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flow meter characteristics and applications
Measurement of fluid flow of the instrument referred to as flow meters or flow meters. Flow meter is an important instrument of industrial measurement one. With the development of industrial production, on the flow measurement accuracy and range of increasingly demanding, ever-changing flow measurement technology. In order to adapt to various uses, all types of flow meters one after another. Currently in use has more than 100 kinds of flowmeter. From a different point of view, flow meters have different classifications. There are two methods commonly used classification, one flow meter with the measuring principle by summing Category: Second, the structure according to principles of classification of flow meters.
1, according tomeasurementprinciplecategories
(1) mechanics: the principle of instruments belonging to such a differential pressure using Bernoulli theorem, rotor; using the impulse momentum theorem type, movable tube; using Newton's second law of direct mass type; use of fluid Momentum principle target type; use of angular momentum theorem turbine; use of fluid oscillation theory of vortex-type, vortex type; use of total static pressure difference of the Pitot tube and the displacement and the weir, trough, etc..
(2) Electrical Principles: forofsuchinstruments are electromagnetic theory,differentialcapacitive,inductive, resistive strain so.
(3) acoustics: acoustic principle ofultrasonic flow measurement has. Acoustic-type (wavetype), etc..
(4) ThermalPrinciples:Principles ofmeasurement of thermal heat-type flows area directcalorimetric,type, and so indirect calorimetry.
(5) optics: Laser type, photoelectrictype, and so are the instruments of such principles.
(6) The principle ofphysics:nuclearmagnetic resonance type, nuclear radiation type, andso aretheinstruments of such principles.
(7)OtherPrinciples:Principles marked (tracer principle, nuclearmagneticresonancetheory), and other related principles.
Second, thestructureaccordingto principles of classification of flowmeters
According to the actual currentflowmeterproducts, according to flowmeter principle canbebroadlyclassified into the following types:
1. Volumetric flowmeter
Flow meter is equivalent toastandardvolume of container, which after another to be measuredonthe flowof media. Gas flow rate and measure the numberofthemore higher the frequency of the output.The principle of positive displacementflow meter is simple, suitable for measuring high viscosity, lowReynolds number flow. According to rotation of the shape, the current sub-products: suitable for measuring liquid flow meter Oval gear, Roots Flowmeter (Roots flow meter), rotary piston and scraper-type flow meter; suitable for measuring gas flow servo volumetric flow meter, film and rotating simple flowmeter.
2.Impeller-type flowmeter
The workingprinciple of impeller flowmeter is placed in the measured fluid inthe impeller, by the impact of the rotating fluid flow to theimpeller rotation speed to reflect the size of traffic.Impeller flow meter is a typical water meter and turbine flow meters, and its structure can be mechanical or electrical drive pulse output output-type type. General mechanical drive output low accuracy of water meters, the error is about ± 2%, but the simple, low cost, domestic volume production and standardization, generalization, and serialization. Electrical pulse signals output high accuracy turbine flow meter, the general error of ± 0.2% 1 0.5%.
3.Differential pressure flow meter (variablepressure drop flow meter)
flow meter from the first deviceandseconddevice component. Flow measurement devices, said first device, install it in the measured fluid pipeline, production and flow (velocity) is proportional to the pressure difference for the secondary display device flow. Said second device displayed instrument. It receives the differential pressure measuring device produces signals, and converts it to display the corresponding flow. Differential pressure flow meter in a device often cutting device or dynamic pressure measurement device (pitot tube, all-speed control, etc.). Secondary devices for a variety of mechanical, electronic, modular differential pressure flow meter display instrument accompanied. Differential pressure differential pressure sensor of dollars more for the elastic element. As the relationship between differential pressure and flow rate were the square root, it flows show open square meters are equipped with devices to enable the flow of linear scale. Most instruments also have flow totalizer device to display the cumulative flow for economic accounting. This differential pressure flow measurement method using a long history of relatively mature, generally used around the world more important occasion, about a variety of flow measurement of 70%. Power plant main steam, feed water, condensate water flow measurement using this meter are.
4.Variable area flow meter (such as pressuredrop flow meter)
On the large conical flow underthesmallfloat in the fluid by the bottom-up flow of theforceandmovement. When this force and floatthe"DisplayWeight" (minus the weight of the float itself,whichsuffered thebuoyancy fluid) equilibrium when the childisstillprisoners. Static float heightcan be used as a measure of flow rate. As the flow meter flow path cross-sectional area varies with the height of the float, and float stable fixed upper and lower part of the pressure difference when the same, so the variable area flow meter, said flow meter or other voltage drop flowmeter. The flowmeter is a typical meter rotor (float) flow meter.
