Vortex flowmeter belongs to a type of velocity flowmeter, mainly used for flow measurement of industrial pipeline medium fluids, such as gas, liquid, steam and other media.

Its characteristics are small pressure loss, large range, moderate accuracy, and almost unaffected by parameters such as fluid density, pressure, temperature, viscosity, etc. when measuring fluid volume flow rate.

Due to the absence of movable mechanical parts, vortex flowmeters have a simple structure, high reliability, low maintenance, and large flow capacity (compared to other flow meters of the same caliber, they can pass through a larger flow rate). Due to these characteristics, vortex flowmeters have become one of the commonly used flow meters.

1、 Working principle of vortex flowmeter: The vortex flowmeter applies the principle of fluid oscillation to measure flow rate. A triangular cylindrical vortex generator (with various shapes) is set in the fluid, and regular vortices are alternately generated from both sides of the vortex generator. These vortices are called Karman vortices, which are asymmetrically arranged downstream of the vortex generator

The release frequency of vortices is related to the average velocity of the fluid flowing through the vortex generator and the characteristic width of the vortex generator, which can be expressed by formula 1: f is the output frequency, in Hz; v is the average velocity of the fluid flowing through the vortex generator, in m/s; D is the width of the upstream face of the vortex generator, measured in meters; D is the inner diameter of the pipeline, measured in meters; St is the Strouhal number, a dimensionless number that is related to the shape of the vortex and the Reynolds number. From Figure 2, it can be seen that the Strouhal number is considered a constant within a certain range of Reynolds numbers.

It can be seen from this that when the Strouhal number is considered constant, the frequency of the vortex generator is only related to the flow velocity after the width of the upstream face and the diameter of the process pipe are determined.

The flow equation of vortex flowmeter: where qv is the volumetric flow rate, m3/s； QM is the mass flow rate, kg/s； F is the frequency of the sensor output signal, Hz; K is the instrument coefficient of the sensor; ρ is the fluid density, kg/ m3。 When measuring gas, the flow equation of the vortex flowmeter is: where Pn and Tn are the pressure and temperature under standard conditions, respectively; Z. Zn represents the gas compressibility coefficients under working and standard conditions, respectively; Qvn is the volumetric flow rate under standard conditions (20 ℃, 101.32kPa), m3/s； P. The instrument coefficient k values of the pressure and temperature sensors under working conditions are calibrated by a flow standard device, and the calibration medium is usually water or air.

From this, it can be seen that the frequency output signal of a general vortex flowmeter is not affected by changes in fluid properties and components, and is only related to the instrument coefficient K, the shape and size of the vortex generator, and the Reynolds number. However, when the instrument coefficient K and the shape and size of the vortex generator are determined before the product leaves the factory, and the Reynolds number is within the accuracy guarantee range, the frequency output signal of the vortex flowmeter is only related to the flow rate.

However, when we need mass flow rate, we also need to obtain the density of the fluid while obtaining the volumetric flow rate. This requires detecting parameters that affect the density, such as temperature, pressure, etc., and correcting the density.

2、 There are many types of classification for vortex flowmeters, and the one we commonly use is to classify them according to the sensor connection method,

Divided into: 1) flange connection type; 2) Clamp type (also known as clamping type); According to the composition of sensors and converters, they are classified into: 1) integrated type; 2) Separated type; According to the structural form of sensors, they are classified into: 1) full tube type; 2) Insertion type.

3、 The structural vortex flowmeter generally consists of four parts: vortex generator, vortex detector, instrument body, and converter. 1. Vortex generator. Vortex generators are divided into single vortex generators and multi vortex generators. The commonly used type is a single vortex generator, which has basic shapes such as triangle, circle, rectangle, etc. Combining single vortex generators results in a multi vortex generator, which has a certain effect on improving vortex street strength, stability, and reducing the lower limit of Reynolds number.

