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Vortex Shedding Flowmeter
Jan 25, 2019


Vortex flowmeters|Vortex shedding flow meter




Vortex flowmeters are also known as vortex flowmeters\Vortex shedding flow meter or Karman vortex flowmeters.

Comprehensively absorbing the advanced technology of developed countries and summarizing the research and production experience for many years, the products have been carefully designed to realize the product intelligence, standardization, serialization, generalization, production and mold, and ensure the beauty of product quality. The product has the characteristics of advanced circuit, low power consumption, wide range ratio, simple structure, small resistance loss, sturdy and durable, wide application, long service life, stable operation and easy installation and debugging.


The vortex shedding flowmeter is a volumetric flowmeter that measures the volumetric flow rate of a gas, vapor or liquid, the volumetric flow rate of a standard condition, or the mass flow rate according to the principle of Karman vortex. It is mainly used for flow measurement of industrial pipeline medium fluids, such as gas, liquid, steam and other media.

The vortex flowmeter is characterized by small pressure loss, large measuring range and high precision. It is almost unaffected by parameters such as fluid density, pressure, temperature and viscosity when measuring the volume flow rate. No moving mechanical parts, so high reliability and low maintenance. Instrument parameters can be stable for a long time. The vortex shedding flowmeter uses a piezoelectric stress sensor with high reliability and can operate in the operating temperature range of -20 °C to +250 °C. There are analog standard signals and digital pulse signal outputs, which are easy to use with digital systems such as computers. It is a relatively advanced and ideal measuring instrument.

Vortex flowmeters|Vortex shedding flow meter

Working principle of vortex flowmeter:

When a triangular column type vortex generator is provided in the fluid, regular vortices are alternately generated from both sides of the vortex generator. These vortices are called Karman vortices, and the vortex rows are arranged asymmetrically downstream of the vortex generator.

The vortex flowmeter is a volumetric flowmeter that measures the volumetric flow of a gas, vapor or liquid, the volumetric flow rate of a standard condition, or the mass flow rate according to the Karman vortex street principle (Kármán Vortex Street). It can also be used as a flow transmitter in an automated control system.

The vortex flowmeter uses the principle of fluid oscillation to measure the flow. When the fluid passes through the vortex flow transmitter in the pipeline, it alternately produces two rows of vortices proportional to the flow velocity after the vortex generator of the triangular prism. The release frequency of the vortex and The average velocity of the fluid flowing through the vortex generator is related to the characteristic width of the vortex generator, which can be expressed by the following formula:

 

Where: is the release frequency of the vortex, the unit is Hz; v is the average velocity of the fluid flowing through the vortex generator, the unit is m/s; d is the characteristic width of the vortex generator, the unit is m; St is Strauhar The Strouhal number, dimensionless, has a value range of 0.14-0.27.

St is a function of the Reynolds number.

When the Reynolds number Re is in the range, the St value is about 0.2. In the measurement, try to meet the Reynolds number of the fluid at this time, the vortex frequency.

Thus, by measuring the vortex frequency, the average velocity v of the fluid flowing through the vortex generator can be calculated, and the flow rate q can be obtained by the equation, where A is the cross-sectional area of the fluid flowing through the vortex generator.


Technical indicators of vortex flowmeter:

Measuring medium: gas, liquid, steam

Connection method: flanged, flanged, plug-in

Caliber specifications Flange card mounting caliber 25,32,50,80,100

Flange connection type selection 100,150,200

Flow measurement range Normal measurement flow rate range Reynolds number 1.5 × 104 ~ 4 × 106; gas 5 ~ 50m / s; liquid 0.5 ~ 7m / s.

Normal measurement flow range The measurement range of liquid and gas flow is shown in Table 2; the steam flow range is shown in Table 3.

Measurement accuracy 1.0 level 1.5 level

Temperature of the measured medium: normal temperature –25°C~100°C, high temperature –25°C~150°C -25°C~250°C

Output signal Pulse voltage output signal High level 8~10V Low level 0.7~1.3V

Pulse duty cycle is about 50%, transmission distance is 100m

Pulse current remote transmission signal 4~20 mA, transmission distance is 1000m

Instrument use environment Temperature: -25 ° C ~ +55 ° C Humidity: 5 ~ 90% RH50 ° C

Material Stainless steel, aluminum alloy

Power supply DC24V or lithium battery 3.6V

Explosion-proof grade Intrinsic safety type iaIIbT3-T6, protection class IP65.

vortex flowmeter

Product Features of vortex flowmeter:

The body is also integrated with the temperature compensation compensation function to measure the standard volume flow or standard mass flow of the fluid.

Fully intelligent, digital circuit design, can automatically compensate for the measured fluid density or standard volume calculation.

New digital filtering and correction features make flow measurement more accurate and reliable.

The battery-powered version can operate continuously for more than two years without an external power supply.

