Fluid Flow Measurement Devices
Fluid Flow Meters measure the amount of liquid, gas, or steam passing through the piping system. Most Fluid Flow Meters are designed to measure the speed of fluid flowing through pipes. They use this information and the internal cross-sectional area of the pipe to calculate the volume. Or the amount of mass of fluid passing through the system in a given period of time (that is, 50 gallons per minute).
Fluid flow meter principle
Principles of mechanics:
- Instruments that belong to this type of principle include differential pressure type and rotor type using Bernoulli’s theorem.
- Impulse type and movable tube type using the momentum theorem.
- Use the direct mass formula of Newton’s second law.
- Target type using the principle of fluid momentum.
- Turbine type using the angular momentum theorem.
- Vortex type and vortex street type using the principle of fluid oscillation.
- Pitot tube type and volume type, weir, trough type, and so on using total static pressure difference.
Principles of Electricity:
Instruments used in this type of principle include electromagnetic, differential capacitive, inductive, strain resistance, etc.
Acoustic principle:
Ultrasonic type is used for flow measurement using acoustic principles. Acoustic type (shock wave type) and so on.
Thermal principle:
There are calorimetric, direct calorimetry, indirect calorimetry, etc., which use thermal principles to measure flow.
Optical principle:
Laser type, photoelectric type, etc. are instruments that belong to this type of principle.
Based on physical principles:
Nuclear magnetic resonance, nuclear radiation, etc. are instruments that belong to this type of principle.
Other principles: There are marking principles (tracing principles, nuclear magnetic resonance principles), related principles, etc.
Extended reading: U-series Liquid Mass Flow Meter | Liquid-slurry flow measure
Fluid flow meter types
- According to the measurement objects, there are two categories: closed pipes and open channels.
- According to the principle of measurement, there are mechanical principles, thermal principles, acoustic principles, electrical principles, optical principles, atomic physics principles, etc.
- According to the purpose of measurement, it can be divided into total measurement and flow measurement. The meters are called total meter and flow meter respectively.
Liquid flow meters can be divided into: anti-corrosion flow meters. Liquid flow meters.. Differential pressure flow meters. Ammonia flow meters. Turbine flow meters. Electromagnetic flow meters. Vortex flow meters in fluid oscillating flow meters. Mass flow meters.
The differential pressure flowmeter is a meter that calculates the flow rate based on the differential pressure generated by the flow detection element installed in the pipeline, the known fluid conditions and the geometric dimensions of the detection element and the pipeline.
The differential pressure flowmeter is composed of a primary device (detection part) and a secondary device (differential pressure conversion and flow display instrument).
Differential pressure flowmeters are usually classified in the form of detection parts, such as orifice flowmeters, venturi flowmeters, and averaging velocity tube flowmeters.
The secondary devices are various mechanical, electronic and electromechanical integrated differential pressure gauges, differential pressure transmitters and flow display instruments.
It has been developed into a large class of instruments with a high degree of three-dimensionalization (serialization, generalization, and standardization) and a large variety of specifications. It can measure flow parameters as well as other parameters (such as pressure, level, density, etc.)
Extended Reading: Advantages and disadvantages of differential pressure flow meter
The detection parts of the differential pressure flowmeter can be divided into several categories according to its principle of action: throttling device, hydraulic resistance type, centrifugal type, dynamic head type, dynamic head gain type and jet flow type.
Differential pressure flow meters are one of the most widely used flow meters. Among all kinds of flow meters, their usage ranks first.
In recent years, due to the advent of various new flowmeters, its usage percentage has gradually decreased, but it is still the most important type of flowmeter.
Extended reading: V-Cone Flow Meter Working Principle
Target flow meters began to be used in industrial flow measurement in the 1960s. It is mainly used to solve the flow measurement of high-viscosity and low-Reynolds number fluids. It has experienced two major development stages of pneumatic meters and electric meters.
SBL series intelligent target flowmeter is based on the measurement principle of the original strain gauge (capacitive) target flowmeter. The latest force sensor is used as the measurement and sensitive transmission element. At the same time, modern digital intelligent processing technology is used. And developed a new type of flow meter.
Positive displacement flow meters, also known as fixed displacement flow meters, or PD flow meters for short. It is the most accurate type of flow meters.
It uses a mechanical measuring element to continuously divide the fluid into a single known volume part. The total volume of the fluid is measured according to the number of times that the measuring chamber is filled with and discharged the volume part of the fluid successively.
Extended reading: Positive Displacement Flow meter Technology
Positive displacement flow meters are classified according to their measuring components and can be divided into oval gear flow meters, scraper flow meters, dual rotor flow meters, rotary piston flow meters, reciprocating piston flow meters, disc flow meters, and liquid-sealed tumbler flow meters. , Wet gas meter and membrane gas meter, etc.
