separation is affected by the distortion of the flow velocity distribution and the influence of the swirling flow, and a sufficiently long straight pipe section or a flow regulator (rectifier) ​​should be configured according to the different types of flow blockers on the upstream side. Generally, the differential pressure flow can be used as a reference. The straight length of the gauge requires installation. Compared with the turbine flow meter, the meter coefficient is low, the resolution is low, and the larger and lower the bore diameter, the general full-flow meter is used for DN300 or less. The instrument still lacks theoretical research and practical experience in pulsation flow and miscible flow.