The new dot matrix Chinese character LCD display makes it easier to use.

Features:

The structure is simple and firm, has no moving parts, high reliability and long-term operation is very reliable.

Easy to install and easy to maintain.

The detection sensor does not directly contact the measured medium, and the performance is stable and the life is long.

The output is a pulse signal proportional to the flow rate, with no zero drift and high precision.

The measuring range is wide and the turndown ratio is up to 1:10.

The pressure loss is small, the operating cost is low, and it is more energy-saving.

In a certain Reynolds number range, the output signal frequency is not affected by fluid physical properties and composition changes. The meter factor is only related to the shape and size of the vortex generator. There is no need to compensate when measuring the volume flow of the fluid. Calibrate the meter factor.

Wide range of applications, steam, gas, liquid flow can be measured.

The verification period is two years.

Vortex flow sensor application inner diameter range of 25-300mm (full tube type)

The plug-in vortex flow sensor has an internal diameter range of 350-1200 mm (plug-in type).

Full tube measurement liquid accuracy is 1%

Measuring steam and gas accuracy is 1.5% [3]

Plug-in measurement liquid accuracy is 2%

Measuring steam and gas accuracy is 2.5%

The measured medium temperature is -20~150°C, -40~250°C, +100~350°C (only tube type)

The output signal is a three-wire voltage pulse, a three-wire system of 4-20 mA, and a two-wire system of 4-20 mA.

Installation conditions of vortex flowmeter:

The sensor should be mounted on a pipe of the same diameter as horizontal, vertical, and inclined (liquid flow from bottom to top). The upstream and lower 2 swims of the sensor shall be equipped with a straight pipe section of a certain length, and the length shall be in accordance with the requirements of the front straight pipe section 15-20D and the rear straight pipe section 5~1OD. [4]

The nearby pipe in which the liquid sensor is installed should be filled with the liquid to be tested.

The sensor should be protected from installation on pipes with strong mechanical vibrations.

The inner diameter of the straight pipe section should be as close as possible to the sensor diameter. If it is not consistent, the pipe with a slightly larger diameter than the sensor should be used. The error should be ≤3% and not more than 5mm.

The sensor should be protected from installations with strong electromagnetic interference, small space and inconvenient maintenance.

vortex flowmeter

Installation requirements of vortex flowmeter:

1. Reasonably choose the installation site and environment.

Avoid strong power equipment, high-frequency equipment, strong power switch equipment; avoid the influence of high-temperature heat source and radiation source, avoid strong vibration places and strong corrosive environment, and consider installation and maintenance.

2. There must be enough straight pipe sections in the upstream and downstream.

If there are two 90° elbows on the same plane upstream of the sensor installation point, then: the upstream straight pipe section is ≥25D, and the downstream straight pipe section is ≥5D.

If there are two 90° elbows on different planes upstream of the sensor installation point, then: the upstream straight pipe section is ≥40D, and the downstream straight pipe section is ≥5D.

The regulating valve should be installed outside the 5D downstream of the sensor. If it must be installed upstream of the sensor, the straight pipe section upstream of the sensor should be no less than 50D, and the downstream should be no less than 5D.

3. The piping on the upstream and downstream of the installation point should be concentric with the sensor, and the coaxial deviation should be no less than 0.5DN.

4. The pipeline adopts measures to reduce vibration.

The sensor should be avoided as far as possible on the pipe with strong vibration, especially lateral vibration. If it is necessary to install, vibration damping measures must be taken. Pipe fastening devices are installed at the upstream and downstream 2D of the sensor, and anti-vibration pads are added.

5. Installation on horizontal pipes is the most common installation method for flow sensors.

When measuring the gas flow rate, if the measured gas contains a small amount of liquid, the sensor should be installed at a higher position in the pipeline.

When measuring the liquid flow rate, if the measured liquid contains a small amount of gas, the sensor should be installed in the lower part of the pipeline.

6. The sensor is installed in a vertical pipe.

When measuring gas flow, the sensor can be mounted on a vertical pipe with unlimited flow. If the gas to be measured contains a small amount of liquid, the gas flow should be from bottom to top.

When measuring the flow of liquid, the flow of liquid should be from bottom to top: this does not add extra weight to the probe.

7. The sensor is mounted on the side of the horizontal pipe.

Regardless of the fluid being measured, the sensor can be mounted sideways on a horizontal pipe, especially for superheated steam, saturated steam and cryogenic liquids. If conditions permit, side-loading is preferred, so that the temperature of the fluid has less effect on the amplifier.

8. The sensor is flipped in the horizontal pipe.

This installation method is generally not recommended. This method of installation is not suitable for measuring general gases and superheated steam. It can be used to measure saturated steam and is suitable for measuring high temperature liquids or when cleaning pipes frequently.

