RU2068543C1 - Method of measurement of mass flow rate of liquid and gaseous media - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: acoustic cylindrical wave is radiated into flow, reflected wave is registered and its frequency is measured. By this frequency density of medium is determined. Normal wave on frequency corresponding to one of critical components of series ω_cr=a^-1x, where a is acoustic radius of pipe-line, C is sound velocity, is emitted into flow in addition. Frequency is changed up to achievement of new value of critical frequency and difference between values of frequencies is measured and used to find value of volumetric flow rate. Value of mass flow rate is determined as product of volumetric flow rate by density. EFFECT: improved authenticity of method. 1 dwg

Description

 The invention relates to measuring technique and can be used to determine the mass flow rate of liquid and gaseous media.

 A known method of determining the velocity of a medium by Doppler shift in the frequency of the probe radiation in acoustics [1] The main disadvantages of the Doppler methods: the need for the presence in the measured stream of scattering, probe radiation radiation; a large error in measuring the velocity (flow rate) due to scattering in all directions (the absence of a narrow radiation pattern of the probe radiation scattered by the particles); instability of readings due to the influence of temperature, fluctuation and other factors.

A known method of measuring the flow rate of liquid media, including sounding the cross section of the flow with acoustic cylindrical waves, detecting reflected cylindrical waves and measuring their frequency, registering secondary vibrations with a surface acoustic wave receiver offset from the center of the cylindrical transducer to the periphery, and measuring their frequency, wherein the flow rate determined by the difference of the measured frequencies [2]
The disadvantage of this method is the narrow range of measured costs.

 The technical result from the use of the invention is the expansion of the measurement range in the direction of low speeds of the medium.

This is achieved by the fact that they additionally emit a normal acoustic wave at a frequency corresponding to one of the critical components of the series ω _kr a ^-1 • (3.83; 7.02; 10.17; 13.32.) • s, where a is the acoustic the radius of the pipeline, with the speed of sound in the medium, the radiation frequency is changed until a new critical frequency is reached, the difference between the initial and new values of the radiation frequencies is measured, which determine the volumetric flow rate, the density of the medium is determined from the frequency of the reflected cylindrical waves, and the mass flow rate is computes the product of the volumetric flow rate by the density.

 The drawing 1 shows a variant of the functional diagram of a device that implements the method.

 The device comprises a pipeline section 1 with an acoustic wave emitter 2 on its outer surface, which creates normal waves in the medium of the internal volume of the section; receiving acoustic cylindrical transducer of normal waves 3, recording the passage of normal waves through section 1; receiving acoustic cylindrical transducer 4, detecting radial vibrations in section 1; an acoustic cylindrical transducer 5 operating sequentially in the modes of emission of short pulses, and then receiving after each pulse the reverberation waves created by it in the medium and intended for measuring the density of the medium; signal amplifiers 6; switch 7 with a bridge circuit; a regulator of "smooth" change of frequency 8 of the harmonic oscillation generator 9; information processing device 10; pulse generator 11 and frequency counter 12. To exclude the possibility of surface waves, acoustic traps 13 are used.

становится нераспространяющейся, т. е. ее продольная составляющая

0, а радиальная принимает одно из критических максимальных значений: m a^-1(3,83; 7,02;). В результате, на снабженный мостовой схемой коммутатор 7 после усиления в 6 будут поступать сигналы с преобразователя 4 и будет отсутствовать сигнал с преобразователя 3. В таких ситуациях мостовая схема коммутатора 7 сбалансирована, на регулятор 8 сигнал не поступает и генератор 9 подает на излучатель 2 сигналы прежней частоты ω $\genfrac{}{}{0ex}{}{\text{кр}}{\text{i}}$ . При появлении движения среды в трубопроводе, т. е. при V≠0, и при прежней частоте ω $\genfrac{}{}{0ex}{}{\text{кр}}{\text{i}}$ , длина волны λ, а с ней и волновое число К изменяется вследствие сноса потоком излучения:

