Hot:13322013-10-27 17:54:49 From: FTD Automation Instruments
General Introduction of Turbine Flowmeter
One. Turbine Flowmeter Overview
Turbine flow meter is the main product of flow (velocity) meter in turbine type.Flow meter in turbine type also includes wind velocity meter and water meter.TURBINE FLOWMETER is composed of sensor and converting display instrument. Sensor uses multi-turbine rotor to sense the average velocity of flow to calculate the flow or cumulative flow. The rotating speed(or Revolutions Per Minute) can be detected by mechanical ,magnetic or photoelectric method and displayed, transmitted and recorded by read out device.It was said that America declared first Turbine flowmeter patent in 1886.The Turbine flowmeter patent in 1914 told that flow has some relationship with frequency. The first America TURBINE FLOWMETER was invented and made in 1938 and it was used to measure the fuel on airplane.This kind of flow meter was applied well until the end of World WarⅡ because of the need of flow meter with high accuracy and rapid response in jet engine and liquid jet fuel. At present ,it has been applied in many departments in petroleum,chemical industry,research,national defense and measurement.
Turbine flowmeter,volume flow meter and Coriolis mass flow meter are best three kinds of flow meter with high repeatability and gigh accuracy.TURBINE FLOWMETER has its own traits ,such as simple structure,fewer processed components, low weight ,convenient maintenance,large flow capacity and adapting high parameters. All these traits can hardly be reached by the other two kinds of flow meter.Turbine flowmeter ,as the flow meter in common use,has developed with various kinds,full series,many specifications and the scale of mass production. It should be noted that,besides wide application in industry,Turbine flowmeter has also be widely applied in some special departments ,such as research experiment ,national defense and measure,playing its role fully.In these fields,they have special structure design for the requirements from measured medium and they are special instruments without mass production.
Turbine flowmeter was widely applied in the following measured medium:petroleum,organic liquid,inorganic liquid,liquefied petroleum gas ,nature gas,coal gas and flow in low temperature, etc.Transport station and gathering station of liquefied petroleum gas,refined oil,light crude oil and first and end station of large transporting crude oil pipe line use Turbine flowmeter to do trade settlement .TURBINE FLOWMETER is dedicated for nature gas in Europe and America.Netherland has used 2600 sets gas Turbine flowmeter,various sizes with pressure from 0.8MPa to 6.5MPa ,on mature gas pipelines .Turbine flowmeter has become nature gas flow meter.
Two .Turbine Flowmeter Working principle
when measured medium passed through the sensor,turbine will rotate at the propelling power of flow .Its rotating velocity is proportional to average flow .Rotation of the turbine changes the magnetic resistance of magneto-electronic converter in period .Then ,the flux of detection coil changes cyclically and produces cyclical induced electromotive force which is pulse electric signal .After amplified ,it is transmitted to display.
Flow equation of the flow meter can be divided into two parts:practical flow equation and theoretical flow equation.
Characteristics are related to structure size of the sensor and viscosity of the fluid. In the non-linear paragraph,characteristics are mainly affected by bearing friction and viscous resistance of the fluid.When flow is under minimum flow of the sensor,instrument coefficient varies with the flow rapidly.The relationship between pressure loss and flow is almost square. When flow is over the maximum flow of the sensor ,pay attention and prevent the hole effect.The shape of characteristic curve is similar between those TURBINE FLOWMETER with similar structure.The only difference is system errors.
Instrument coefficient of the sensor is checked by check device and it is totally different from principle of inner flow. Sensor is treated as a black box and converting coefficient is determined according to input (flow ) and output (frequency pulse signal).It is convenient to practical use.Please pay attention that the converting coefficient is conditional :the checking condition is referred condition.If there is the from the condition when used,the coefficient will vary.The varying condition is depended on the type of the sensor ,installation condition of the pipe and parameters of the fluid.
Scholars all over the world have provided many theoretical flow equations ,they are suitable to various sensor structures and working conditions of flow .Until now. Hydrodynamic characteristics of flow meter are still unclear and there are complex relationship between fluid and flow characteristics. When there are whirlpools and non-symmetric velocity distribution, hydrodynamic characteristics will be very complex. Instrument coefficient can not be derived from theoretical equation and it should be determined by practical calibration .However, there are great practical meanings of theoretical equation. It can be used to guide the design of structure parameters and prediction and calculation of instrument coefficient changing rules when operating condition varied in the working site.
(1) Practical flow equation
qv =f/k qM = qvρ
Here ：qv volume flow ,m³/s;
qM is mass flow ,Kg/s;
f the frequency of the output signal of flow meter
K instrument coefficient of flow meter,P/m³
The relationship between coefficient and flow (Pipe Reynolds number) is showed in Figure 2.Instrument coefficient can be divided into two paragraphs:linear paragraph and (??)-linear paragraph.Linear paragraph is about 2/3 of the working paragraph
(2) Theoretical flow equation
(3) According to Moment of momentum Theorem ,get turbine movement equation:
j:inertia moment of turbine
dw/dt:rotation acceleration of turbine
M1:propelling moment of fluid
M2:viscous resistance moment
M3:fabrication moment of bearing
M4: magnetic resisitance moment
When turbine rotares with a constant velocity,j× =0
M1=M2+M3+M4,According to theoretical analysis and experiment ,
n: rotary speed
qv : mass flow
A: coefficient related with fluid character(density and viscosity,etc)and structure parameters of turbine (blade angle,turbine diameter,cross-sectional area of flow pipe,etc)
B:coefficient related to the seam between blade and inner pipe wall and flow velocity distribution.
C:coefficient related fabrication moment
Click to Turbine Flowmeter
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