Extended reading: Flow Totalizer F3000X for Data collection and calculation
The turbine flowmeter is the main type of velocity flowmeter. It uses a multi-blade rotor (turbine) to sense the average flow rate of the fluid. It is a meter that derives the flow or total amount from it. Generally, it is composed of two parts, a sensor and a display, and it can also be made into an integral type.
Turbine flowmeters, positive displacement flowmeters, and mass flowmeters are referred to as the three types of flowmeters with high repeatability and high precision, and are one of the top ten types of flowmeters.
An electromagnetic flowmeter is an instrument for measuring conductive liquid made according to Faraday’s law of electromagnetic induction.
The electromagnetic flowmeter has a series of excellent characteristics. It can solve the problems that other flowmeters are not easy to apply, such as the measurement of dirty flow and corrosive flow.
The vortex flowmeter is a meter in which a non-streamlined vortex generator is placed in the fluid. The fluid is alternately separated on both sides of the generator to release two series of regularly staggered vortices.
Vortex flowmeters can be classified into stress type, strain type, a capacitive type, thermal type, vibrating type, photoelectric type, an ultrasonic type according to the frequency detection method.
An ultrasonic flowmeter is a meter that measures the flow rate by detecting the effect of fluid flow on the ultrasonic beam (or ultrasonic pulse).
According to the principle of signal detection, ultrasonic flowmeters can be divided into propagation velocity difference method (direct time difference method, time difference method, phase difference method, and frequency difference method), beam shift method, Doppler method, cross-correlation method, and spatial filtering method And noise law, etc.
Ultrasonic flowmeters are the same as electromagnetic flowmeters. Because there are no obstructions in the flow channel of the instrument, they are non-obstructive flowmeters. They are a type of flowmeter suitable for solving difficult problems in flow measurement. Especially in large-diameter flow measurement.
Extended reading: Make Ultrasonic Open Channel Flow Meter Work for You
Coriolis Mass Flowmeter is a novel instrument that directly and accurately measures the mass flow of fluids. The main structure adopts two U-shaped tubes arranged side by side. The curved parts of the two tubes vibrate slightly towards each other. Then the straight pipes on both sides will follow the vibration. That is, they will move closer or open at the same time. That is, the vibration of the two pipes is synchronized and symmetrical.
If the fluid is introduced into the pipe while the pipe is vibrating synchronously, so that it flows forward along the inside of the pipe, the pipe will force the fluid to vibrate up and down together with it.
The thermal flow meter sensor contains two sensing elements. A speed sensor and a temperature sensor. They automatically compensate and correct for gas temperature changes.
The electric heating part of the instrument heats the speed sensor to a certain value higher than the temperature of the working condition. A constant temperature difference is formed between the speed sensor and the sensor that measures the temperature of the working condition.
When the temperature difference is kept constant, the energy consumed by electric heating, which can be said to be the heat dissipation value, is proportional to the mass flow rate of the gas flowing through.
The rotameter consists of two parts.
One piece of rotameter is a tapered tube that gradually expands from bottom to top.
The other part of the rotameter is a rotor that is placed in a tapered tube and can move freely up and down along the centerline of the tube.
When measuring the flow of fluid, the measured fluid flows in from the lower end of the tapered tube. The flow of the fluid impacts the rotor and generates a force on it (the magnitude of this force varies with the magnitude of the flow).
When the flow is large enough, the generated force will lift the rotor and raise it.
At the same time, the measured fluid flows through the annular section between the rotor and the tapered tube wall.
There are three forces acting on the rotor at this time: the dynamic pressure of the fluid on the rotor, the buoyancy of the rotor in the fluid, and the gravity of the rotor itself.
When the flowmeter is installed vertically, the center of gravity of the rotor coincides with the tube axis of the tapered tube, and the three forces acting on the rotor are all along the direction parallel to the tube axis.
When these three forces reach a balance, the rotor floats smoothly on a certain position in the cone.
For a given rotameter, the size and shape of the rotor have been determined. Therefore, its buoyancy in the fluid and its own gravity are known to be constant. Only the dynamic pressure of the fluid on the float changes with the flow rate of the incoming flow. of.
Therefore, when the flow rate of the incoming flow becomes larger or smaller, the rotor will move up or down. The flow cross-sectional area of the corresponding position also changes. Until the flow rate becomes the corresponding speed when the flow rate becomes balanced, the rotor will be stable in the new position.
For a given rotameter, the position of the rotor in the cone tube is in a one-to-one correspondence with the flow rate of the fluid flowing through the cone tube.
The fluid-filled with the pipe flows through the throttling device in the pipe. It causes local contraction near the throttling piece, and the flow velocity increases. There is a static pressure difference between the upstream and downstream sides.
