RU2097706C1 - Vortex flowmeter - Google Patents

Abstract

FIELD: conversion of flow of gas and liquid in large-diameter pipes to electric signal. SUBSTANCE: bluff body 12 of flowmeter is composed of trapezoidal 4 and rectangular 5 prisms interconnected by minor base of trapezoidal prism 4 and side of rectangular prism 5 and is confined in guide 3 mounted on support 2. It is oriented with major base of trapezoidal prism in opposition to flow. Support 2 has laminar profile in cross-section and is anchored with the aid of base I on wall of pipe-line. Rectangular prism 5 is manufactured in the form of laminate structure composed of alternating restoring 13, 15, 17, 19, 21 and piezoceramic 14, 16, 18, 20 plates rigidly interjoined. Outputs of piezoceramic plates 22, 23, 24, 25 are connected to input of electron processor 9 making calculation operations in agreement with expressions:

, where U is primary signal in input circuits of electron processor; U is reference signal; U_O-;

;

, where

...U_1.1...U_1.n are voltages from outputs of piezoceramic plates located on one side of neutral surface of rectangular prism for bending deformations; U_2.1...U_2.n are voltages from outputs of piezoceramic plates located on opposite side of neutral surface of rectangular prism for bending deformation; K_1.1...K_1.n; K_2.1...K_2.n are proportionality factors. Output signal of flowmeter is determined by expression N = n•F, where n″ is proportionality factor, F is frequency of switching over of signal U. EFFECT: enhanced reliability and accuracy of vortex flowmeter. 5 dwg

Description

 The invention relates to measuring equipment and can be used, for example, to convert into an electric signal the flow rate of gas and liquid in pipes of large diameter.

 Known vortex flowmeters using vortex-forming turbines as a generator of vortices, as well as poorly streamlined bodies [1] Sensors, as a rule, have a non-linear characteristic and a limited measurement range, and also have a significant braking coefficient due to the diametrical fixing of a poor-streamlined body in the pipe, which limits their use in pipes of large diameter.

 A prototype of the invention is a Vortex Bar plug-in flow meter from Nice Instrumetation for measuring flow in large-diameter pipes [2] The flowmeter consists of a cylindrical rod inserted through an opening into the pipeline. The vortex-forming module is made in the form of a rectangular section cut in the rod, above and below which there are through holes. Liquid flows around this module and flows through the holes, exciting alternating vortex oscillations in the vortex-forming element. The signals are recorded embedded in the vortex module, a piezoelectric sensitive element.

 The disadvantage of the prototype device is that since the sensor operates, as a rule, in a turbulent flow, pressure pulsations caused by turbulence will be superimposed on the periodic pressure fluctuations generated in the vortex wake behind the vortex-forming section. These pressure pulsations will be perceived by the sensitive element as a useful signal, which will lead to the appearance of an additional error in the flow measurement. With an inaccurate installation of the sensor and transverse pulsations of the velocity in the stream, it will leak at an angle to the plane of symmetry of the rod. This will lead to the appearance of an additional error due to the fact that the characteristic size of the rod in the direction of flow will vary and, consequently, the vortex frequency will change, which is inversely proportional to the characteristic size. Since sensitive elements are not protected from vibration overloads, an additional error from external vibrations will appear.

 The proposed invention solves the problem of improving the accuracy of measurement.

где U первичный сигнал в цепях электронного процессора;
U_o опорный сигнал;

