Working principle of vortex flowmeter

Project Overview

Vortex flowmeter is a very common and widely used instrument. Especially in recent years, the times have developed rapidly, and the development of modern industrial enterprises has been particularly significant. To some extent, it is inseparable from the participation of flow meters. In particular, vortex flow meters have a very high click rate, such as petroleum, metallurgy, food, pharmaceuticals, chemicals, power plants, and urban buildings. Vortex flowmeters are found in various industries.

It is characterized by small pressure loss, large measuring range, and high accuracy. When measuring the volume flow rate under working conditions, it is almost not affected by parameters such as fluid density, pressure, temperature, and viscosity. There are no moving mechanical parts, so reliability is high and maintenance is low. Instrument parameters can be stable for a long time.

What is the working principle of vortex flowmeter?

The vortex flowmeter is a fluid oscillating flow meter with excellent technical performance indicators developed based on the "Karman vortex" principle. A non-streamlined columnar flow meter is inserted into the sensor housing through which the fluid flows. When an object is hit, two rows of staggered vortices will be generated on both sides behind the cylinder, as shown in Figure (1).

Figure (1): Karman vortex street diagram (2) Relationship between St and Re

The frequency of vortex separation is proportional to the flow rate and inversely proportional to the width of the cylinder. It can be used The following formula is expressed:

Where: f: vortex separation frequency;

St: dimensionless constant (Strauhal number);

V: The average flow velocity of the fluid in the pipe;

d: The width of the upstream surface of the cylinder;

D: The inner diameter of the sensor housing.

The fluid flow velocity and instantaneous flow rate can be measured by detecting the separation frequency. The Strouhal number St, for a specific columnar vortex generator, is a function of the Reynolds number Re within a certain flow range, St. The linear part of the function with Re is the linear measurement range of the vortex flow sensor, as shown in Figure (2). Therefore, the average flow rate and volume flow rate of the fluid in the pipeline can be determined by detecting the separation frequency f.

The number of pulses generated by a unit volume of fluid flowing through the sensor is called the instrument coefficient, represented by K

(Formula 2):

k＝N／ Q (1/m3)………………………………(2)

In the formula: k: instrument coefficient;

N: number of pulses;

Q: Fluid volume.

The vortices separate alternately on both sides of the rear column, generating pressure pulsations, which subject the detection body (also called the probe) in the sensor to an alternating force. See Figure (3). The piezoelectric sensor embedded in the detection body The crystal element is subjected to the action of alternating force to generate a charge frequency signal. After being processed by the detection circuit, it is output in the form of a frequency signal or converted into a standard signal form. When equipped with flow totalizing instruments and temperature and pressure sensors, parameters can be corrected and calculated.

The vortex flowmeter uses a piezoelectric stress sensor, which is highly reliable and can work in the operating temperature range of -20°C to +250°C. There are analog standard signals and digital pulse signals.Output, easy to use with digital systems such as computers, it is a relatively advanced and ideal measuring instrument.