5.Momentum Flowmeter
Measurement of fluid used to reflect theflow of momentum, said the size of the momentum flow meter flowmeter. As the flow of fluid momentum P and thefluid density and velocity v proportional to the square, that is, pv2, when the flow passage cross section to determine when, v andthe volume flow rate Q is proportional to, so p Q2.Proportional coefficient set A, then Q = A Therefore, the measured P, can reflect the flow Q. This type of flow meter, most of the momentum transfer component used for the detection of pressure, displacement or force, etc., and then measuring flow. This flow meter is a typical instrument type and the rotational wing target plate flow meter.
6.Impulse flowmeter
Flow measurement using impulsetheoryofflow meter, said impulse flow meter, are used formeasuringtheflow of granular solid medium, also used to measure themud,andabrasives such as liquid crystal flow.Flow measurementrange from a few kilograms per hour to nearly 10,000 tons.A typical instrument is the horizontal component type impulse flow meter, its measuring principle is that when measured medium free-fall from a height h to detect a tilt angle of the board to generate a momentum, momentum of the horizontal component mass flow rate proportional to the horse, so measuring the horizontal component can be reflected in the size of the mass flow rate. By signal (9) of the detection method, the displacement detection type flow meter sub-type and direct force measurement type.
7.Electromagnetic Flowmeter
Application of electromagnetic flowmeterisa moving conductor in a magnetic field theinducedelectromotiveforce, while the induced voltage isproportional tothe size of itand flow through the pipeline flowmeasuringelectromotive force toreflect the principles whichmade.The measurementaccuracyandsensitivity are high. Industry to measure more thanwater,theflow of pulp and other media. Maximum diametercanbe measured up to 2m, and minimal pressureloss.However, the low conductive medium, suchas gas, steam, etc. can not be applied.
Higher cost ofelectromagneticflowmeter,and the signal vulnerable to externalmagneticinterference,affecting the flow measurement in industrialpipewideapplication. To this end, the continuousimprovementofproduct updates, to computer development.
8.Ultrasonic Flowmeter
Ultrasonic flowmeter is based on theultrasonic transmission medium in the flow rate is equal to theaverage velocity measured medium and the speed of sound itself andthe principles of geometry designed. It is also to reflect the flow velocity from the measured size. Ultrasonic Flowmeter Although only appeared in the 70's, but because it can be made non-contact type, and can be linked with the ultrasonic water level measurement for open flow of fluid without producing disturbance and resistance, so it is popular, is a very promising flow meter.
Made use of the Doppler effect Dopplerflow meter wide attention in recent years, are considerednon-contact measurement of the ideal two-phase flowmeter.
9.Oscillatory fluid flow meter
Oscillatory fluid flow meter is the use offluid flow conditions in a particular flow will oscillate, and theoscillation frequency and velocity is proportional to theprinciples of design. When the flow passage cross section isconstant, velocity and volume flow rate proportional to theconductivity. Therefore, themeasurement of the oscillation frequency can be measuredflows. This flow meter is 70 years developing anddeveloped. Both because of its non-rotating parts,and the advantages of digital output pulse, is verypromising. The typical products are vortex flowmeter,Swirlmeter.
10. Mass Flow Meter
As the volume of fluidtemperature,pressureand other parameters, volume of traffic thatflows withthe size ofthe parameters required to givemedia.In the medium parameterschangingcircumstances, it is often difficult to achieve thisrequirement,resulting in distortion meter display value.Therefore, the mass flow meterto be widely used and valued. Direct mass flow meter and indirect sub-two. Direct mass flowmeter and mass flow using the principle of direct measurement, there are currently used thermal capacity, angular momentum-type vibration gyro-style, Magnus-effect and the Coriolis force mass flowmeter type and so on. Indirect mass flowmeter is the density and volume flow meter directly obtained by multiplying the mass flow rate.
In modern industrial production, the temperature of working fluid flow and pressure operating parameters continue to increase, in the case of high temperature and pressure, due to material and structural and other reasons, the application of direct mass flowmeter difficulties, and indirect quality As the density meter by meter humidity and pressure limit the scope of application is often not a good practice. Thus, widely used in industrial production is temperature and pressure compensated mass flow meter. May see it as an indirect mass flowmeter is not equipped with density meters, but the use of temperature, pressure and density of a, with temperature, pressure signal by the function calculation for the density of the signal, and the volume flow by multiplying the mass flow. The current temperature and pressure compensation mass flowmeter Although practical, but significant parameter ranges tested medium, or very quickly, the right to compensation will be very difficult or impossible, so further research in the actual production for the mass flux meter and density meter, or a topic.
Chen common structural principle of the flowmeter the various structures of the flow meter than many, if applied to a variety of open channel flow measurement weir flow meter, slotted flow meter; suitable for measuring flow in large diameter plug-flow meter; measurement layer Laminar Flow Flow meter; suitable for two-phase flow meter measuring the relevant law; and the laser method, NMR flowmeter and multiple tracer dilution method in flow measurement and so on. With the development and practical application of technology needs, the new flow meter type flow meter will emerge will be more complete.