U_E1 K_1.1U_1.1+.+K_1.n.U_1.n.
U_E2 K_2.1U_2.1+.+K_2.n.U_2.n.
U_1.1.U_1.n. сигналы с выхода пьезокерамических пластин, расположенных по одну сторону от нейтральной поверхности прямоугольной призмы для изгибных деформаций;
U_2.1..U_2.n. сигналы с выхода пьезокерамических пластин, расположенных с противоположной стороны нейтральной поверхности прямоугольной призмы для изгибных деформаций;
K_1.1..K_1.n., K_2.1..K_2.n. коэффициенты пропорциональности.The solution to this problem is achieved by the fact that in a vortex flowmeter containing a poorly flowed body mounted on a rack for fixing it in a pipe, and a piezoceramic sensing element that converts oscillations in the vortex wake of a poorly flowed body into an electrical signal, the poorly flowed body consists of a trapezoidal and rectangular prism, interconnected by a smaller base of a trapezoidal prism and a side face of a rectangular prism, enclosed in a guide and oriented by a large base of the trapezoid the ideal prism towards the flow, while the stand has a laminar profile in cross section, and the piezoceramic sensitive element is made in the form of a rectangular prism of a layered structure consisting of alternating elastic and piezoceramic plates rigidly interconnected, the outputs of the piezoceramic plates are connected to the input of the electronic processor, performing computational operations in accordance with the expressions:

where U is the primary signal in the circuits of the electronic processor;
U _o reference signal;

U _E1 K _1.1 U _1.1 +. + K _1.n. U _1.n.
U _E2 K _2.1 U _2.1 +. + K _2.n. U _2.n.
U _1.1 .U _1.n. signals from the output of piezoceramic plates located on one side of the neutral surface of a rectangular prism for bending deformations;
U _2.1. .U _2.n. signals from the output of piezoceramic plates located on the opposite side of the neutral surface of a rectangular prism for bending deformations;
K _1.1. .K _1.n. , K _2.1. .K _2.n. proportionality factors.

The output signal of the vortex flowmeter is determined by the expression:
N IF
where And the coefficient of proportionality;
F signal switching frequency.

 In FIG. 1 presents one of the options for constructive implementation of the vortex flowmeter; figure 2 view along arrow B in figure 1; figure 3 section aa in figure 2; figure 4 flow of the flow meter; figure 5 is a cross section of one embodiment of a technical implementation of a rectangular prism of a poorly streamlined body.

 In the drawing: 1 base, 2 uprights, 3 cylindrical guides, 4 trapezoidal prisms, 5 rectangular prisms, 6 pipelines, 7 and 8 - flow channels, 9 electronic processor, 10 average flow rate range, 11 flow velocity profile in the pipe, 12 poorly streamlined body, 13, 15, 17, 19 and 21 elastic plates, 14, 16, 18 and 20 piezoceramic plates, 22 25 electrical outlets of piezoceramic plates, 26 - deflection shape of a rectangular prism.

 The vortex flowmeter (figure 1) contains a poorly streamlined body 12, consisting of a trapezoidal 4 and rectangular 5 prisms. Rectangular prism 5 is made in the form of a layered structure and consists of elastic plates rigidly interconnected and piezoceramic plates. The outputs of the piezoceramic plates are connected to the input of the electronic processor 9.

 The poorly streamlined body (Fig. 1) is enclosed in a cylindrical guide 3 and mounted on a stand 2, cantileverly fixed with a base 1 on the wall of the pipe 6. Stand 2 has a laminar profile in cross section, for example, a Zhukovsky profile (section AA in FIG. 1).

 The trapezoidal 4 and rectangular 5 prisms are mounted across the guide 3 (Fig. 2) and divide the guide 3 into two channels 7 and 8. The axis of symmetry of the cylindrical guide 3 is located at a distance r from the pipeline wall and coincides with a diameter of 11 of the average flow velocity over the pipeline section ( speed profile 11).

 Rectangular prism (figure 4) includes elastic 13, 15, 17, 19 and 21 and piezoceramic plates 14, 16, 18 and 20, rigidly interconnected, the electrodes of piezoceramic plates have electrical outputs 22 25. Arrow 26 shows the shape of a possible deflection when bending strain. The axis OX coincides with the plane of the neutral surface of the prism under bending deformations.

 Vortex flowmeter operates as follows.