. Изменение длины волны приведет к "отпиранию" трубопровода и нормальные волны, пройдя участок 1, попадают на преобразователь 3, после усиления в 6 поступают на коммутатор 7. Амплитуда радиальной составляющей колебаний среды, регистрируемая преобразователем 4, уменьшится. Произойдет разбалансировка мостовой схемы коммутатора 7, с выхода которого на регулятор 8 поступает усиленный в 6 сигнал и частота генератора 9 начинает изменяться. При этом изменяется длина и волновое число нормальной волны в трубопроводе и при

трубопровод вновь запирается. Сбалансированный мост коммутатора 7 приводит к закрытию его выхода на регулятор 8; генератор 9 продолжает возбуждение излучателя 2 на частоте ω $\genfrac{}{}{0ex}{}{\text{кр}}{\text{i+1}}$ . Одновременно коммутатор 7 открывает канал передачи информации с выходов преобразователей 3, 4 на устройство 10, осуществляющее расчет и выдающего информацию о скорости потока (объемном расходе). При последующих изменениях скорости движения подобная процедура повторяется до нового критического значения частоты

и т.д. (знак ± определяется направлениями векторов

).A method for measuring the flow rate of liquid and gaseous media based on the waveguide properties of the pipeline section is as follows. From the output of the harmonic oscillation generator 8, the electric harmonic oscillation signal is supplied to the acoustic transducer 2, which also emits a harmonic signal passing through the wall of the pipeline 1 into the medium filling the pipeline. The oscillation frequency of normal waves at a medium velocity V 0 is chosen equal to the value of one of the critical components of the series: ω _kr a ^-1 (3.83; 7.02; 10.17; 13.32.) • with _o obtained from the sequence zeros of the Bessel function of the condition: I ₁ (ma) 0, where a is the inner radius of the pipeline section 1; m ω $\genfrac{}{}{0ex}{}{\text{rh}}{\text{i}}$ • Co, with _{o the} speed of sound in the laboratory coordinate system at V 0. At a frequency ω = ω $\genfrac{}{}{0ex}{}{\text{cr}}{\text{i}}$ normal wave with wave vector

becomes non-proliferating, i.e., its longitudinal component

0, and the radial takes one of the critical maximum values: ma ^-1 (3.83; 7.02;). As a result, to the switch 7 equipped with a bridge circuit, after amplification of 6, signals from the converter 4 will be received and there will be no signal from the converter 3. In such situations, the bridge circuit of the switch 7 is balanced, the signal is not supplied to the regulator 8, and the generator 9 sends signals to the emitter 2 previous frequency ω $\genfrac{}{}{0ex}{}{\text{cr}}{\text{i}}$ . When medium flows in the pipeline, i.e., at V ≠ 0, and at the same frequency ω $\genfrac{}{}{0ex}{}{\text{cr}}{\text{i}}$ , the wavelength λ, and with it the wave number K, changes due to drift by the radiation flux:

. Changing the wavelength will lead to the "unlocking" of the pipeline and normal waves, passing section 1, fall on the transducer 3, after amplification of 6 go to the switch 7. The amplitude of the radial component of the oscillations of the medium, recorded by the transducer 4, will decrease. There will be an imbalance in the bridge circuit of the switch 7, from the output of which a signal amplified in 6 is supplied to the regulator 8 and the frequency of the generator 9 starts to change. In this case, the length and wave number of the normal wave in the pipeline and at

the pipeline is again blocked. The balanced bridge of the switch 7 leads to the closure of its output to the regulator 8; the generator 9 continues the excitation of the emitter 2 at a frequency ω $\genfrac{}{}{0ex}{}{\text{cr}}{\text{i + 1}}$ . At the same time, the switch 7 opens a channel for transmitting information from the outputs of the converters 3, 4 to the device 10, which calculates and provides information on the flow rate (volume flow). With subsequent changes in speed, this procedure is repeated until a new critical frequency value

etc. (the sign ± is determined by the directions of the vectors

)