2. Vortex detector. There are generally five ways to detect vortices: 1) Installing detection elements inside the vortex generator to directly detect the differential pressure on both sides of the generator; 2) Open pressure holes on the vortex generator and install detection elements in the pressure holes to detect the differential pressure on both sides of the generator; 3) Detecting the alternating circulation around the vortex generator; 4) Detecting the alternating circulation on the back of the vortex generator; 5) Detecting vortex columns in the wake. By using the five detection methods mentioned above, a variety of vortex flowmeter sensors are formed by using detection elements with thermal sensitivity, stress, strain, capacitance, optoelectronics, ultrasound and other technologies.

3. Converter. The vortex signal detected by the sensor is processed through amplification, filtering, shaping, etc., and converted into a pulse signal or a two-wire 4-20mA current signal according to actual needs, for use by secondary instruments or control systems.

4. Instrument body. The structure and materials of the instrument body should be determined based on parameters such as temperature, pressure, and corrosiveness of the measured medium, which also have a significant impact on measurement accuracy.

4、 The main features of vortex flowmeter are: 1) simple and sturdy structure, no movable parts, easy installation and maintenance; 2) There are many types of fluids that can be measured, including liquids, gases, vapors, etc., including some mixed phase flow media; 3) The detection sensor does not directly contact the measured medium, with stable performance and long service life; 4) The output is a pulse signal proportional to the flow rate, with no zero drift and high accuracy; 5) Wide measurement range, with a range ratio of up to 10:1, and special needs up to 20:1 or higher; 6) Less pressure loss (compared to orifice flow meters), lower operating costs, and more energy-saving significance.

7) Within a certain Reynolds number range, it is not affected by fluid properties and components, but only by instrument coefficients and the shape and size of vortex generators, making it easier to achieve standardized design for detection components;

8) High cost-effectiveness, vortex flowmeter is an economical and practical type among many flow meters.

9) High safety, if the detection component fails, it will not cause pipeline interruption;

5、 Attention: No matter how good an instrument is, if the design, selection, and installation are not correct, it will not have good results. When designing the project, we should pay attention to: 1. Consider the process parameters: 1) Make sure that the vortex generator generates a vortex and the detection element works within the guaranteed accuracy range. Not suitable for detecting low Reynolds number or high viscosity fluid media, as low Reynolds number fluids have poor linearity and high viscosity fluids are not suitable for forming vortices; 2) The presence of small particles or bubbles in the measured medium exceeding a certain proportion can affect the deviation of instrument coefficients, and should be used with caution when selecting; 3) For pulsating fluids, it is easy to superimpose the frequency of fluid pulsation onto the working pulse of the vortex generator, causing resonance, which should be avoided when selecting; 4) For fluids containing solid particles, the erosion of the vortex generator will wear down the vortex generator. If the fluid containing fiber dirt wraps around the vortex generator, it will affect its service life and measurement accuracy; 5) Consider the corrosiveness of the medium; 6) Insertion type is suitable for measuring the flow rate of large-diameter pipelines.

2. Installation environment: 1) Sensors should be avoided from being installed on pipelines with strong mechanical vibrations (such as pump outlets). If it is unavoidable, seismic measures should be taken; 2) Sensors (including shielded cables connecting them) should be avoided from being installed in environments with high temperature heat sources, radiation sources, strong electromagnetic field interference, and strong corrosion; 3) Consider the space for easy installation and maintenance of instruments; 4) Consider safety and protection levels. 3. Installation method: 1) Ensure the straight pipe sections before and after the flowmeter (refer to the straight pipe section requirements in the instrument product manual, the more it meets the requirements, the higher the measurement accuracy); 2) Vortex flowmeters are commonly installed horizontally. When measuring liquid flow, if the measured liquid contains a small amount of gas, the sensor should be installed at a lower part of the pipeline. When measuring gas flow, if the measured gas contains a small amount of liquid, the sensor should be installed at a higher part of the pipeline; When installed vertically, the flow of liquid is from bottom to top, and the flow of gas is not limited. However, if the gas contains a small amount of liquid, the flow of gas must be from bottom to top. 3) When measuring superheated steam, saturated steam, and low-temperature liquids on a horizontal pipeline, if conditions permit, side installation can be used to minimize the impact of fluid temperature on the amplifier (any sensor installed on a horizontal pipeline can be installed on the upper side of the pipeline).