What is a velocity flow meter?
Velocity Flow Meter is a flow meter that obtains flow parameters by directly measuring the flow rate of the full pipe in the closed pipe section. The flow rate can be calculated by measuring the velocity of the flow by using a velocity flow meter. Velocity flow meters mainly include-electromagnetic, ultrasonic, turbine, vortex, precessing vortex, rotor, etc.
Flow Meter Types
There are many types of flow meters. Basically, there are the following types of flow meters
Why are there so many types of flow meters? This starts with the working conditions of the factory. The three elements of working conditions, medium, temperature, pressure, and conditions are ever-changing. Create thousands of types of working conditions. It requires different principles and different types of flow meters.
Extended reading: Integral DP Flow Meter|Gas, liquid, steam|Compact structure
Velocity Flow Meter Types
A magnetic Flow Meter is a flow meter that measures the flow of conductive fluids. Abbreviated as EMF, also called Electromagnetic flowmeters. It is a kind of Volumetric flow meter. A magnetic flow meter measures the velocity of conductive liquids moving through a pipe or conduit. In the wastewater treatment industry, a Magnetic Flow Meter is the best flow meter choice.
Advantages of using Electromagnetic Flow Meters.
- High precision and stability
- Self-check
- Two-way measurement
- No pressure loss
- No moving parts
- May be for sanitary purposes
- Large size available
- Dirty liquid and mixed fructose are ok
Disadvantages of using Magnetic Flow Meters
- Can not be used to measure gas, steam and liquids containing a lot of gas;
- Cannot be used to measure liquid media with very low conductivity.
- Cannot be used to measure high temperature media. At present, it is restricted by the lining material and electrical insulation material of the measuring tube of the electromagnetic flowmeter for general industry;
- The electromagnetic flowmeter is easily affected by external electromagnetic interference.
The ultrasonic flow meter measures the liquid flow rate quickly and effectively. There are two types of ultrasonic flowmeter technology: Doppler frequency shift and transit time.
Transit time ultrasonic flow meter is most suitable for measuring the flow of cleaning liquid. Therefore, it is the most popular type of ultrasonic meter.
Doppler ultrasonic flow meter can measure the frequency difference of sound waves reflected from bubbles or particles in the airflow. It is suitable for aerated or dirty liquids.
Advantages of Ultrasonic Flow Meters
- Ultrasonic flowmeter is a non-contact measuring instrument, which can be used to measure the flow of fluids and large pipe diameters that are not easy to contact and observe. It does not change the fluid flow state, does not produce pressure loss, and is easy to install.
- It can measure the flow of strong corrosive media and non-conductive media.
- Ultrasonic flow meters have a large measuring range, with pipe diameters ranging from 20mm to 6m.
- Ultrasonic flowmeter can measure the flow of various liquids and sewage.
- The volume flow measured by the ultrasonic flowmeter is not affected by the temperature, pressure, viscosity and density of the fluid being measured. It can be made into fixed and portable forms.
Disadvantages of Ultrasonic Flow Meters
- The temperature measurement range of an ultrasonic flowmeter is not high, and generally it can only measure fluids with a temperature lower than 200°C.
- Poor anti-interference ability. It is susceptible to the interference of bubbles, fouling, pumps and other sound sources mixed with ultrasonic noise, which affects the measurement accuracy.
- The straight pipe section has strict requirements, 20D in the front and 5D in the back. Otherwise, the dispersion is poor and the measurement accuracy is low.
- Uncertainty in installation will bring large errors to flow measurement.
- The fouling of the measuring pipe will seriously affect the accuracy of the measurement and bring about significant measurement errors. Even in severe cases, the meter has no flow display.
- Reliability and accuracy are not high (generally around 1.0-2.5), and repeatability is poor.
Extended reading: Make Ultrasonic Open Channel Flow Meter Work for You
Turbine flow meters are velocity flow meters, also called impeller flow meters. Can be used to measure the instantaneous flow and cumulative flow of liquids and gases.
Turbine flowmeters are widely used in flow measurement: petroleum, organic liquids, inorganic liquids, liquefied gas, natural gas, coal gas, and cryogenic fluids. Turbine flowmeter signals can be divided into pulse signals or current signals (4-20mA). It is suitable for use with secondary display, PLC, DCS, and other computer control systems.
Turbine Meter Advantages
- The cost is moderate.
- Very good at clean, low viscosity fluids of moderate velocity and a steady rate.
- Turndown is very good as it can read very low compared to the greatest flow.
- They are reliable if put in a clean fluid especially if it has some lubricity.
- AGA and API approved for custody transfers.
- They do cause some pressure drop where that may be a factor such as gravity flows.
- High accuracy. Among all flowmeters, it is the most accurate flowmeter.
- No zero drift, good anti-interference ability.
- High accuracy. Among all flowmeters, it is the most accurate flowmeter.
- No zero drift, good anti-interference ability.
Turbine Meter Disadvantages
- Not reliable for steam.
- Bearings wear out.
