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Doppler ultrasonic flowmeter uses acoustic Doppler principle to measure liquid flow
2012-3-5 9:18:26

First, the measurement principle of Doppler ultrasonic flowmeter
采用声学多普勒原理测量液体流量,即可测量多相流(污浊的液体,如市政污水、工业废水、原油、油水混合物、泥浆、矿浆、纸浆、果汁等),又可测量单相流(较纯净的液体,如自来水、江河原水、海水、化工液体等),应用范围较为广泛。 The Doppler ultrasonic flowmeter uses the acoustic Doppler principle to measure liquid flow, which can measure multiphase flow (fouling liquids, such as municipal sewage, industrial wastewater, crude oil, oil-water mixture, mud, pulp, pulp, juice, etc.), and It can measure single-phase flow (pure liquid, such as tap water, river water, seawater, chemical liquid, etc.), and has a wide range of applications.
When measuring multiphase flow, because the liquid contains reflective particles such as bubbles, solid particles, suspended matter, etc., the Doppler signal is a relatively narrow frequency band velocity. When it is a certain average value (sufficient straight pipe section can ensure its velocity More stable distribution), you can get higher measurement accuracy.
When measuring single-phase flow, the liquid contains fewer reflective particles. At this time, compared with the Doppler signal when measuring multi-phase flow, there is a big difference.
Generally, when a clean liquid flows through an elbow, tee, or half-open valve, the flow velocity distribution is turbulent and turbulent, which is called a turbulent state; when passing through a straight pipe section, the flow rate tends to stabilize. In this way, the interface is generated during the turbulent to stable flow. This interface is called the pressure interface or the shear wave interface. Near the elbow, tee, half-open valve, etc. (1 to 2 times the length of the inner diameter of the pipe), the speed of this interface is unstable. When leaving the elbow, tee, half-open valve, etc. (4 to 5 times the length of the inner diameter of the pipe), the interface flow rate is basically the same as the average flow velocity of the fluid. When leaving more than 10 times the length of the inner diameter of the pipe, this interface disappears and becomes a stable flow velocity distribution.
When measuring single-phase flow, the measurement point can be selected at a length of 4 to 5 times the inner diameter of the pipeline. At this time, the Doppler signal can be obtained at the pressure interface. 测量单相流时的测量精度。 However, this signal is weak and the frequency band is wide. It is necessary to make a special spectrum analysis circuit and amplifying operation circuit to ensure the measurement accuracy of the Doppler ultrasonic flowmeter when measuring single-phase flow.

2. Main application areas [(a) industry, (b) purpose]
(1) Sewage
(A) Sewage treatment plant
(B) Flow measurement at water inlet and outlet and intermediate links
(2) Crude oil
(A) Oilfield
(B) Crude oil, oil-water mixture and oily sewage flow measurement.
(3) Sodium aluminate solution
(A) Aluminum plant
(B) Process flow measurement that cannot be measured by other flowmeters such as sodium aluminate solution
(4) Industrial water and drainage
(A) Steelmaking, ironmaking, chemical, pharmaceutical, papermaking and other plants
(B) Inspection of pump power, effective distribution management of flow in each process, and measurement of total discharge outlet
(5) Various pulp liquids
(A) Pulp and paper mill
(B) Flow management, proper replacement of pumps to reduce power costs.
(6) Coal / ore mixed water
(A) Mines
(B) Flow measurement during coal preparation / dressing
(7) Sugar solution, starch solution
(A) Sugar factory, starch factory
(B) Processes applicable to edible pipes
(8) Water for cooling water and air-conditioning equipment, warm water
(A) Construction, building construction, maintenance of buildings
(B) Flow management and efficiency check
(9) Various processing fluids
(A) Chemical, pharmaceutical, and pharmaceutical factories
(B) Flow measurement at high / low temperature and high pressure
(10) Debris mixed water
(A) Construction company
(B) Flow measurement when sand, rocks, etc., which are the main seabed, are transported on a pump
(11) Rivers, sea water, salt water
(A) Chemical, food, pharmaceutical, petrochemical, salt factories
(B) Flow rate measurement mainly for cooling water and treated brine
(12) Clear water
(A) Electronic equipment manufacturing plant, chemical plant, semiconductor plant
(B) Measurement of fresh water flow
(13) Working oil
(A) Ironmaking, construction machinery, manufacturing plants
(B) Inspection and management of engine oil for switching on and off of large unloading trucks, and inspection and management of power lubricants for construction machinery.
(14) Cutting oil
(A) Automotive and related industry work machinery plants
(B) Flow rate distribution, inspection and management of working machine cutting oil.

The measurement of ultrasonic Doppler flow meters is based on the Doppler effect in physics. According to the acoustic Doppler effect, when there is relative motion between the sound source and the observer, the frequency of the sound perceived by the observer will be different from the frequency emitted by the sound source. This frequency change due to relative motion is directly proportional to the relative speed of the two objects.

In the ultrasonic Doppler flow measurement method, the ultrasonic transmitter is a fixed sound source, and the solid particles that move with the fluid play the role of an "observer" that moves relative to the sound source. Of course, it merely sends the incident light to the solid. The ultrasonic waves on the particles are reflected back to the receiving data. The frequency difference between the transmitted sound wave and the received sound wave is the Doppler frequency shift of the sound wave due to the movement of solid particles in the fluid. Since this frequency difference is proportional to the fluid velocity, the velocity can be obtained by measuring the frequency difference. Then the flow rate of the fluid can be obtained.

流量测量的一个必要的条件是:被测流体介质应是含有一定数量能反射声波的固体粒子或气泡等的两相介质. Therefore, a necessary condition for Doppler ultrasonic flowmeter flow measurement is that the fluid medium to be measured should be a two-phase medium containing a certain number of solid particles or bubbles that can reflect sound waves. This working condition is actually one of its great advantages, that is, this flow measurement method is suitable for the measurement of two-phase flow, which is a difficult problem for other flow meters. Therefore, as a promising two-phase flow measurement method and flow meter, ultrasonic Doppler flow measurement method is being increasingly applied.