9. The sensor is installed on the pipeline with insulation.

When measuring high temperature steam, the insulation layer should not exceed one third of the height of the bracket.

10. Selection of pressure measurement points and temperature measurement points.

According to the needs of the measurement, when measuring the pressure and temperature near the sensor, the pressure measurement point should be 3-5D downstream of the sensor, and the temperature measurement point should be 6-8D downstream of the sensor.


Vortex flowmeter Selection

The correct selection of the vortex flowmeter can ensure better use of the vortex shedding flowmeter. What kind of vortex flowmeter should be selected according to the physical and chemical properties of the fluid medium to be tested? The vortex flowmeter's diameter, flow range, lining material, electrode material and output current can be adapted to the fluid to be measured. The nature and requirements of flow measurement.

1, precision function check

Accuracy class and function According to the measurement requirements and use occasions, the instrument accuracy level is selected to achieve economical efficiency. For example, in the case of trade settlement, product handover and energy measurement, the accuracy level should be higher, such as 1.0, 0.5, or higher; for process control, select different accuracy levels according to control requirements; It is to detect the process flow, no need to do precise control and measurement, you can choose a lower accuracy level, such as 1.5, 2.5, or even 4.0, then you can use the low-cost plug-in vortex flowmeter.

2, measurable medium

Measuring medium flow rate, meter range and caliber When measuring a general medium, the full flow of the vortex flowmeter can be selected within the range of 0.5-12 m/s of the measured medium flow rate, and the range is relatively wide. The meter specification (caliber) is not necessarily the same as the process pipeline. It should be determined whether the measured flow range is within the flow rate range. That is, when the pipeline flow rate is too low to meet the flow meter requirements or the measurement accuracy cannot be guaranteed at this flow rate, It is necessary to reduce the gauge diameter, thereby increasing the flow rate inside the tube and obtaining satisfactory measurement results.

3, the choice of vortex flow transmitter

In the measurement of saturated steam, VA type piezoelectric vortex flow transmitter is adopted. Because of the wide range of vortex flowmeter, in practical applications, it is generally considered that the flow of measuring saturated steam should not be lower than that of vortex flowmeter. The lower limit, that is to say, the fluid flow rate must not be less than 5 m/s. According to the size of the steam, the vortex flow transmitters with different calibers are selected, and the caliber of the transmitter cannot be selected by the existing process pipe diameter.

4, the choice of pressure compensation pressure transmitter

Since the saturated steam line is long and the pressure fluctuates greatly, pressure compensation must be used. Considering the correspondence between pressure, temperature and density, only pressure compensation can be used in the measurement. Since the pipeline saturated steam pressure is in the range of 0.3-0.7 MPa, the pressure The range of the transmitter can be selected as 1 MPa.

5, display instrument selection

Display instrument intelligent flow display instrument with voltage regulation compensation, instantaneous flow display and cumulative flow accumulation function.

vortex  steam flowmeter

Measuring steam with vortex flowmeter:

Vortex flowmeter is mainly used for flow measurement of industrial pipeline medium fluid, such as gas, liquid, steam and other media. It is a relatively advanced and ideal flow meter.

There are three ways to measure steam in a vortex flowmeter:

The first and most widely used vortex flowmeter with temperature and pressure compensation. This is an indirect vortex mass flowmeter. In actual use, the density is measured indirectly by temperature and pressure measurement, and multiplied by the volume measured by the vortex flowmeter to calculate the mass. This is the most common form of measurement of steam by the Suco Instrument Vortex Flowmeter.

Second, the lift vortex flowmeter directly measures the mass of the medium. The theoretical basis is that the mass flow rate of the medium has a certain proportional relationship with the intensity of the vortex. Calculating the vortex intensity can directly calculate the mass of the medium. This flowmeter has been produced in Yokogawa, Japan, but the accuracy is not ideal and the market utilization rate is not high. ·

The last one is the differential pressure vortex mass flowmeter, differential pressure signal + vortex flowmeter = differential pressure vortex mass flowmeter. The differential pressure signal is the pressure difference between the two pressure tapping holes at a specific position on the body and downstream. The axes of the two pressure tapping holes should be in the same plane as the axis of the generating body. The distance of the pressure tapping hole has a significant influence on the magnitude and stability of the differential pressure value. The distance is close, the differential pressure signal is large, but the stability is poor; the distance is far, the opposite is true. Through testing, it is important to choose the appropriate pressure tapping location. Compared to the lift vortex mass flow meter, this meter is simpler and easier to implement. Domestic manufacturers have invested in development and obtained invention patents, and the products have been applied in some enterprises.



There are several areas in the application of vortex flowmeter flow measurement technology and instrumentation.

