CN102735587A - Jet flow density measurement device and method - Google Patents

Abstract

The invention discloses a jet density measuring device and method. Including flow inlet, inlet joint, cover plate, jet oscillating element, dynamic differential pressure high pressure tube, jet nozzle, jet wall, jet feedback loop, dynamic differential pressure low pressure tube, outlet joint, flow outlet; jet oscillating element The plane where it is located is perpendicular to the flow inlet and outlet; the dynamic differential pressure between the two pressure-taking pipes is measured by the dynamic differential pressure sensor, and then input to the secondary instrument through the line for density measurement. In the present invention, after the fluid enters the jet oscillating element through the inlet, the cavity is induced to oscillate due to the Coanda effect and the feedback loop of the fluid; the differential pressure measured by the dynamic differential pressure sensor is an oscillating pulsating differential pressure, and the oscillation of the differential pressure The frequency is proportional to the flow rate of the jet nozzle, and the average value of the differential pressure is proportional to the dynamic pressure head of the fluid at the jet nozzle. Then, the ratio of the dynamic pressure head to the square of the flow velocity is proportional to the density of the medium. The invention has the advantage that it can realize the density measurement of the flowing medium at a low Reynolds number.

Description

Device and method for measuring jet density

technical field

The invention relates to a density measuring device, in particular to a jet density measuring device and method applicable to the density measurement of flowing gas or liquid, and belongs to the technical field of fluid measurement.

Background technique

Density meters are widely used in petroleum, natural gas measurement, chemical and printing industries; the existing densitometers include Coriolis flow densitometers, differential pressure densitometers, radioactive densitometers, oscillating tube densitometers, etc.; The flow density meter has high accuracy but is expensive, and has high requirements on the cleanliness of the medium; the differential pressure density meter is mostly used in oil density measurement, which can be used for liquid measurement but cannot be used for gas density measurement; There are certain potential safety hazards for radioactive sources; the oscillating tube density meter requires self-excited Karman vortex oscillation of the cylinder, and Karman vortex oscillation has a lower limit of Reynolds number, that is, when the flow rate is lower than a certain Reynolds number, Karman vortex street will not be generated , the density cannot be measured.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the shortcomings of existing density measurement methods, and provide a low Reynolds number tube flow jet density measurement method and a measurement device.

A jet density measuring device, characterized in that it includes a cover plate and a jet oscillating element; the jet oscillating element includes an inlet channel, a jet nozzle, an intermediate channel, and an outlet channel from front to back, wherein the jet outlet and the jet nozzle There are also two jet feedback loops between them; the above-mentioned middle flow channel is in the form of gradual expansion from front to back; the above-mentioned cover plate is installed on the upper part of the jet oscillating element, and the cover plate is installed with an inlet joint connected with the above-mentioned inlet flow channel, and connected with the above-mentioned outlet The outlet joint with the flow channel connected; the inlet joint and the outlet joint are used to connect the medium pipeline to be measured; the above cover plate is also equipped with a dynamic differential pressure sensor high-pressure pressure tube extending into the jet nozzle and a dynamic differential pressure sensor extending into the jet outlet. Differential pressure sensor low pressure pressure tube.

The jet density measurement method using the jet density measurement device described in the right is characterized in that it comprises the following steps:

Step A, connecting the medium pipeline to be measured between the inlet joint and the outlet joint; allowing the jet to pass through the jet oscillating element to generate an oscillating jet;

Step B, using the dynamic differential pressure sensor high pressure pressure tube and the dynamic differential pressure sensor low pressure pressure tube to measure the pressure difference between the jet nozzle and the jet outlet of the jet oscillating element;

Step C, calculate the density of the jet according to the following formula:

ρ =K*(DP/f ² ),

In the formula, ρ represents the density of the jet; DP represents the average pressure difference between the jet nozzle and the jet outlet of the jet oscillating element; f represents the oscillation frequency of the jet; K is the proportional coefficient, which is a fixed value for a specific jet oscillating element, It is pre-calibrated according to the experiment; the oscillation frequency f of the jet is obtained by the following method: dynamically record the change value of the differential pressure sensor over time, apply fast Fourier transform to convert the time domain signal into a frequency domain signal, and obtain the oscillation frequency.

