Classified by measurement method: velocity type (such as vortex flowmeter, vortex flowmeter, turbine flowmeter, ultrasonic flowmeter, etc.); Differential pressure flowmeter (orifice flowmeter, V-cone flowmeter, etc.); Volumetric flow meters (elliptical gear flow meters, Roots flow meters, membrane gas meters, etc.); Mass flow meters (Coriolis mass flow meters, calorimetric mass flow meters, etc.); Open channel flow meter (Bacher trough, triangular weir, etc.)
differential pressure flowmeter
Differential pressure flowmeter is a type of flow meter that calculates the flow rate by measuring the differential pressure generated by the flow detection element installed in the industrial pipeline, taking into account the known fluid conditions and the geometric dimensions of the detection element and pipeline.
The differential pressure flowmeter consists of a primary detection component and secondary instruments (differential pressure converter or transmitter and flow display instrument). Differential pressure flow meters are classified in the form of detection components, including orifice flow meters, Venturi flow meters, and averaging tube flow meters. Secondary instruments include various mechanical, electronic, and electromechanical integrated differential pressure flow meters, differential pressure transmitters, and flow display instruments.
Differential pressure flow meters are the most widely used flow meters in the flow instrument family. Currently, they have been serialized, standardized, and popularized both domestically and internationally. Differential pressure flow meters can measure flow parameters independently, as well as other parameters such as pressure, level, and density. The detection components of differential pressure flow meters can be divided into several categories according to their operating principles, including throttling devices, hydraulic resistance, dynamic head type, dynamic head gain and jet type, and centrifugal type.
There are two main types of test pieces: standardized and non-standard. Standard type detection components are designed, manufactured, installed, and used based on standard documents, without the need for actual flow calibration to determine their flow values and estimate measurement errors. Non standardized detection components are generally not included in international standards for detection components. Differential pressure flowmeter is also the most widely used type of flow meter, occupying the first place in the usage of various flowmeters. The main advantages are: (1) the most widely used orifice plate flowmeter has a sturdy structure, stable and reliable performance, and a long service life; (2) It has a wide range of applications and there is currently no flow meter that can be compared to it; (3) The detection components, transmitters, and display instruments are produced by different manufacturers, facilitating economies of scale production.
The main disadvantages are: (1) generally low measurement accuracy; (2) narrow range, generally only 3:1-4:1; (3) High requirements for on-site installation conditions; (4) High pressure loss (referring to orifice plates, nozzles, etc.).
Positive displacement flowmeter
Positive displacement flowmeter, also known as fixed displacement flowmeter or PD flowmeter, is the most accurate type of flow meter. It uses mechanical measuring elements to continuously divide the fluid into individual known volume parts, and measures the total volume of the fluid based on the number of times the measuring chamber repeatedly fills and discharges that volume part of the fluid.
Volumetric flow meters are classified according to their measuring components, including elliptical gear flow meters, rotary piston flow meters, reciprocating piston flow meters, disc flow meters, wet gas meters and membrane type gas meters, liquid sealed rotary cylinder flow meters, etc.
Main advantages: (1) High measurement accuracy; (2) The installation of pipeline conditions does not affect the measurement accuracy; (3) Can be used for measuring high viscosity liquids; (4) Wide range; (5) Direct reading instruments do not require external energy and can directly obtain cumulative, total, clear, and easy to operate information. Main disadvantages: (1) Complex results and large volume; (2) There are significant limitations in the type, diameter, and working state of the tested medium; (3) Not suitable for high and low temperature environments; (4) Most instruments are only suitable for clean single-phase fluids; (5) Generate noise and vibration.
float flowmeter
Float flowmeter, also known as rotor flowmeter, is a type of variable area flowmeter. In a vertical conical tube that expands from bottom to top, the gravity of the circular cross-section float is supported by liquid dynamics, allowing the float to freely rise and fall inside the conical tube. Float flowmeter is a widely used type of flowmeter after differential pressure flowmeter, suitable for monitoring small flow rates. Main advantages: (1) Simple structure and convenient use; (2) Suitable for small diameters and low flow rates; (3) Low pressure loss. Disadvantages: Low pressure resistance and fragile glass tubes.
