The English name of a flowmeter is flowmeter, which is defined by the National Science and Technology Terminology Review Committee as an instrument that indicates the measured flow rate and/or the total amount of fluid within a selected time interval. Simply put, it is an instrument used to measure fluid flow in pipelines or open channels.
Flow meters are divided into differential pressure flow meters, rotor flow meters, throttling flow meters, narrow slit flow meters, volumetric flow meters, electromagnetic flow meters, ultrasonic flow meters, etc. Classified by medium: liquid flowmeter and gas flowmeter.
Measurement is the eye of industrial production. Flow measurement is one of the components of measurement science and technology, which is closely related to the national economy, national defense construction, and scientific research. Doing this job well plays an important role in ensuring product quality, improving production efficiency, and promoting the development of science and technology, especially in today's era of energy crisis and increasing industrial production automation. The position and role of flow meters in the national economy are even more prominent.
The commonly used unit in engineering is m3/h, which can be divided into instantaneous flow rate (Flow Rate) and cumulative flow rate (Total Flow). Instantaneous flow rate refers to the amount of effective cross-section that passes through a closed pipeline or open channel per unit time, and the substances flowing through can be gas, liquid, or solid; Accumulated flow refers to the cumulative amount of fluid flowing through the effective cross-section of a closed pipeline or open channel during a certain time interval (one day, one week, one month, one year). The cumulative flow can also be obtained by integrating the instantaneous flow rate with time, so the instantaneous flow meter and the cumulative flow meter can also be compared

development

Coriolis
Coriolis Mass Flow Meter (CMF) is a direct mass flow meter that utilizes the principle of Coriolis force, which is proportional to the mass flow rate, generated when fluid flows in a vibrating tube. [2]
The application of CMF in China started relatively late, and several manufacturing plants have independently developed and supplied the market; Several manufacturing plants have formed joint ventures or adopted foreign technology to produce a series of instruments.
More than 30 series of CMF have been developed abroad, with a focus on technological innovation in the design of flow detection and measurement tube structures, improving instrument zero stability and accuracy, and other performance; Increase the deflection of the measuring tube, improve sensitivity: improve the stress distribution of the measuring tube, reduce fatigue damage, strengthen the ability to resist vibration interference, etc.
Some manufacturers have developed Coriolis instruments that can measure gas-liquid two-phase flow, which can be applied in situations where traditional instruments cannot work, such as unloading ships and media containing bubbles. At the same time, there is an MVD transmitter that can achieve online self calibration of instruments, which does not require disassembling the flow meter. By checking the rigidity of the flow tube, the performance of on-site instruments can be determined.
electromagnetism
Since EMF entered industrial applications in the early 1950s, its usage areas have been expanding day by day. Since the late 1980s, it has accounted for 16% to 20% of the sales revenue of flow meters in various countries.
China has developed rapidly, with an estimated sales of 6500 to 7500 units in 1994. The largest EMF with a diameter of 2-6m has been produced domestically, and the equipment has the ability to verify the diameter of 3m in real flow. In 2008, the sales volume had reached 77 million US dollars, with an estimated sales volume of over 350000 units.
vortex street
USF entered industrial applications in the late 1960s and has accounted for 4% to 6% of the sales revenue of flow meters in various countries since the late 1980s. In 1992, the estimated global sales volume was 35.48 million units, while the estimated domestic products during the same period were between 8000 and 9000 units.

application area

The application of flow measurement technology and instruments can be roughly divided into the following fields.
Industrial Production
Flow meters are one of the major categories of instruments and devices in process automation. They are widely used in various fields of the national economy, such as metallurgy, power, coal, chemical, petroleum, transportation, construction, textiles, food, medicine, agriculture, environmental protection, and people's daily lives. They are important tools for developing industrial and agricultural production, saving energy, improving product quality, enhancing economic efficiency and management level, and occupy an important position in the national economy. In process automation instruments and devices, flow meters have two main functions: as detection instruments for process automation control systems and as total quantity meters for measuring material quantities.
energy metering
Energy is divided into primary energy (coal, crude oil, coalbed methane, petroleum gas, and natural gas), secondary energy (electricity, coke, artificial gas, refined oil, liquefied petroleum gas, steam), and energy carrying working fluids (compressed air, oxygen, nitrogen, hydrogen, water), etc. Energy metering is an important means of scientifically managing energy, achieving energy conservation and consumption reduction, and improving economic efficiency. Flow meters are an important component of energy metering instruments. Commonly used energy sources such as water, artificial gas, natural gas, steam, and oil all use an extremely large number of flow meters, which are indispensable tools for energy management and economic accounting.
environmental protection
The discharge of smoke, waste liquid, sewage, etc. seriously pollutes the atmosphere and water resources, posing a serious threat to the human living environment. The country has made sustainable development a national policy, and environmental protection will be the biggest issue of the 21st century. To control the pollution of air and water, it is necessary to strengthen management, and the basis of management is the quantitative control of pollution. Flow meters play an irreplaceable role in measuring the flow of flue gas emissions, sewage, and exhaust gas treatment.
China is a country that relies mainly on coal as its energy source, with millions of chimneys continuously emitting smoke into the atmosphere. Smoke emission control is an important project to eradicate pollution. Each chimney must be equipped with smoke analysis instruments and flow meters to form a continuous emission monitoring system. The flow rate and volume of flue gas pose significant challenges, including large and irregular chimney sizes, variable gas composition, wide flow velocity ranges, dirt, dust, corrosion, high temperatures, and the absence of straight pipe sections.
Transportation
There are five ways: railway, road, air, water, and pipeline transportation. Although pipeline transportation has long existed, its application is not widespread. With the prominent environmental issues, the characteristics of pipeline transportation have attracted people's attention. Pipeline transportation must be equipped with flow meters, which are the eyes of control, distribution, and scheduling, as well as essential tools for safety monitoring and economic accounting.