The oscillation frequency of the jet is obtained by the following method: dynamically record the value of the differential pressure sensor over time, apply fast Fourier transform to convert the time domain signal into a frequency domain signal, and obtain the oscillation frequency (refer to He Zhenya, digital signal processing Theory and Application, Beijing: People's Posts and Telecommunications Press, Beijing, 1983). By using the measured pressure difference between the jet nozzle and the jet outlet, the oscillation frequency of the jet is obtained through calculation, without setting a separate oscillation frequency measurement component, which simplifies the structure and reduces the cost.

The jet density meter involved in the invention can greatly reduce the lower limit of the measured Reynolds number, has simple structure and low cost. The fluid medium flows through the jet oscillating element (refer to Cai Wuchang, Ying Qijia, New Flow Measuring Instrument, Beijing: Chemical Industry Press, Beijing, 2006), and an oscillating differential pressure signal is formed between the jet inlet and outlet, through The density measurement of the flowing medium can be carried out by collecting a dynamic differential pressure signal. Compared with the prior art, the present invention can realize fluid density measurement of liquid and gas, the measurement proportional coefficient K of liquid and gas is consistent, and the lower limit of the measurable Reynolds number of the present invention is lower, the measuring device has simple structure and low cost.

Description of drawings

FIG. 1 is a schematic structural diagram of the present invention; FIG. 2 is a top view of the jet oscillating element 4 .

The meanings of each label are as follows: 1 flow inlet, 2 inlet joint, 3 cover plate, 4 jet oscillating element, 5 dynamic differential pressure high pressure pressure tube, 6 jet nozzle, 7 jet attached wall, 8 jet feedback loop, 9 dynamic differential pressure Low pressure pressure pipe, 10 outlet joint, 11 flow outlet, 12 inlet channel, 13 intermediate channel, 14 outlet channel, 15 jet outlet.

Detailed ways

The technical scheme of the present invention is described in detail below in conjunction with accompanying drawing:

An embodiment of the jet density measuring device of the present invention is shown in Fig. 1, and it comprises: flow inlet 1, inlet joint 2, cover plate 3, jet oscillating element 4, dynamic differential pressure high-pressure take-off tube 5, jet nozzle 6, jet flow Attached wall 7, jet feedback loop 8, dynamic differential pressure low-pressure pressure taking pipe 9, outlet joint 10, flow outlet 11, inlet flow channel 12, intermediate flow channel 13, outlet flow channel 14, jet outlet 15, of which the jet oscillating element 4 Including jet nozzle 6, jet attachment wall 7, jet feedback loop 8, dynamic differential pressure low-pressure pressure pipe 9, outlet joint 10, flow outlet 11, inlet flow channel 12, intermediate flow channel 13, outlet flow channel 14, jet outlet 15 . The upper port of the inlet joint 2 is the flow inlet 1, which can be connected to the fluid pipeline to be measured through a hose. The lower end of the inlet joint 2 is tightly connected with the cover plate 3 through threads, and the lower end of the outlet joint 10 is also threaded tightly with the cover plate 3. Fixed connection, the upper end of the outlet joint 10 is a flow outlet, which can be connected back to the medium pipeline to be measured through a hose connection; the cover plate 3 is covered on the jet oscillating element 4 and is fixedly connected with it by bolts; the jet oscillating element 4 The jet nozzle 6 is provided with a dynamic differential pressure high-pressure pipe 5 , and the jet outlet 15 of the jet oscillating element 4 is provided with a dynamic differential pressure low-pressure pipe 9 .