Industrial production process

Flow meter is one of the large-scale instruments in process automation instruments and devices. It is widely used in metallurgy, electric power, coal, chemical, petroleum, transportation, construction, textile, food, medicine [7], agriculture, environmental protection and People's daily life and other areas of the national economy are important tools for developing industrial and agricultural production, saving energy, improving product quality, and improving economic efficiency and management level. They play an important role in the national economy. In process automation instruments and devices, flow meters have two functions: as a test instrument for the process automation control system and a total meter for measuring the quantity of materials.

Energy metering

Energy is divided into primary energy (coal, crude oil, coalbed methane, petroleum gas and natural gas), secondary energy (electric power, coke, artificial gas, refined oil, liquefied petroleum gas, steam) and energy-carrying medium (compressed air, oxygen, Nitrogen, hydrogen, water, etc. Energy metering is an important means of scientifically managing energy, achieving energy conservation and reducing consumption, and improving economic efficiency. Flow meters are an important part of energy metering. The commonly used energy sources of water, artificial gas, natural gas, steam and oil use extremely large flow meters, which are indispensable tools for energy management and economic accounting.

Environmental protection engineering

The emissions of flue gas, waste liquid, sewage, etc. seriously pollute the atmosphere and water resources, and seriously threaten the human living environment. The state regards sustainable development as a national policy, and environmental protection will be the biggest issue in the 21st century. Air and water pollution must be controlled, management must be strengthened, and management is based on quantitative control of pollution.

China is a country with coal as its main energy source. There are millions of chimneys in the country that continuously emit smoke into the atmosphere. Flue gas emission control is an important project to cure pollution. Each chimney must be equipped with a flue gas analysis instrument and a flow meter to form a flail emission monitoring system. The flow rate of flue gas is very difficult. The difficulty is that the chimney is large in size and irregular in shape, the gas composition changes indefinitely, the flow rate range is large, dirt, dust, corrosion, high temperature, and no straight pipe section.

Transportation

There are five ways: railway, air, water, and pipeline transportation. Although pipeline transportation has already existed, the application is not common. With the outstanding environmental protection issues, the characteristics of pipeline transportation have attracted people's attention. Pipeline transportation must be equipped with a flow meter, which is the eye for control, distribution and dispatch. It is also an indispensable tool for safety monitoring and economic accounting.

The flowmeter has certain requirements on the upstream and downstream straight pipe sections at the installation point, otherwise it will affect the measurement accuracy.

vortex flowmeter

Advantages and disadvantages of vortex flowmeters:

The advantages of the vortex flowmeter are:


1) The vortex flowmeter has no moving parts, and the measuring component has a simple structure, reliable performance and long service life.


2) The vortex flowmeter has a wide measuring range. The turndown ratio can generally reach 1:10.


3) The volume flow of the vortex flowmeter is not affected by thermal parameters such as temperature, pressure, density or viscosity of the fluid being measured. Generally no separate calibration is required. It measures the flow of liquids, gases or vapors.


4) It causes little pressure loss.


5) High accuracy, repeatability of 0.5%, and low maintenance.


The disadvantages of street flow meters are:


1) The volume flow rate under the working condition of the vortex flowmeter is not affected by the thermal parameters such as temperature, pressure and density of the measured fluid, but the final measurement result of the liquid or steam should be the mass flow. For the gas, the final measurement result should be Standard volume flow. Mass flow or standard volume flow must be converted by fluid density and fluid density changes due to changes in fluid conditions must be considered.


2) The main factors causing the flow measurement error are: the measurement error caused by the uneven flow velocity; the medium density when the fluid condition changes can not be accurately determined; the wet saturated steam is assumed to be dry saturated steam for measurement. If these errors are not limited or eliminated, the total measurement error of the vortex flowmeter will be large.


3) Poor anti-vibration performance. External vibrations can cause measurement errors in the vortex flowmeter and may not even work properly. The high flow velocity shock of the channel fluid causes additional vibration of the cantilever of the vortex generating body, which reduces the measurement accuracy. The impact of large diameters is more obvious.


4) Poor adaptability to the measurement of dirty media. The generator of the vortex flowmeter is easily smeared by the dirt or entangled by the dirt, which changes the size of the geometry and greatly affects the measurement accuracy.


5) The requirements for straight pipe sections are high. Experts pointed out that the straight pipe section of the vortex flowmeter must ensure 20D after the first 40D to meet the measurement requirements.


6) Poor temperature resistance. Vortex flowmeters generally only measure fluid flow in media below 300 °C.


You can choose all kinds of vortex flow meter,like:

Compressed Air Flow Meter

Nitrogen Flow Meter

Steam Flow Meter 

Temperature And Pressure Compensation Of  Vortex Flow Meter


We also share vortex konwledge,like:

THE Measurement Error Of Vortex Flowmeter

How To Install Vortex Flowmeter

Vortex Flowmeter Is A Common Choice For Natural Gas Flow

Vortex flowmeter measures compressed air




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