- Requires constant backpressure to prevent cavitation.
- Accuracy adversely affected by bubbles in liquids.
- Turbine meters can be used with clean liquids and gases only (may need to install a strainer upstream to prevent damage from particulates).
- Not applicable for measuring corrosive fluids.
- May not function properly with high viscosity fluids where the flow profile is laminar.
- Cannot maintain calibration characteristics for a long time.
Extended reading: Turbine Insertion Flow Meter for Large Diameter Pipeline
A vortex flow meter is also called Vortex shedding flow meter. Vortex Flow Meter is suitable for flow measurement of steam and various liquids and gases.
The vortex flowmeter is a volume flow meter that measures the volume flow of gas, steam, or liquid, the volume flow of standard conditions, or the mass flow of gas, steam, or liquid-based on the Karman vortex principle. When the fluid flows through the dust collector rod of the vortex flowmeter, a vortex is formed. The frequency of vortex shedding is proportional to the fluid velocity. Temperature and pressure compensation can be configured.
Extended reading: Vortex Steam Flow Meter
Advantages of vortex flowmeter
- The pressure loss is small, about 1/4 to 1/2 of the throttling differential pressure flowmeter.
- Output a pulse signal proportional to the flow rate, without zero drift.
- The structure is simple, firm, easy to install and maintain. There is no need for pressure guiding pipe and three-valve group, etc., reducing leakage, blockage and freezing. The measuring element has simple structure, reliable performance and long service life.
- The accuracy is high, generally ±(1～1.5)%R.
- The measuring range is wide, the vortex flowmeter with a reasonable caliber is determined, and the range can reach 20:1.
- Within a certain Reynolds number range, the output frequency of the orifice flowmeter is not affected by the physical properties (density, viscosity) and composition of the fluid, that is, the meter coefficient is only related to the shape and size of the vortex generator and the pipeline.
- The volume flow of the vortex flowmeter is not affected by thermal parameters such as the temperature, pressure, density or viscosity of the fluid being measured. Generally, no separate calibration is required. It can measure the flow of liquid, gas or steam.
Understanding the relationship between Flow Rate and Pressure may help you calculate mass or volume flow.
Disadvantages of vortex flowmeter
(1) The volume flow of the vortex flowmeter is not affected by the temperature, pressure, density and other thermal parameters of the measured fluid, but the final measurement result of liquid or steam should be the mass flow. For gas, the final measurement result Should be the standard volume flow. Both the mass flow rate or the standard volume flow rate must be converted by fluid density, and changes in fluid density caused by changes in fluid working conditions must be considered.
(2) The main factors that cause flow measurement errors are: measurement errors caused by uneven flow velocity of the pipeline; the density of the medium when the fluid working condition changes cannot 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 very large.
(3) Poor vibration resistance. External vibration will cause measurement errors of the vortex flowmeter, or even fail to work normally. The high-velocity impact of the channel fluid will cause additional vibration to the cantilever of the vortex generator, which will reduce the measurement accuracy. The influence of large pipe diameter is more obvious.
(4) Poor adaptability to measuring dirty media. The generating body of the vortex flowmeter is very easy to be dirty by the medium or entangled by the dirt, and the change of the geometric body size has a great influence on the measurement accuracy.
(5) High requirements for straight pipe sections. Experts pointed out that the straight pipe section of the vortex flowmeter must ensure the front 40D and the 20D to meet the measurement requirements.
(6) Poor temperature resistance. Vortex flowmeters generally can only measure the fluid flow of media below 300°C.
Extended Reading: Collection of Industrial Insertion Flowmeter Type
More about Different Types of Flowmeters – Technical and Application Analysis.
Area Velocity Flow Meter
Variable area flow meters are flow meters in which the fluid must pass through a restricted area. Because the flow cross-sectional area of the flow meter varies with the height of the float. Therefore, this type of flowmeter is called variable area flowmeter or equal pressure drop flowmeter. The typical instrument of this type of flowmeter is a rotameter. This is in contrast to flow meters such as orifice plates and venturi tubes, where the area of the flow element remains fixed. Variable area flowmeters can measure of gas and fluid flow.
Variable area flow meter advantages and disadvantages
- The advantages of the variable area flow meter are simple structure and easy testing, suitable for measuring small flow.
- The disadvantage of variable area flow meter is that it is easily affected by factors such as fluid density, pressure, and viscosity. When testing the flue gas flow, because the flue gas contains dust, the area flowmeter cannot be used.
Extended reading: Fuel Flow Meter for Boat-Selection & Application
Mechanical Flow Meter
Mechanical flow meters are a type of flow meters that use arrangement moving parts to measure flow. The fluid passes through a series of gears or chambers (positive displacement or PD) or through a rotating turbine or rotor. Mechanical flowmeter is different from electromagnetic and ultrasonic in principle. Mechanical flow meters easily monitor liquid flow rates for water, fuels, viscous fluids and more.
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Extended reading: Mechanical flow meter types
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Extended Reading: Inline Ultrasonic Flow Meter
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