One, this article introduction ultrasonic flowmeter
with non-contact measurement, high measuring accuracy, stable operation and no pressure loss, and many other advantages, the current Ni has been widely used in the field of industrial testing, market demand for related products is very high.
With in the 80 s, the rapid development of electronic technology and sensor technology, studies on the basis of ultrasonic flowmeter are also continuously thorough, the related all kinds of involved people life and production of new products is also changing, appear constantly.
At present mainly concentrated on the study of ultrasonic flowmeter measurement precision in three aspects: including signal factors, factors of the hardware and the flow field in the three points.
Due to the ultrasonic flowmeter flow field status is very sensitive, the scene of the actual installation flow instability will directly affect the accuracy of measurement of flow meter
For ultrasonic flowmeter flow field is studied using the computational fluid dynamics (
Method, many scholars at home and abroad for ultrasonic flowmeter in the case of bend flow field numerical simulation, and experimental verification.
Previous studies mainly for avoid effect of installation.
But in some small and medium caliber ultrasonic flowmeter applications, due to the limitation of space, lack of buffer downstream of the bend pipe, fluid after flowing through the bend is not fully development, the detection precision is bend downstream radial secondary flow velocity greatly affected, need to evaluate installation effect, and the corresponding compensation method.
This research adopts CFD simulation analysis 90 & deg;
Single bend downstream formation reason, the secondary flow error and the error of calculation formula for quantitatively analyzing different buffer downstream of the bend pipe, the secondary flow under different Reynolds number error influence on measurement accuracy, eventually get error correction.
By simulation, bend the top and at the exit at the bottom of the pressure difference associated with bend strength of secondary flow, put forward in the actual measurement can be obtained by the pressure difference to the secondary flow error correction method.
The study can be used for the analysis of error analysis of other type of ultrasonic flowmeter, the design and installation of ultrasonic flowmeter is of great significance.
Second, the measurement principle and error form 1.
1 ultrasonic flowmeter measurement principle for this study, a double probe method of time difference ultrasonic flowmeter.
Time difference method is to use the acoustic pulse wave in fluid in forward and reverse transmission time to measure the fluid velocity.
Double probe ultrasonic flowmeter principle diagram is shown in figure 1.
Forward and backward propagation time for t1 and t2, track line with an Angle pipe wall & theta;
, cross-sectional area of the pipeline is S, track online line of average flow velocity expression of vl and volume flow rate Q: type: L & ndash;
The distance between the two probe ultrasonic flowmeter;
Pipe surface average flow velocity, flow rate correction coefficient K will track line speed vl correction for the average speed of the vm of flow in the cross section.
2 secondary flow error formation fluid flows through the pipe, tube fluid interaction by centrifugal force and viscous force, radial section is formed on a pair of reverse symmetric vortex in pipe as shown in figure 2, called bend secondary flow.
Have nothing dimension number, number of dean Dn available to represent the bend strength of secondary flow.
When the pipe model is fixed, dean number Dn only related to the Reynolds number Re.
The study found that the flow velocity, the greater the intensity of the secondary flow, the greater the secondary flow gradually along with the development of the flow.
Type: d & ndash;
The pipe diameter, R & ndash;
Bend radius of curvature.
Bend downstream of the flow of the secondary flow in the radial plane, the bend of the secondary flow vertical and horizontal errors.
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