Turbine Flowmeter
Turbine flowmeter is a major type of velocity flowmeter, which is composed of a multi blade rotor (turbine) that senses the average fluid velocity and measures the flow rate or total flow rate. Its structure consists of two parts: sensors and displays, with two types: split type and integrated type.
Turbine flow meters, volumetric flow meters, and Coriolis mass flow meters are collectively referred to as the three types of flow meters with the best repeatability and accuracy. At present, it has developed towards multiple varieties and series.
Main advantages: (1) High precision, making it the most accurate flow meter among all flow meters; (2) Good repeatability; (3) No zero drift, good anti-interference performance; (4) Wide measurement range; (5) Compact structure.
Main disadvantages: (1) unable to maintain calibration characteristics for a long time; (2) The physical properties of fluids have a significant impact on flow characteristics.
Vortex flowmeter
The structure of a vortex flowmeter is to place a non streamlined vortex generator in the fluid, and when the fluid alternately separates on both sides of the vortex generator, it releases two series of regularly staggered vortex instruments. Vortex flowmeter is generally classified according to frequency detection methods, including stress type, strain type, capacitance type, thermal sensitive type, photoelectric type, ultrasonic type, vibration type, etc. ）Vortex flowmeter is a new type of flow instrument both domestically and internationally.
Main advantages: (1) Simple and sturdy structure; (2) Suitable for flow rates in situations with multiple fluid types; (3) Has high measurement accuracy; (4) The measurement range is wide and the pressure loss is small.
Main disadvantages: (1) Not suitable for measuring low Reynolds number fluids; (2) Requires a longer straight pipe section; (3) Compared to turbine flow meters, the instrument coefficient is lower.
Electromagnetic Flowmeter
Electromagnetic flowmeter consists of sensors, converters, and displays. It is a general flow meter for measuring conductive fluids made according to Faraday’s law of electromagnetic induction. Electromagnetic flow meters have unique advantages that other flow meters cannot compare to, especially suitable for measuring dirty and corrosive fluids. Electromagnetic flowmeter became a widely used flow monitoring instrument in modern industrial fields in the 1970s and 1980s due to significant technological breakthroughs in electromagnetic flow.
Main advantages: (1) As the measurement channel is a smooth straight pipe, it will not block, making it particularly suitable for liquid-solid two-phase fluids with solid particles, such as pulp, sewage, mud, etc; (2) No pressure loss, good energy-saving effect; (3) Not affected by changes in fluid humidity, density, viscosity, pressure, and conductivity; (4) Large flow range and wide aperture range; (5) Suitable for measuring corrosive fluids.
Main disadvantages: (1) Not suitable for measuring released petroleum product fluids; (2) Not applicable to gases, vapors, and liquids containing large bubbles; (3) Not suitable for high temperature environments.
ultrasonic flowmeter
Ultrasonic flowmeter is designed based on the principle that the speed of ultrasonic propagation 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 velocity. Although ultrasonic flow meters only appeared in the 1970s, they are very popular and have great development prospects because they can be made into non-contact types and can be linked with ultrasonic water level gauges for open flow measurement without causing disturbance or resistance to the fluid.
Classification of Ultrasonic Flowmeters: 1. Doppler Ultrasonic Flowmeters: The transducer 1 emits an ultrasonic signal with a frequency of f1. After passing through suspended particles or bubbles in the liquid in the pipeline, the frequency shifts and is reflected to the transducer 2 at the frequency of f2. This is known as the Doppler frequency difference fd. Assuming the fluid flow velocity is v and the ultrasonic velocity is c, the Doppler frequency shift fd is proportional to the fluid flow velocity v. When the pipeline conditions, transducer installation position, emission frequency, and sound velocity are determined, c, f1, and θ are constants. The fluid flow velocity is proportional to the Doppler frequency shift, and the fluid flow rate can be obtained by measuring the frequency shift. Time difference ultrasonic flowmeter: Time difference ultrasonic flowmeter uses the principle that the time difference between the forward and backward propagation of sound waves in a fluid is proportional to the fluid flow velocity to measure fluid flow rate