 When flowing around a poorly streamlined body (Fig. 1) by an incident flow on the faces of a trapezoidal prism 4 of a poorly streamlined body, the sign of the velocity profile periodically changes and the flow detaches from the faces of the trapezoidal prism 4 of a poorly streamlined body and a vortex flow forms. Moreover, in the channels 7 and 8 formed between the guide and the poorly streamlined body, two regions of vortex formation are formed, limited by the side walls of the poorly streamlined body and the inner surface of the guide 3. At the initial moment, due to the incomplete symmetry of the channels 7 and 8, the vortex on one of the faces of prism 4 is generated earlier than on the other. The resulting vortex is carried into the channel, for example, 7, and the stall of the vortex into another channel 8 is delayed until the vortex leaves the channel 7. Due to the guide 3 between the channels 7 and 8, pneumatic positive feedback is formed in the flow part of the sensor and the vortex formation process is stable periodic in nature. At the same time, a pressure differential arises on the lateral surfaces of the poorly streamlined body, pulsating with a frequency proportional to the local flow velocity in the region of the guide of the low-flow body. Under the action of a pulsating pressure drop, prism 4 performs bending vibrations.

 When bending prism 4 (figure 4), for example, in the direction of arrow 14, the piezoceramic plates 2 and 4 located above the neutral surface (axis OX) are stretched, and the plates 6 and 8 located below the neutral surface are compressed, while under the action of deformations at the electrodes of the piezoceramic plates located above the OX axis, an electric voltage of the same sign is created, and at the electrodes of the piezoceramic plates located below the OX axis, the opposite sign.

где U_E1 K_1.1U_1.1+.+K_1.n. U_1.n.;
U_E2 K_2.1U_2.1+.+K_2.n.U_2.n.;
U_1.1.U_1.n. напряжения с выходов пьезокерамических пластин, расположенных по одну сторону от нейтральной поверхности прямоугольной призмы для изгибных деформаций;
U_2.1.. U_2.n. напряжение с выходов пьезокерамических пластин, расположенных с противоположной стороны нейтральной поверхности прямоугольной призмы для изгибных деформаций;
K_1.1..K_1.n., K_2.1..K_2.n. коэффициенты пропорциональности.The voltages are fed to the input of the electronic processor 9, where they are subtracted in accordance with the dependence of the form:

where U _E1 K _1.1 U _1.1 +. + K _1.n. U _1.n. ;
U _E2 K _2.1 U _2.1 +. + K _2.n. U _2.n. ;
U _1.1 .U _1.n. stresses from the outputs of piezoceramic plates located on one side of the neutral surface of a rectangular prism for bending deformations;
U _2.1. . U _2.n. voltage from the outputs of piezoelectric ceramic plates located on the opposite side of the neutral surface of a rectangular prism for bending deformations;
K _1.1. .K _1.n. , K _2.1. .K _2.n. proportionality factors.

Since the signs of the electrical voltages from the outputs of the piezoceramic plates are different, after performing the operations in accordance with expression (2), a voltage pulse U _E will be generated, the amplitude and shape of which is proportional to the amplitude and shape of the pressure drop pulsation on a rectangular prism. When the pressure drop of the opposite sign appears on the prism, in accordance with expression (2), the next voltage pulse U _E will be generated.

где U первичный сигнал в цепях электронного процессора 9;
U_o опорный сигнал.After comparing the signal proportional to U _E with a given level of U _o in accordance with the dependence of the form:

where U is the primary signal in the circuits of the electronic processor 9;
U _o reference signal.

 In this case, the switching frequency of the signal U will be proportional to the frequency of the pulsating differential pressure on the rectangular prism 5 and, therefore, the local flow velocity in the region of the guide 3 of the streamlined body 12.

A poorly streamlined body can be located at point 10 of the profile 11 of the flow rate in the pipe, where the local flow rate is equal to the average flow velocity over the cross section of the pipeline 6. Since the flow rate of gas flowing through the pipeline 6 is equal to the product of the average velocity over the cross section of the pipe 6 by the cross-sectional area, then the output signal of the flow meter will be proportional to the gas flow in the pipeline 6 and is determined by the expression:
N IF
where And the coefficient of proportionality;
F signal switching frequency.

