RU2073830C1 - Method of measurement of flow rate of liquid and gaseous media - Google Patents

Abstract

FIELD: flowmetering, measurement of flow rate of liquid and gaseous media by acoustic means. SUBSTANCE: cross-section of flow is probed by acoustic cylindrical waves, which are excited by a cylindrical transducer in the direction of the pipeline axis, repeatedly reflected reverberation waves are received, and their frequency is measured in the absence and presence of flow, flow rate is determined according to the difference of measured frequencies. EFFECT: facilitated procedure. 1 dwg

Description

 The invention relates to the field of flow measurement and can improve the accuracy of measuring the flow rate of liquid and gaseous media by sounding with acoustic waves.

 Known methods for determining the flow velocity by the Doppler shift in the frequencies of the probe radiation in acoustics and optics [1] The main disadvantages of the Doppler methods are: the need for the presence of particles scattering the probe radiation; significant error in the measurement of speed due to radiation scattering in all directions (lack of a narrow radiation pattern of the scattered radiation); instability of indications, due to the influence of temperature, fluctuation and other factors.

The closest analogue of the invention is a method of measuring the flow rate of liquid media, including sensing the cross section of the flow by acoustic cylindrical waves using a ring transducer in the radial direction to the axis of the pipeline, which alternates in the modes of radiation and reception, measuring their frequencies and determining the flow rate [2]
The disadvantage of this method is the inability to achieve high accuracy of measurement.

 The technical result from the use of the invention is to improve the accuracy of measurement.

 This is achieved by the fact that in the method of measuring the flow rate, including sounding the cross section of the flow with acoustic cylindrical waves, which excite the cylindrical transducer in the direction of the axis of the pipeline, receiving repeatedly reflected reverberating cylindrical waves and measuring their frequency, measuring the frequency in the absence and presence of flow, and the value flow rate is determined by the difference of the measured frequencies.

 The essence of the method is as follows. Signals of cylindrical waves propagating from the inner surface of the cylindrical emitter into the medium flow to its axis, and then after the front in the opposite direction, from the axis to its inner surface, a sequence of decaying reverberation waves occurs. The number of such waves can be more than 20 and depends on the amplitude of the external signal, its duration, shape, medium properties, flow regime, etc. When the medium moves through the pipeline with a speed of V, the speed of sound propagation changes depending on the value of V at a constant value of density and temperature. Due to this, the frequency of reverberation waves also changes. A measure of flow will be a value proportional to the change in the frequency of the reverberation waves, relative to the frequency in a stationary medium.

 One of the variants of the functional diagram of a device that implements the proposed method is shown in FIG. one.

 The device comprises a tank 1 filled with a measured medium, a valve 2 mounted on the pipeline 3, acoustic cylindrical transducers 4, 4 ', electric signal generators 5 and 5', switches 6 and 6 ', amplifiers 7 and 7', frequency meters 8 and 8 ' and a flow calculating device 9.

The method of measuring the flow rate of liquid and gaseous media is as follows. The medium flowing out of the tank 1 (see Fig. 1) with the tap 2 open over a portion of the cylindrical pipeline 3 is probed using a transducer 4 with acoustic signals in the form of cylindrical wave pulses with frequency modulation used to increase sensitivity. The transducer 4 performs alternately the functions of the emitter and receiver of acoustic signals and can be “laid on” consisting of two halves of the cylindrical transducer 4 superimposed on the external surface of the pipeline or inserted inside the pipe so that its inner surface and the inner surface of the pipe form a single cylindrical surface. The voltage supplied from the generator of electrical signals 5 to the converter 4 in the form of short pulses with high-frequency filling is converted into 4 acoustic signals of the same frequency, with the same high-frequency modulation, after which the output of the converter 4, which is already operating in the mode of receiving acoustic signals using the switch 6, connected to the input of amplifier 7. After amplification of the signals at 7, they arrive at the frequency meter 8, where the frequencies of the reverberation waves are measured at V ≠ 0, the frequency at V 0 is measured before opening to wound. It is assumed that the temperature of the medium during flow measurement does not change and is known. If the temperature of the medium cannot be kept strictly constant and, therefore, errors caused by the instability of the temperature are superimposed on the measurement results, the measurement scheme is complicated. In this case, to measure the flow rate, the second one, same as 1, is used, the converter 4 ', placed in the tank 1. In this case, external signals from the generators 5 and 5' are fed simultaneously to the converters 4 and 4 ', and the signals received by them the reverberation waves of frequencies ω and ω _o through the switches 6 and 6 'are received, after amplification in 7 and 7' to the frequency meters 8 and 8 'and then to the device 9, where the flow values are calculated to the formula (1) given below.

где Q расход,
d диаметр трубопровода,

отношение удельных теплоемкостей,
ω_o,ω частоты реверберационных колебаний при V 0 и V≠ 0, соответственно.The static characteristic of the device is:

where Q is the flow rate
d pipe diameter

specific heat ratio,
ω _o , ω are the reverberation frequencies at V 0 and V ≠ 0, respectively.

When using frequency modulation, instead of frequencies ω _o , ω, ω are substituted in (1) $\genfrac{}{}{0ex}{}{\text{*}}{\text{o}}$ = ω _o • n, ω ^* = ω • n ,, where n is the number of modulation oscillations in the pulse.

 The application of the proposed method for determining the flow rate of the medium will improve the accuracy of measuring the flow rate due to the following factors: coverage of all medium points on the radial cross-sectional area of the pipeline with probing radiation and thereby automatically adding the velocity values to each cross-section point, eliminating the influence of sound velocity changes due to temperature and other influences, increased sensitivity due to frequency modulation of sounding signals.

Claims (1)

 A method for measuring the flow rate of liquid and gaseous media, including sensing the flow cross section by acoustic cylindrical waves, which are excited by a cylindrical transducer in the direction of the pipeline axis, receiving repeatedly reflected cylindrical reverberation waves and measuring their frequency, characterized in that the frequency of the reverberating waves is measured in the absence and at the presence of flow, and the flow rate is determined by the difference of the measured frequencies.