RU2161779C1 - Flowmeter - Google Patents

Abstract

FIELD: instrument engineering. SUBSTANCE: flowmeter is designed to measure flow rate in large-diameter pipelines (more than 200 mm). Flowmeter includes two waveguide resonators positioned in different sections along pipeline from its external side. Each resonator is made sectional. It contains K three-arm circulators and waveguides with elastic end walls (membranes) common with pipeline. Differential pressure coupled functionally with flow rate is determined by difference of inherent frequencies of resonators. EFFECT: higher sensitivity. 5 dwg

Description

 The invention relates to the field of measuring technology and can be used to measure the flow of substances transported through the pipeline, and is applicable in the food, chemical, oil and other industries, in the energy sector, etc. In all these industries, the preferred field of application is flow measurement in pipes large diameter (over 200 mm).

 Known flow meters based on different physical principles (Kremlin P. P. Flow meters and quantity counters. L .: Mechanical engineering (Leningrad branch), 1975). In particular, the flow meters described in this book (chapters I-V) are known, based on the measurement of the differential pressure in the pipelines and associated with the use of narrowing nozzle devices of various shapes and designs located inside pipelines. The use of such flowmeters causes a violation of the flow structure, the development of turbulence, a violation of the all-metal construction of the pipeline during pressure selection. In many practical tasks this is unacceptable. For example, when measuring flow rates in severe operating conditions (at chemistry, energy, etc.), it is necessary to use instruments that do not have these drawbacks. At the same time, the devices used should be simple and reliable in operation, during repair and routine maintenance, be interchangeable.

 Closest to the technical nature of the proposed device is a flow meter adopted as a prototype (Billeter T.R., Phillipp L.D., Schemmel R. R. Microwave fluid flow monitor. US Pat. N 3939406, NKI 324-58.5). This flow meter is non-contact, not violating the structure and dynamics of the flow. It contains two volume microwave resonators, which are installed outside the pipeline in different sections along its length. Each of these resonators has a common elastic end wall (membrane, diaphragm, etc.) with the pipeline, as well as blocks connected to each resonator for generating the resonant (natural) frequency of the electromagnetic oscillations of the resonator and a unit for comparing the resonant frequencies of these resonators. The output signal of the comparison unit corresponds to the measured flow. Such a device ensures the preservation of the all-metal construction of the pipeline and does not contain any structural elements inside it. This does not violate the hydrodynamic characteristics and flow structure. The resonant frequency of each volume resonator is a function of the pressure inside the pipeline in that section in the region of which the resonator is installed. This frequency is usually of the order of several gigahertz and depends on the size of the resonator, the selected "working" type of electromagnetic waves. In this case, a change in pressure in the pipeline leads to a displacement of the flexible wall common to the resonator (this is its end wall) and the pipeline, changing the longitudinal size of the cavity of the resonator and, as a consequence, its resonant frequency. In the pipeline, the pressure has a different value in its different sections. The values of the deflection of the end walls of the resonators corresponding to these pressure values, located along the pipeline in its two sections, are also different. The pressure drop depends functionally on the flow rate of the substance in the pipeline. By determining this pressure drop from the difference in resonant frequencies of the two resonators, one can find the flow rate and the flow rate of the substance. In such a flow meter, the sensitivity depends, among other factors not related to the device, also on the distance between the resonators installed on the pipeline along its length.

 An increase in the sensitivity of the flowmeter can be achieved by increasing this distance between the resonators, which is often not possible. So, for example, in the prototype device for determining the velocity of liquid sodium in the pipeline equal to ~ 1.8 m / s (minimum value) from the pressure drop, the distance between the resonators should be ~ 3 m. With a shorter distance, the sensitivity of the flowmeter is unacceptably low.

 The aim of the invention is to increase the sensitivity of the device to the measured flow.

 The goal in the proposed flow meter, which contains two waveguide resonators located along the pipeline on its outer side, each of which has an elastic end wall in common with the pipeline, is achieved by the fact that it is equipped with three-arm circulators and waveguides with elastic end walls in each cavity K in the number of circulators , the resonators are made composite, and each circulator mates adjacent sections of the resonators with two of its arms, and is connected to the corresponding waveguide by a third arm, which has a common with the pipe elastic end wall.

