Equipment Selection | How to Choose a Suitable Vortex Flowmeter
2023-8-11512
Vortex street flowmeter is a flowmeter produced based on the Carmen vortex street principle. Mainly used for flow measurement of industrial pipeline medium fluids, such as gases, liquids, steam, and other media. Its characteristics are small pressure loss, large range, high accuracy, and almost unaffected by parameters such as fluid density, pressure, temperature, and viscosity when measuring the volumetric flow rate under working conditions.
The vortex flowmeter has no movable mechanical parts, therefore it has high reliability, low maintenance, and long-term stable instrument performance. When choosing a vortex flowmeter, multiple factors need to be considered, including operating conditions, fluid properties, accuracy requirements, etc.
So how should the vortex flow meter be specifically selected? I hope the following selection methods can help everyone:
1. Tested medium
Vortex flowmeters are generally suitable for gases, liquids, steam and other media, but the following media are not suitable for using vortex flowmeters for measurement:
① Fluids containing a large amount of solid particles or suspended solids;
② Medium with excessive kinematic viscosity under operating conditions, such as some high viscosity oils (such as heavy oil).
In addition, for the name of the tested medium, if the medium is steam, it is necessary to indicate whether it is saturated steam or superheated steam.
2. Flow range
① The commonly used flow rate should be controlled in the upper and middle measurable range of the vortex street:
Due to the susceptibility of pipeline vibration to the measurement of vortex street lower limit flow, it is advisable to avoid measurements with lower limits as much as possible.
② When the flow range exceeds the measurable range of the vortex flowmeter, the method of reducing or expanding the diameter can be adopted, but attention should be paid to:
The reduction and expansion of the instrument should not be too large. After the reduction, the flow rate increases, which increases resistance and back pressure. However, the expansion is prone to cavitation;
If the straight pipe section allows, the "variable diameter head+straight pipe section" should be selected to ensure stable measurement of the fluid;
The selection of flow range should also consider whether the Reynolds number is within the normal range.
③ Vortex flow meters are not suitable for measuring pulsating flow:
When there are power mechanical equipment such as Roots blower and reciprocating water pump in the pipeline system, strong pulsation will occur. If the pulsation frequency is within the vortex frequency band, measurement errors will occur. When the pulsation is severe, it may not even form a Karman vortex street.
3. Pipe diameter
Vortex flow meters can be installed in two different ways: pipeline type and plug-in type. For pipeline type, the diameter of the pipeline is the same as most other flowmeters, with the smallest being DN15 and the largest being able to reach DN300.
If a larger diameter is required, plug-in installation can be chosen. The maximum range of conventional diameters can reach DN2000, and diameters above DN2000 are supplied according to the agreement.
4. Measurement accuracy
The accuracy of vortex flowmeters also has several levels and is classified according to the measurement medium. The pipeline vortex flowmeter can achieve a measurement accuracy of 1.0 level for liquids and 1.5 level for gases. If it is an plug-in vortex flowmeter, the accuracy can reach levels 1.5 and 2.5.
5. Medium temperature
Generally speaking, it is divided into three ranges: normal temperature, moderate temperature, and high temperature. The temperature range is -40~100 ℃ (normal temperature), 100~250 ℃ (medium temperature), and 100~320 ℃ (high temperature). If the temperature of the on-site medium is higher, such as some superheated steam, it can be measured using an orifice flowmeter.
6. Nominal pressure
Mainly divided by installation method, the main demand in the market is as follows, such as flange clamp type (2.5MPa), flange connection type (1.0/1.6/2.5MPa), and plug-in installation type (1.6MPa/2.5MPa/4.0MPa).
7. Power supply
According to the current market demand, there are mainly+12VDC (three wire pulse output),+24VDC (three wire pulse output and two wire current output) 3.6V lithium batteries, and dual power supply.
8. Output signal
According to the current market demand, there are mainly voltage frequency pulse output, two wire 4-20mA output, and HART output. In addition, some situations may require digital output, and we can also provide RS485 communication through modbus.
9. Installation environment
According to the purpose of vortex flowmeters, the vortex signal output methods are mainly selected as follows:
① When the measured medium is a compressible fluid and there are significant changes in the temperature and pressure of the on-site medium, it is recommended to use a vortex sensor with pulse signal remote transmission and equipped with a flow integrator, pressure transmitter, and temperature transmitter with temperature and pressure compensation;
② The flowmeter is installed indoors in a good environment without the need for remote signal transmission. It only needs to read the flow value on site, and the installation position of the flowmeter is convenient for operation and data reading. It is recommended that users choose a digital vortex flowmeter;
③ When the installation environment of the flowmeter is poor, or the installation location is not convenient for on-site reading of flow values, or centralized management, it is recommended to use sensors with output pulse signals and flow integrators, or vortex street transmitters with 4-20mA standard current output;
④ When it is necessary to observe flow on site and transmit signals remotely, it is recommended to choose a digital vortex street transmitter with 4-20mA output;
⑤ When there is no need for on-site reading and only the standard signal is output remotely, it is recommended to choose a vortex street transmitter with a 4-20mA standard current output.
10. Protection level
The commonly used IP protection levels for vortex street include IP65, IP67, IP68, etc.
(1) IP65 represents protection against dust intrusion and water spray;
(2) IP67 represents protection against dust intrusion and temporary flooding;
(3) IP68 represents protection against dust intrusion and continuous flooding.
In general, the appropriate IP protection level should be selected based on the installation location of the vortex street:
(1) Installed indoors, IP65 is sufficient;
(2) Installed above the outdoor ground, choose a protection level of IP65 or above;
(3) Installed in outdoor trenches below ground level, using IP68 and separate amplifiers to prevent rainwater immersion and damage to the amplifier after rain;
Some flammable and explosive situations should choose explosion-proof vortex flowmeters.
About temperature and pressure compensation
Whether a vortex flowmeter requires temperature and pressure compensation depends on actual needs. If the working condition deviation is not significant or the requirements are not high, temperature and pressure compensation is not necessary. If precise measurement is required, compensation is required. Compensation generally adopts on-site installation of pressure and temperature sensors, and uploads pressure, temperature, and flow data to the PLC for calculation to obtain the standard flow rate.
When measuring gas, it is necessary to compensate for both temperature and pressure. Gases are generally settled based on standard volumetric flow rates, as the flow rate changes when the volumetric flow rate, temperature, or pressure of the gas changes;
When measuring superheated steam, it is necessary to compensate for both temperature and pressure. Steam is generally settled based on mass flow rate, as any change in temperature or pressure results in a change in steam density and mass flow rate;
When measuring saturated steam, single temperature compensation or single pressure compensation is required. The density of saturated steam has a fixed correspondence with temperature or pressure (saturated steam density table), and knowing any of them can determine the density of saturated steam.
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