Under the condition of known relevant parameters, according to the principle of flow continuity and Bernoulli equation, the relationship between differential pressure and flow can be deduced to obtain the flow.
Read more about: Orifice Flow Meter
Different from the previous ones, the open channel flow meter is a flow meter that measures the natural flow of the free surface in a non-full tubular open channel.
The working principle of the open channel flowmeter is to use the open channel technology. By measuring the fluid level height, the flow rate is obtained through the calculation of the internal microprocessor of the instrument.
Because it is a non-contact measurement, the open channel flowmeter can be used in harsher environments.
The open channel flowmeter launches and receives the open channel under the control of the computer.
Calculate the distance between the open channel flowmeter and the measured liquid level according to the transmission time. Thus the liquid level height is obtained. Because there is a certain proportional relationship between the liquid level and the flow rate.
Therefore, the liquid flow rate Q can be finally obtained according to the calculation formula.
Hydraulic fluid flow meter
Industrial Hydraulic oil flow meter, also called hydraulic flow meter gauge. Hydraulic oil flow meters are inline flow meters for hydraulic oil flow measurement.
Sino-Inst offers Turbine, Mass flow, Oval gear, V-cone, Target, and Orifice flow meters for inline hydraulic oil flow. Features like: bidirectional, high pressure, analog, can be customized as customer need.
Extended reading: What Is Hydraulic Flow Meter?
Ultrasonic fluid flow meter
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.
Fluid mass flow meter
Fluid mass flow meter directly measures the mass flow of the medium passing through the flow meter. It can also measure the density of the medium and indirectly measure the temperature of the medium.
A flow measuring instrument that measures the mass flow in the pipeline. The measured fluid is under the condition that the pressure, temperature and other parameters change greatly. If only the volume flow is measured, the change in fluid density will bring about a large measurement error.
In positive displacement and differential pressure flowmeters, the density of the fluid to be measured may vary by 30%, which will cause an error of 30 to 40% in the flow rate.
With the improvement of automation level, many production processes have put forward new requirements for flow measurement. The chemical reaction process is controlled by the quality (not the volume) of the raw materials.
The heating and cooling effects of steam and air flow are also proportional to the mass flow.
The strict control of product quality, accurate cost accounting, and fuel control of airplanes and missiles all require precision. Therefore, the mass flow meter is an important flow measuring instrument.
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Fluid Flow Meters Selection Guide
How to select the flowmeter？
It can be considered from five aspects. These five aspects are flow meter performance, fluid characteristics, installation conditions, environmental conditions and economic factors. The detailed factors in the five areas are as follows:
- Instrument performance: accuracy, repeatability, linearity, range, flow range, signal output characteristics, response time, pressure loss, etc.;
- Fluid characteristics: temperature, pressure, density, viscosity, chemical corrosion, abrasiveness, fouling, miscibility, phase change, electrical conductivity, speed of sound, thermal conductivity, specific heat capacity, isentropic index;
- Installation conditions: pipeline layout direction, flow direction, length of the upstream and downstream side of the test piece, pipe diameter, maintenance space, power supply, grounding, auxiliary equipment (filter, getter), installation, etc.;
- Environmental conditions: ambient temperature, humidity, electromagnetic interference, safety, explosion-proof, pipeline vibration, etc.;
- Economic factors: instrument purchase, installation, operation, calibration, maintenance, instrument service life, spare parts, etc.
The flowmeter selection steps are as follows:
- According to the fluid type and five consideration factors, the available instrument types are initially selected (there are several types for selection);
- Collect data and price information for the primary selection type. Prepare conditions for in-depth analysis and comparison;
- Use the elimination method to gradually concentrate on 1 or 2 types. It is necessary to repeatedly compare and analyze the five factors to finally determine the pre-selection target.
Frequently asked questions
Related fluid flow measurement devices
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Sino-Inst offers over 50 flow meter for flow measurement. About 50% of these are differential pressure flow meters, 40% is the liquid flow sensor, and 20% are Ultrasonic Level Transmitter and mass flow meter.
A wide variety of flow meters options are available to you, such as free samples, paid samples.
Sino-Instrument is a globally recognized supplier and manufacturer of flow measurement instrumentation, located in China.
Wu Peng, born in 1980, is a highly respected and accomplished male engineer with extensive experience in the field of automation. With over 20 years of industry experience, Wu has made significant contributions to both academia and engineering projects.
Throughout his career, Wu Peng has participated in numerous national and international engineering projects. Some of his most notable projects include the development of an intelligent control system for oil refineries, the design of a cutting-edge distributed control system for petrochemical plants, and the optimization of control algorithms for natural gas pipelines.