Common types:

There are many types of flow measurement methods and instruments, and there are also many classification methods. Before 2011, there were as many as 60 types of flow meters available for industrial use. The reason why there are so many varieties is that none of them are suitable for any fluid, anyrangeA flow meter that is applicable to any flow state and any usage condition, but with the progress of the times, in this era of technological explosion, a latest product has finally emerged-Mass flowmeterMass flow meters are suitable for any fluid, any range, any flow state, and any usage conditions, but they are relatively expensive and cannot be widely used in all industries.

There are over 60 types of old-fashioned flow meters, each with its specific applicability and limitations. According to the measurement object, there are two main categories: closed pipelines and open channels; According to the measurement purpose, it can be divided into total measurement and flow measurement, and their instruments are called total meter and flow meter respectively.
In addition, according to the measurement principle, it can be divided into the following categories:
1. Mechanics principle: Instruments belonging to this type of principle include differential pressure type and rotor type using Bernoulli's theorem; The impulse equation and movable tube equation using the momentum theorem; Using the direct mass formula of Newton's second law; Target based on the principle of fluid momentum; Turbine type using the angular momentum theorem; Vortex type and vortex street type utilizing the principle of fluid oscillation; Utilize pitot tube type, volumetric type, weir, trough type, etc. that utilize the total static pressure difference.
2. Electrical principles: Instruments used for this type of principle include electromagnetic, differential capacitive, inductive, strain resistance, etc.
3. Acoustic principles: There are ultrasonic and acoustic (shock wave) methods that use acoustic principles for flow measurement.
4. Thermal principles: There are various methods for measuring flow using thermal principles, such as calorimetry, direct calorimetry, indirect calorimetry, etc.
5. Optical principles: Laser and photoelectric instruments belong to this type of principle.
6. Atomic physics principles: Nuclear magnetic resonance, nuclear radiation, and other instruments belong to this type of principle
7. Other principles include labeling principles (tracing principles, nuclear magnetic resonance principles), related principles, etc.
This article elaborates on the principles, characteristics, application overview, and domestic and international applications of various flow meters according to the most popular and widely used classification methods currently available
target-type
Target flowmeter is a type of flowmeter based on mechanical principles, which has been developed and applied in industry for decades. The new SBL target flowmeter is a new type of capacitive force induction flowmeter developed on the basis of traditional target flowmeters with the development of new sensors and microelectronics technology. It has the characteristics of no movable parts such as orifice plates and vortex street flowmeters, as well as high sensitivity, accuracy comparable to volumetric flowmeters, and a wide range of measurement. [3]
China developed electric and pneumatic target flow transmitters in the 1970s, which are detection instruments for electric and pneumatic unit combination instruments. Due to the direct use of differential pressure transmitters in force converters at that time, this type of flowmeter inevitably brought many defects caused by the force balancing mechanism itself, such as easy drift of the zero position, low measurement accuracy, and poor reliability of the lever mechanism. Due to the poor performance of the force balance mechanism, many advantages of the target flowmeter itself have not been effectively utilized, and the negative impression of the old target flowmeter by users has not been eliminated to this day.
The force converter of the new SBL target flowmeter adopts a strain type force converter, which completely eliminates the disadvantages of the force balance mechanism mentioned above. The new target flowmeter also applies microelectronics and computer technology to the signal converter and display part. The flowmeter has a series of advantages and is believed to play an important role in many flowmeters in the future.
Differential pressure type
Differential pressure flowmeter is an instrument that calculates flow based on the differential pressure generated by the interaction between the flow detection component installed in the pipeline and the fluid, known fluid conditions, and the geometric dimensions of the detection component and the pipeline.
The differential pressure flowmeter consists of a primary device (detection component) and a secondary device (differential pressure converter and flow display instrument). Differential pressure flow meters are usually classified in the form of detection components, such as orifice flow meters, Venturi flow meters, and averaging tube flow metersPitot tube principle - Bitoba flowmeterWait.
The secondary device includes various mechanical, electronic, and electromechanical integrated differential pressure gauges, differential pressure transmitters, and flow display instruments. It has developed into a large category of instruments with a high degree of standardization (serialization, generalization, and normalization) and a wide range of types and specifications. It can measure both flow parameters and other parameters (such as pressure, level, density, etc.).