 The proportionality coefficient And is determined by the design parameters of the pipeline 6 and the physical properties of the working medium in the pipeline 6.

 The turbulence of the flow does not affect the accuracy of the sensor, since the vortex spatial velocity pulsations do not interact directly with the poorly streamlined body, which is protected by a cylindrical guide.

 The transverse component of the velocity of the turbulent flow, which is the source of the error, creates a pressure pulsation at the inlet and outlet of the cylindrical guide at the same time. We can assume (given the small size of the sensor and the value of the speed of sound) that the pressure pulsation due to the transverse component of the flow velocity simultaneously affects the rectangular prism 5 (Fig. 1) from all sides. In this case, the piezoceramic plates located both above and below the neutral surface OX (Fig. 5) are tested, depending on the sign of the external pressure, either comprehensive compression or all-round tension. In this case, the electric voltage from the output of the piezoceramic plates above and below the neutral surface will have the same sign and when performing mathematical operations by the electronic processor in accordance with expression (2), the resulting signal will be zero.

Pressure pulsations that could occur behind the column in the immediate vicinity of the poorly streamlined body also do not affect the measurement accuracy, since, firstly, the poorly streamlined body is protected by a cylindrical guide, and secondly, the column has a laminar profile in cross section, and its geometry is selected in such a way that in the range of numbers R _e at which the flowmeter works, there is a laminar flow around the rack.

 External mechanical vibrations do not impair the accuracy of measurements, since they propagate through the sensor structural elements and are perceived by piezoceramic plates of a rectangular prism due to longitudinal and transverse deformations of a rectangular prism, while the voltage at the output of the piezoceramic plates has the same sign. After processing the signals from the output of the piezoceramic plates in accordance with expression (2), the resulting signal will be zero.

 The electronic unit is implemented using a modern elemental base of the series: 140, 564, 1113 and 1718, and the sensitive element is made using piezoelectric ceramics of the TsTS-19 type.

 Thus, this technical solution makes it possible to measure the gas flow velocity with high accuracy, regardless of external disturbances caused by turbulence of the flow and mechanical vibrations.

Claims (1)

A vortex flowmeter containing a poorly streamlined body mounted on a stand for fixing it in a pipe, with a piezoceramic sensing element that converts the oscillations in the vortex wake of a poorly streamlined body into an electrical signal, characterized in that the poorly streamlined body is made of trapezoidal and rectangular prisms connected between each other with the smaller base of the trapezoidal prism and the side face of the rectangular prism, placed in the guide and oriented by the large base of the trapezoidal prism flow, while the stand in the cross section has a laminar profile, the piezoceramic sensitive element is made in the form of a layered rectangular prism consisting of alternating elastic and piezoceramic plates rigidly interconnected, and the outputs of the piezoceramic plates are connected to the input of the electronic processor introduced into the flowmeter performing computational operations in accordance with the expressions

where U is the primary signal in the circuits of the electronic processor;
U _o reference signal;

U _{E 1} K _{1 . 1 .} U _{1 . 1 .} + + K _{1 . n} U _{1 . n.} ;
U _{E 2} K _{2 . 1 .} ; U _{2 . 1 .} + + K _{2 n} U _{2 n .} ,
U _{1 . 1 .} U _{1 . n.} - stresses from the outputs of piezoceramic plates located on one side of the neutral surface of a rectangular prism for bending deformations;
U _{2 . 1 .} U _{2 . n.} - stresses from the outputs of piezoceramic plates located on the opposite side of the neutral surface of a rectangular prism for bending deformations;
K _{1 . 1 .} K _{1 . n} , k _{2 . 1 .} K _{2 . n.} are the proportionality coefficients, and
N IF,
where And the coefficient of proportionality;
F signal switching frequency;
N signal at the output of the vortex flowmeter.

Images