Industry new

Introduction to the bottleneck in the development of vortex flowmeters

Any flow meter can't be perfect, and the vortex flowmeter is no exception. After fully introducing its advantages, we will talk about its shortcomings and limitations, so that we can use our flowmeters to avoid weaknesses and reduce blindness.

The vortex flowmeter is a typical speed flowmeter. The stability of the vortex separation is affected by the flow field distortion and vortex flow upstream of the generator. Therefore, the installation instrument should be equipped with different lengths according to different forms of the upstream flow block. The downstream straight pipe section or the flow regulator is installed to provide good flow field conditions for the vortex flowmeter and eliminate the adverse effects of the flow field on the instrument. Compared with other speed flowmeters (turbo, electromagnetic, ultrasonic flowmeters), vortex flowmeters do not require upstream straight pipe lengths than they
Low; compared to the spiral vortex flowmeter and the jet flowmeter of the same fluid vibrating flowmeter, it requires higher length of the upstream straight pipe section.

The lower flow rate of the vortex flowmeter is subject to two conditions:
(1) Reynolds number impact. The lower limit Reynolds number of most vortex flowmeters is (l~2)xlW. Only when the instrument works in the area above the lower limit Reynolds number, the Strouhal number or the meter factor enters the straight section, and the instrument also enters. Human linear working area, otherwise nonlinear errors will occur. For vortex flowmeters operating at high viscosity and small bore conditions, the lower flow rate should not be too low.
(2) Limitation of the sensitivity of the detection component. The stronger the vortex intensity, the better the signal detection. The vortex intensity is proportional to the square of the flow velocity, so in the low velocity region of the lower limit of the range, the vortex signal is very weak, and whether the vortex signal can be effectively detected depends on the sensitivity of the detecting element.
Due to the above two factors, the lower limit flow rate of the vortex flowmeter should not be too low. In general, when measuring the liquid flow rate, the lower limit flow rate is 0.3 ~ 0.5mA; when measuring the gas, the lower limit flow rate is 3 ~ 5m / s.

The impact of pipeline vibration on the operation of vortex flowmeters is manifested in two aspects:
(1) Vibration has a certain influence on the stable separation of the vortex. The vortex flowmeter is a fluid vibrating flowmeter. When the working pipeline vibrates strongly and the vibration direction is perpendicular to the generating body, and the vibration frequency is the same as or similar to the vortex frequency, the vortex stable separation will be affected.
(2) Effect of vibration on force-sensitive detection components
The vortex flowmeter using the force sensitive detection element, the sensitivity of the force sensitive detection component should not be too low. Because the sensitivity is low, the sensitivity at the lower flow rate cannot be guaranteed. If the force generated by the vibration of the pipe reaches or exceeds the force generated by the vortex separation, the vibration force may cause interference to the normal operation of the detecting element.
The degree of influence of vibration is different for different types of detection techniques. Vortex flowmeters (such as thermal and ultrasonic vortex flowmeters) that detect local variations in flow rate are less affected by vibration. Vortex flow using force sensitive detection
The impact of vibration is greater. Among them, the stress vortex flowmeter is the most sensitive to vibration. In recent years, various manufacturers have taken many effective measures against the anti-vibration performance of vortex flowmeters and achieved certain results.

Compared with other pulse output type flow meters, the meter coefficient K of the vortex flowmeter is low, and as the meter diameter D increases, the meter factor K decreases approximately at the third power rate of the diameter ratio. As can be seen from Table 3-1.

Since the meter factor K decreases sharply as the diameter D of the measuring tube increases. Therefore, as the pipe diameter increases, the frequency of the instrument output signal also drops significantly for the same flow rate. Therefore, the diameter of the full-tube vortex flowmeter should not be too large, generally
300mm or less.

(1) Measure the liquid flow rate. At the upper limit of the range, care should be taken to avoid cavitation. In particular, when measuring static and high saturated vapor pressure liquids, special attention should be paid to the prevention of cavitation.
(2) The gas flow rate is measured, and the upper limit is affected by the gas compressibility. Generally, when measuring gas, the flow rate should be less than 0.2 Mach.

The effects of mixed-phase flow and pulsating flow on vortex flowmeters still lack theoretical and practical experience. Although some experiments on measuring mixed-phase flow are still in the exploration stage, they have not yet been put into practical use.
7. ^The history is short, "The basics and the actual path test
The history of vortex flowmeters is relatively short, and there is still a lot of work to be done in order to continue to explore and continuously enrich.
In summary, for a vortex flowmeter, a strong and stable Karman vortex street is the basis. Using a variety of inspection techniques in a variety of complex working conditions (high temperature,
Corrosion, vibration, etc., the effective detection of weak signals is a prerequisite for expanding the scope of application of the instrument. The signal processing circuit extracts the vortex signal from various noises and disturbances, which is an important part of improving the performance of the instrument.

PREVIOUS：Vortex electromagnetic flowmeter excellent deNEXT：Ultrasonic characteristics description Ultras