The detection components of differential pressure flow meters can be divided into several categories according to their operating principles: throttling device, hydraulic resistance type, centrifugal type, dynamic pressure head type, dynamic pressure head gain type, and jet type.
Testing items can be divided into two categories based on their standardization level: standard and non-standard.
The so-called standard test piece is designed, manufactured, installed, and used according to standard documents, without the need for actual flow calibration to determine its flow value and estimate measurement errors.
Non standard testing components are those with poor maturity and have not yet been included in international standards. Differential pressure flowmeter is the most widely used type of flowmeter, with its usage ranking first among various flow meters. Due to the emergence of various new types of flow meters, their usage percentage has gradually decreased, but they are still the most important type of flow meter at present.
Selection:
General selection
It can be considered from five aspects, including the performance of flow meters, fluid characteristics, installation conditions, environmental conditions, and economic factors. The detailed factors of the five aspects are as follows:
In terms of instrument performance: accuracy, repeatability, linearity, range, flow range, signal output characteristics, response time, pressure loss, etc;
In terms of fluid characteristics: temperature, pressure, density, viscosity, chemical corrosion, abrasiveness, scaling, phase mixing, phase change, conductivity, sound velocity, thermal conductivity, specific heat capacity, isentropic index;
In terms of installation conditions: pipeline layout direction, flow direction, length of straight pipe sections on the upstream and downstream sides of the detection component, pipeline diameter, maintenance space, power supply, grounding, auxiliary equipment (filters, dampers), installation, etc;
In terms of environmental conditions: temperature, humidity, electromagnetic interference, safety, explosion prevention, pipeline vibration, etc;
In terms of economic factors: instrument purchase cost, installation cost, operation cost, calibration cost, maintenance cost, instrument service life, spare parts, etc.
（2） The steps for selecting flow meters and instruments are as follows:
1. Preliminary selection of available instrument types based on fluid types and five factors to consider (there should be several types for selection);
2. Collect data and price information for preliminary selection types to prepare conditions for in-depth analysis and comparison;
3. Using the elimination method, gradually concentrate on 1-2 types, and repeatedly compare and analyze five factors to ultimately determine the pre selection target.
precautions
Fluid characteristics mainly refer to the pressure, temperature, density, viscosity, compressibility, etc. of gas. As the volume of gas varies with temperature and pressure, compensation and correction should be considered.
Instrument performance refers to the accuracy, repeatability, linearity, range ratio, pressure loss, initial flow rate, output signal, and response time of the instrument. When selecting a flowmeter, careful analysis and comparison of the above indicators should be carried out to select an instrument that can meet the flow requirements of the measuring medium.
The installation conditions refer to the flow direction of gas, the direction of the pipeline, the length and diameter of the upstream and downstream straight pipes, the spatial position, and the fittings, all of which will affect the accurate operation, maintenance, and service life of the gas flow meter.
Economic factors refer to purchase costs, installation costs, maintenance costs, calibration costs, and spare parts, which are also affected by the performance, reliability, and lifespan of gas flow meters.
The accuracy level and function of the instrument are selected based on measurement requirements and usage scenarios to achieve cost-effectiveness. For example, in situations such as trade settlement, product handover, and energy measurement,
When selecting precision levels such as 1.0, 0.5, or higher for process control, different precision levels should be chosen according to control requirements. In some cases where only the process flow rate needs to be detected without precise control and measurement, a slightly lower accuracy level, such as 1.5, 2.5, or even 4.0, can be selected. In this case, a low-cost plug-in electromagnetic flowmeter can be used to measure the medium flow rate, instrument range, and diameter measurement of general media. The full flow rate of the electromagnetic flowmeter can be selected within a wide range of 0.5-12m/s for measuring medium flow rate. The selection of instrument specifications (diameter) may not necessarily be the same as the process pipeline, and should be determined based on whether the measured flow range is within the flow rate range. That is, when the pipeline flow rate is too low to meet the requirements of the flow instrument or the measurement accuracy cannot be guaranteed at this flow rate, the instrument diameter needs to be reduced in order to increase the flow rate inside the pipeline and obtain satisfactory measurement results.