[1]
где Q объемный расход, а радиус трубопровода на участке измерения 1, Δω^кр = ω $\genfrac{}{}{0ex}{}{\text{кр}}{\text{i+1}}$ - ω $\genfrac{}{}{0ex}{}{\text{кр}}{\text{i}}$ ; (i 1, 2, 3.).The static characteristic of the device is

[1]
where Q is the volumetric flow rate and the radius of the pipeline in the measuring section 1, Δω ^cr = ω $\genfrac{}{}{0ex}{}{\text{cr}}{\text{i + 1}}$ - ω $\genfrac{}{}{0ex}{}{\text{cr}}{\text{i}}$ ; (i 1, 2, 3.).

[2]
где γ = C_p•C $\genfrac{}{}{0ex}{}{\text{-1}}{\text{v}}$ ;; C_p, C_v теплоемкости; β_из изотермическая сжимаемость среды.To determine the mass flow rate Q _m = Qρ, where ρ is the density of the medium, the density of the medium r is previously measured. This is done either by transducer 4, or by the same transducer 5, but installed outside of section 1. In the first case, transducer 4, in addition to the function of a radial vibration meter, performs the function of a density meter in the time interval for establishing critical frequencies. In the second case, the transducer 5 measures only the density of the medium, which in many cases is preferable. In both cases, when determining the density, the transducer 4 (5) sequentially performs the functions of a transmitter and then a signal receiver. To this end, from the output of the pulse generator 11, the signals in the form of short pulses arrive at the transducer 5, which radiates into the medium cylindrical waves propagating to the cylindrical axis of the transducer, and after the front of the wave rotates on this axis in the opposite direction from the axis to the inner wall; then, after reflection from it, cylindrical waves converging to the axis again form, etc. As a result, a sequence of reverberation waves is created inside the converter inside the medium (15 20 or more, depending on the amplitude, pulse duration, radius a, medium properties, etc. /, the frequency of which is measured by the frequency meter 12 and is proportional to the density of the medium:

[2]
where γ = C _p • C $\genfrac{}{}{0ex}{}{\text{-1}}{\text{v}}$ ;; C _p , C _v heat capacity; β _from isothermal compressibility of the medium.

 Information about the frequency from the output of the frequency counter 12 enters the device 10, which after calculating by the formulas [1 3] provides information about the density, volume and mass flow rates.

[3]
и не зависит (при β_из- const-const) от скорости звука в среде С_o.The static characteristic of the mass flow meter is:

[3]
and does not depend (for β _from - const-const) on the speed of sound in a medium With _o .

 The application of the proposed method for measuring the flow rate of liquid and gaseous media allows to measure the mass flow rate and increase the measurement accuracy due to the following factors: the measured quantity is the frequency, the measurement accuracy of which is extremely high and becomes even higher when using high critical frequencies; use as sounding normal waves propagating without distortion; eliminating the effects of the absolute speed of sound in the medium on the accuracy of measuring the mass flow, because the speed of sound and the changes that determine it - there is no temperature factor; probing radiation coverage of all points of the radial cross-sectional area of the measured medium flow.

 A significant advantage of the proposed method is the ability to measure small velocities of the medium that are not accessible by ultrasonic and other methods of measuring speed (flow).

Claims (1)

A method for measuring the mass flow rate of liquid and gaseous media, including sensing the cross section of the flow with acoustic cylindrical waves, registering the reflected cylindrical waves and measuring their frequency, as well as determining the flow rate, characterized in that the normal acoustic wave is additionally emitted into the medium flow at a frequency corresponding to one of the critical components of the series ω _cr a ^{- 1} x / 3.83; 7.02; 10.17; 13.32; / xc, where a is the acoustic radius of the pipeline, c is the speed of sound in the medium, the radiation frequency is changed until a new critical frequency is reached, the difference between the initial and new values of the critical radiation frequency is measured, from which the volume flow is determined, the density of the reflected cylindrical waves is determined by the density medium, and the mass flow rate is calculated as the product of volumetric flow rate and density.