 Significant differences, according to the authors, is the implementation of each resonator composite, having K three-arm circulator, and each of them matches two adjacent sections of the resonator with two of its shoulders; the third arm of the circulator is connected to the corresponding waveguide having a common elastic end wall with the pipeline.

 The set of distinctive features of the proposed device determines a new property of the proposed flow meter: it is possible to perceive the useful signal simultaneously by the elastic end walls K of the waveguides included in each of the composite resonators located in different sections along the pipeline from the outside. This property provides a useful effect formulated for the purpose of the proposal.

 The invention is illustrated by drawings. Figure 1 shows a schematic diagram of the formation of a standing wave in a waveguide resonator with repeated perception of pressure in the pipeline of one of the counterpropagating waves in the resonator, forming a standing wave. Figure 2 shows a diagram when, to obtain useful information, not one, but both counterpropagating waves in the resonator are used, which perceive pressure in the pipeline due to the deflection of the elastic end walls separately. Figure 3 shows a diagram of a device corresponding to the sensing scheme in figure 1. In FIG. 4 is a sounding diagram of FIG. 2. Figure 5 is a functional diagram of a flow meter.

 In the drawings of the device (Fig. 3), (Fig. 4) and (Fig. 5), the following notation is introduced. Here 1 is a pipeline with a controlled substance; 2 and 3 - waveguide resonators; 4 - three-arm circulators; 5 - waveguides with elastic end walls 6; 7 and 8 - blocks for the generation of electromagnetic waves and registration of resonant frequencies; 9 - block comparing resonant frequencies; 10 - indicator.

 The device operates as follows. This device provides multiple and simultaneous perception of the pressure value (by measuring the magnitude of the deflection of the elastic element) in each of the two sections of the pipeline. In this case, accordingly, the sensitivity to the measured value increases manifold, i.e. to the deflection of the membrane caused by the current pressure value in each of the sections of the pipeline. The informative parameter of the flow sensor in this device is the resonant frequency f (x) of electromagnetic oscillations of the composite waveguide resonator, where x is the deflection of the membrane, or rather its central part relative to its initial position, corresponding to the absence of movement of the substance flow.

 Compared with the prototype, where each waveguide resonator has only one elastic end wall in common with the pipeline, in the proposed device, each such resonator, which is now composite, has K = 2, 3, ... elastic end walls (membranes) common with the pipeline and located in the same cross section.

где ρ - плотность вещества, ν - вязкость, D - диаметр трубопровода, μ - коэффициент трения, g - ускорение свободного падения.As described in the description of the prototype device, the pressure drop ΔP in the area of length l between the two regions of the arrangement of the resonators is expressed by the following formula:

where ρ is the density of the substance, ν is the viscosity, D is the diameter of the pipeline, μ is the friction coefficient, g is the acceleration of gravity.

 A change in the flow rate and flow rate of the substance leads to corresponding changes in the value of the coefficient of friction, which also depends on the degree of roughness of the walls of the pipeline. The elastic wall can be made, for example, of stainless steel. The thickness of the diaphragm can be 0.1 - 0.2 mm, and the diameter of ~ 10-40 mm (depending on the diameter of the pipeline).

Obviously, the presence of several thin membranes in the same section of the pipeline can reduce its strength in such a measuring section. Therefore, the preferred field of application of the proposed flow meter containing in each of the resonators several of these membranes is flow measurement in pipelines of relatively large diameter (more than 200 mm). For them, the presence of several membranes in each of the two sections does not reduce the strength and reliability of the pipeline
In FIG. Figure 1 shows a schematic diagram of the formation of a standing wave in a waveguide resonator with the formation of a standing wave in this resonator with repeated perception of the value x of one of the counterpropagating waves in the resonator forming a standing wave. Figure 2 shows a conventional scheme using not one, but both counterpropagating waves to perceive the deflection of the elastic end walls (membranes) separately. The operation of sensing the membrane with electromagnetic waves in the cavity in these circuits is carried out as many times as necessary to obtain the required sensitivity. For the circuits of FIG. 1 and FIG. 2, the resonance condition in such synthesized resonators can be written in the linear approximation as follows:
2β _n L + K2β _n x = 2πn, (2)
where L is the total length of the waveguide path outside the sensing region, i.e. above the dashed line in figure 1 and figure 2; β _n = 2πf _n / V _f - phase constant; V _f - phase wave velocity in the resonator; f is the intrinsic (resonant) frequency of the electromagnetic waves of the nth resonator; K = 1, 2, ... is the number of soundings, i.e. the number of times that the waves forming a standing wave in the resonator interact with the elastic end element (membrane).

