Classification of flow meters

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

According to the structure and principle of the flowmeter, it is divided into a positive displacement flowmeter, differential pressure flowmeter, float flowmeter, turbine flowmeter, electromagnetic flowmeter, vortex flowmeter fluid oscillation flowmeter, mass flowmeter and insertion flowmeter, and probe flowmeter.

The working principle and application of commonly used flow meters

1. Differential pressure flowmeter

The differential pressure flowmeter is an instrument that calculates the flow rate based on the differential pressure generated by the flow detection device installed in the pipeline, known fluid conditions, and the combined size of the detection device and the pipeline.

Application: The differential pressure flowmeter has a wide range of applications, and various objects are used in the flow measurement of closed pipelines, such as fluid: single-phase, mixed-phase, clean, dirty, viscous flow, etc.; work: normal pressure, High pressure, vacuum, normal temperature, high temperature, low temperature, etc.; pipe diameter: from a few millimeters to several meters; flow: subsonic, sonic, pulsating flow, etc. Its consumption in various industrial sectors accounts for about 1/4 to 1/3 of the total consumption of flowmeters.

2. Rotameter

Rotameter, also known as rotameter, is a kind of variable area flowmeter. In a vertical conical tube that expands from bottom to top, the gravity of the float with a circular cross-section is borne by the liquid power, so that the float can Rise and fall freely in the conical tube.

Application: Rotameter is the most widely used type of flowmeter after differential pressure flowmeter, especially in small and microflow.

3. Positive displacement flowmeter

A volumetric flowmeter, also known as a fixed displacement flowmeter, or PD flowmeter for short, is the most accurate type of flow meter. It uses mechanical measuring elements to continuously divide the fluid into individual known volume parts. According to the measurement, The total volume of fluid is measured by the number of times the chamber is repeatedly filled and drained with that volume of fluid.

Application: Positive displacement flowmeter, differential pressure flowmeter, and rotameter are listed as the three most widely used flowmeters, and are often used in the total measurement of expensive media (oil, natural gas, etc.).

4. Turbine flowmeter

A turbine flowmeter is the main type of velocity flowmeter. It uses a multi-blade rotor (turbine) to sense the average flow velocity of the fluid and then derives the flow or total amount of the instrument. Generally, it consists of two parts, the sensor, and the display instrument, and it can also be made into an integral type.

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

5. Electromagnetic flowmeter

An electromagnetic flowmeter is an instrument for measuring conductive liquids made according to Faraday's law of electromagnetic induction.

Application: The electromagnetic flowmeter has a series of excellent characteristics, which can solve problems that other flowmeters are not easy to apply, such as the measurement of dirty flow and corrosion flow. Electromagnetic flowmeters have a wide range of applications, and large-caliber instruments are mostly used in water supply and drainage projects; small and medium-caliber meters are often used in high-demand or difficult-to-measure occasions, such as the control of cooling water at blast furnace tuyeres in the iron and steel industry, the measurement of pulp and black liquor in the paper industry, and the strong flow in the chemical industry. Corrosion liquid, ore slurry in the non-ferrous metallurgical industry; small-caliber and micro-caliber are often used in the pharmaceutical industry, food industry, biochemistry, and other places with hygienic requirements.

6. Vortex flowmeter

The vortex flowmeter is an instrument that places a non-streamlined vortex generator in the fluid, and the fluid separates alternately on both sides of the generator to release two strings of regularly staggered vortices. When the flow cross-section is constant, the flow velocity is proportional to the guide volume flow. Therefore, the flow rate can be measured by measuring the oscillation frequency.

Application: The vortex flowmeter has developed rapidly and has become a general type of flowmeter at present.

7. Ultrasonic flowmeter

Ultrasonic flowmeters are designed based on the principle that the speed of ultrasonic waves propagating in a flowing medium is equal to the geometric sum of 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. Ultrasonic flowmeters can be divided into time difference type and Doppler type according to the measurement principle.

Application: The transit time method is applied to clean, single-phase liquids and gases. Typical applications include factory discharge liquid, strange liquid, liquefied natural gas, etc.; gas applications have good experience in the field of high-pressure natural gas; the Doppler method is suitable for two-phase fluids with low heterogeneous content, such as untreated sewage, Plant effluents, dirty process fluids, generally not suitable for very clean fluids.

8. Mass flow meter

There are two types of mass flow meters, direct and indirect. The direct mass flowmeter uses the principle directly related to the mass flow to measure; the indirect mass flowmeter uses the density meter and the volume flows to multiply indirectly to obtain the mass flow.

Application: In the case of high temperature and high pressure in modern industrial production, due to material and structure reasons, the application of direct mass flowmeters encounters difficulties; while indirect mass flowmeters are limited by the range of humidity and pressure due to density, is not good for practical application.

9. Insertion type flow meter

The working principle of the insertion 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 a conductive medium flows, an induced voltage is generated. Two electrodes inside the pipe measure the induced voltage generated. The measuring pipe is electromagnetically isolated from the fluid and the measuring electrode by a non-conductive lining (rubber, Teflon, etc.).

Application: power generation and combined heat and power, heating industry; aviation, aerospace, shipbuilding, nuclear energy, and weapon industry; machinery, metallurgy, coal mine, and automobile manufacturing industry; petroleum and chemical industry; pharmaceutical, food, and smoke manufacturing industry; forest industry, Land reclamation, and light industry, etc.

10. Probe-type flowmeter

The basic principle of the probe flowmeter is to transmit the total and static pressure to the differential pressure and pressure sensor through the probe hole and the pressure guide tube. Accuracy is not affected. Because the medium in the pressure guiding tube does not flow, it is not easy for debris to enter and block, so it can maintain high precision for a long time.

Application: Wide range of applications. One is a wide range of applicable media: water vapor (saturated, superheated), air, gas, natural gas, various chemical materials, liquid, water, various solutions, oil, etc. can be measured. The maximum temperature of the medium is 650 degrees Celsius, and the highest pressure is available for 25Mpa. Second, the applicable flow range is wide: the medium flow can be measured at a minimum of 0.1 tons/hour and a maximum of 5,000 tons/hour. Third, it is applicable to a wide range of cross-sectional shapes of medium pipes: the flowmeter has no requirements on the geometric shapes of medium pipe cross-sections, such as circles, ellipses, squares, rectangles, rhombus, etc. are applicable.