Flowmeter classification and working principle

1. Classification of flow meters

According to the measurement principle, there are: mechanics principle, thermal principle, acoustic principle, electrical principle, optical principle, atomic physics principle, etc.

According to the structure principle of the flowmeter, it is divided into: positive displacement flowmeter, differential pressure flowmeter, float flowmeter, turbine flowmeter, electromagnetic flowmeter, vortex flowmeter in fluid oscillating flowmeter, mass flowmeter and plug-in type Flow meter, probe flow meter.

Second, the working principle and application of ordinary flow meters

1. Differential pressure flow meter

The differential pressure flowmeter is a meter that calculates the flow rate based on the pressure difference generated by the flow detection component installed in the pipeline, the known fluid state, and the overall size of the detection component and the pipeline.

Application: Differential pressure flowmeter has a wide range of applications. It can be applied to various objects in closed pipeline flow measurement, such as fluid: single-phase, mixed-phase, clean, dirty, viscous flow, etc.; working mode: normal pressure, high pressure, vacuum, normal temperature, high temperature, low temperature, etc.; pipe diameter : From a few millimeters to a few meters; Flow: subsonic, sound waves, pulsating flow. Its use in various industrial fields accounts for about 1/4 to 1/3 of the total flow meters.

2. Float flow meter

Float flowmeter, also called rotameter, is a variable area flowmeter. In the vertical cone that expands from the bottom to the top, the gravity of the circular cross-section float is absorbed by the hydrodynamic force, so that the float can rise and fall freely within the cone.

Application: The float flowmeter is a widely used flowmeter after the differential pressure flowmeter, especially for small and micro flow.

3. Volume flow meter

Volumetric flow meters, also known as fixed displacement flow meters, and PD flow meters, are the most accurate type of flow meters. Based on the measurement results, it uses mechanical measurement components to continuously divide the fluid into a single known volume fraction. The chamber is repeatedly filled and multiple volumes of fluid are discharged to measure the total volume of the fluid.

Application: Positive displacement flow meters, differential pressure flow meters and float flow meters are listed as the three largest flow meters. They are usually used for total measurement of expensive media (oil, natural gas, etc.).

4. Turbine flowmeter

Turbine flow meters are the main type of velocity flow meters, which use multi-blade rotors (turbines) to sense the average flow rate of the fluid and obtain the flow or total amount. Usually, it consists of two parts, the sensor and the display instrument, and it can also be made into a single type.

Application: Turbine flowmeters are widely used in the measurement of petroleum, organic liquids, inorganic liquids, liquefied gases, natural gas and cryogenic fluids.

5. Electromagnetic flowmeter

Electromagnetic flowmeter is a meter that measures conductive liquids according to Faraday's law of electromagnetic induction.

Application: Electromagnetic flowmeter has a series of excellent characteristics, which can solve the problems of other difficult-to-use flowmeters, such as the measurement of dirty flow and corrosion flow. Electromagnetic flowmeters are widely used in applications. Large-caliber instruments are widely used in water supply and drainage projects. Small and medium-sized calibers are usually used in high-demand or difficult-to-measure applications, such as the cooling water control of blast furnace tuyere in the steel industry, the measurement of pulp and black liquor in the paper industry, and the strong chemical industry. Corrosive liquid, non-ferrous metallurgical industry pulp; small diameter, small diameter is often used in the medical industry, food industry, biochemistry and other places with sanitary requirements.

6. Vortex flowmeter

Application: The vortex flowmeter has developed rapidly and has become a general-purpose flowmeter.

7. Ultrasonic flowmeter

The ultrasonic flowmeter is designed based on geometric principles, that is, the speed of the ultrasonic wave propagating in the flowing medium is equal to the average flow velocity of the measured medium and the speed of the sound wave itself. It also reflects the flow rate by measuring the flow rate. According to the measurement principle, ultrasonic flowmeter can be divided into time difference type and Doppler type.

Application: The propagation time method for cleaning single-phase liquids and gases. Typical applications include factory wastewater, exotic liquids, liquefied natural gas, etc.; natural gas applications have rich experience in the field of high-pressure natural gas; Doppler method is suitable for two-phase fluids with low multiphase content, such as untreated sewage, factory wastewater, Dirty process fluids are generally not suitable for very clean liquids.

8. Mass flow meter

Mass flow meters are available in direct and indirect versions. The direct mass flow meter uses the principle directly related to the mass flow rate to measure; the indirect mass flow meter uses the density meter to indirectly multiply the volume flow rate to obtain the mass flow rate.

Application: Under the conditions of high temperature and high pressure in modern industrial production, the application of direct mass flowmeter is very difficult due to material and structure reasons, while indirect mass flowmeter is limited by humidity and pressure range. This is not practical either.

9. Plug-in flowmeter

The working principle of the plug-in flowmeter is based on Faraday's law of electromagnetic induction. In the electromagnetic flowmeter, the conductive medium in the measuring tube is equivalent to the conductive metal rod in the Faraday test, and the two electromagnetic coils at the upper and lower ends generate a constant magnetic field. When the conductive medium flows, an induced voltage is generated. Two electrodes in the pipe measure the induced voltage generated. The measuring tube is electromagnetically isolated from the fluid and the measuring electrode by a non-conductive lining (rubber, Teflon, etc.).

Applications: power generation and combined heat and power, heating industries; aviation, aerospace, shipbuilding, nuclear energy and weapons industries; machinery, metallurgy, coal mining and automobile manufacturing; petroleum and chemical industries; pharmaceutical, food and smoke manufacturing; agriculture and light industry.

10. Probe flowmeter

The basic principle of the probe flowmeter is to transmit the total static pressure to the differential pressure and pressure sensor through the probe hole and the pressure pipe. As long as the probe hole is not blocked, even if there is debris or dirt, pressure can be accurately transmitted. Does not affect accuracy. Since the medium in the pressure guiding tube does not flow, it is difficult for foreign objects to enter and block, so the high precision can be maintained for a long time.

Application: a wide range of applications. 1. A wide range of media: water vapor (saturated, overheated), air, gas, natural gas, various chemical raw materials, liquids, water, various solutions, oil, etc. can be measured; the medium temperature can be as high as 650 degrees Celsius, and the maximum pressure can be Up to 25Mpa. Secondly, the applicable flow range is very wide: the minimum flow rate of the medium can be measured as 0.1 tons/hour, and the maximum measurable value is 5,000 tons/hour. Third, it is suitable for various cross-sectional shapes of the medium pipe: the flow meter does not require the cross-sectional geometry of the medium pipe, such as round, oval, square, rectangular, rhombus, etc.