Число n соответствует номеру возбуждаемого типа колебаний.From relation (1) it follows

The number n corresponds to the number of the excited type of oscillation.

где x<<L.The sensitivity S _n = df _n / dx to the measured position of the membrane, characterized by the displacement x, as follows from expression (2), is

where x << L.

 Compared with the known flow metering device (prototype), the sensitivity to the position of the membrane and, accordingly, to the measured flow rate increases K times, since a change in the x position of the membrane in the proposed device leads to a K-fold change in the natural (resonant) frequency of the composite resonator .

 In FIG. Figure 3 and Figure 4 show variants of the device diagram corresponding to the conditional schemes discussed in figure 1 and figure 2 above. Here, on the pipeline 1, in two its sections along the length, two proposed composite waveguide resonators 2 and 3 are installed. In each of these resonators 2 and 3, interaction is made in each of the waveguides 5 with the elastic end element 6 of one (Fig. 3) or both (Fig. .4) counterpropagating waves separately. To ensure such separate interaction of the waves, three-arm circulators 4 are introduced into the composition of each of the resonators 2 and 3. The circulators 4 are connected to the waveguides 5 by their first and second shoulders. The places where these circulators are included in the gap of the waveguide resonator 2 and 3 can be arbitrary, i.e. both equidistant and with different intervals between adjacent circulators. The number of waveguides 5 with end elastic elements 6 and circulators 4 is selected taking into account the required sensitivity to the measured flow. It corresponds to the number of soundings, for which a waveguide 5 is connected to the third arm of each circulator 4, the other end of which has an elastic element (membrane) 6, common with the pipe wall 1. All elements 6 in each of the two resonators 2 and 3 are located in the same cross section of the pipeline 1.

 The sensors in the devices of FIG. 3 and FIG. 4 correspond to the circuits of FIG. 1 and FIG. 2. As can be seen from the diagrams in figure 3 and figure 4, they differ from each other by the inclusion of circulators; in these diagrams, the directions of the passage of waves through the circulators are indicated by arrows showing the wave path from one arm of the circulator to the other.

 The structure of the device, in addition to the resonators 2 and 3, also includes blocks 7 and 8 (figure 5). With their help, in resonators 2 and 3, respectively, electromagnetic waves are excited at frequencies corresponding to the resonant (natural) frequencies of these resonators. In the same blocks, the resonance frequencies of the resonators 2 and 3 are determined. Next, in the resonance frequency comparison unit 9, the measured frequencies are converted to values corresponding to the pressure inside the pipe 1 in the region of the first and second resonators, and the pressure drop is functionally related to the flow rate of the substance . The current value of the measured flow rate is determined by the readings of the indicator 10 connected to the output of block 9.

 Thus, in the proposed flowmeter due to the organization of multiple and simultaneous sensing of a set of elastic end elements in each of the synthesized composite waveguide resonators, the goal is achieved - a multiple increase in sensitivity. Such a flow meter can have wide practical application for measuring the flow rate of various substances transported through pipelines, without introducing any elements into the pipeline.

Claims (1)

 A flowmeter containing two waveguide resonators located in different sections along the pipe on the outside of the pipe, each of which has an elastic end wall in common with the pipeline, characterized in that it is equipped with three-arm circulators and waveguides with elastic end walls in each resonator K, according to the number of circulators, the resonators are made composite, and each circulator mates adjacent sections of the resonator with two of its arms, and is connected to the corresponding waveguide by a third arm, which has a common elastic end wall.

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