When performing density measurement, the above-mentioned measuring device is connected to the flow pipeline of the fluid to be measured with a hose through the inlet joint 2, and the fluid enters the jet oscillating element 4 from the flow inlet 1, and the main jet coming out of the jet nozzle 6 is caused by the Coanda effect Deviated to one side of the jet wall 7, the main jet flows out through the jet outlet 15 of the jet oscillating element 4, and a small part of the jet returns to the jet nozzle 6 through the jet feedback loop 8 on the same side, pushing the main jet to deflect the other side. wall, a small part of the jet flows to the jet nozzle 6 through the jet feedback loop on the other side; so that the cycle continues to form cavity oscillation. A dynamic differential pressure sensor is used to measure the differential pressure between the high-pressure pressure pipe 5 and the low-pressure pressure pipe 9 in real time, and the measured data is calculated according to the following formula and the density of the output jet is displayed:

ρ =K*(DP/f ² ),

In the formula, ρ represents the density of the jet; DP represents the average value of the pressure difference output by the differential pressure sensor; f represents the oscillation frequency of the jet, which is obtained by the following method: dynamically record the value of the differential pressure sensor over time, and apply fast Fourier Leaf transform converts the time-domain signal into a frequency-domain signal to obtain the oscillation frequency (refer to He Zhenya, Theory and Application of Digital Signal Processing, Beijing: People's Posts and Telecommunications Press, Beijing, 1983); K is the proportional coefficient, for a specific jet oscillation Components, which are fixed values, are pre-calibrated according to experiments.

In order to make the public easy to understand the technical solution of the present invention, the measurement principle of the present invention is described in detail below:

Theoretical studies and experiments have proved that the frequency f of cavity oscillation induced by the Coanda effect of the jet and the feedback loop is proportional to the flow velocity v at the jet nozzle, the formula is as follows:

v = k ₁ * f (1)

Wherein, k ₁ is a proportional coefficient; the oscillation frequency f can be obtained by using the existing detection elements such as heat-sensitive, force-sensitive, and optical fibers near the feedback channel or the entrance and exit to detect the jet oscillation frequency, and the present invention is to simplify the structure , using the method of fast Fourier transform on the dynamic differential pressure signal, specifically to dynamically record the change value of the differential pressure sensor over time, apply the fast Fourier transform to convert the time domain signal into a frequency domain signal, and obtain the oscillation frequency (Refer to He Zhenya, Theory and Application of Digital Signal Processing, Beijing: People's Posts and Telecommunications Press, Beijing, 1983).

The average value DP of the dynamic differential pressure signal is proportional to the dynamic pressure head ^ρv2 at the jet nozzle, and the formula is as follows:

ρv ² =k ₂ *DP (2)

Wherein, k ₂ is proportionality coefficient; ρ is fluid density;

Formula (3) can be obtained from formula (1) and formula (2) as follows:

ρ=(k ₂ /k ₁ ² )*(DP/f ² ) (3)

The density of the fluid is ρ, let the value of k ₂ /k ₁ be K, then there is formula (4):

ρ=K*(DP/f ² ) (4)

For a specific jet oscillating element, the proportional coefficient K is a fixed value, which can be pre-calibrated according to experiments.

Claims (2)

1. A jet density measuring device, characterized in that: Including a cover plate (3) and a jet oscillating element (4); The jet oscillating element (4) includes an inlet flow channel (12), a jet nozzle (6), an intermediate flow channel (13), and an outlet flow channel (14) from front to back, wherein the jet outlet (15) and the jet nozzle (6 ) also has two jet flow feedback loops (8); the above-mentioned middle flow channel (13) is in the form of gradual expansion from front to back; The above-mentioned cover plate (3) is installed on the upper part of the jet oscillating element (4), and the cover plate (3) is installed with an inlet joint (2) communicating with the above-mentioned inlet flow channel (12), and communicating with the above-mentioned outlet flow channel (14). The outlet joint (10); the inlet joint (2) and the outlet joint (10) are used to connect the medium pipeline to be measured; The above cover plate (3) is also equipped with a dynamic differential pressure sensor high pressure pressure tube (5) extending into the jet nozzle (6) and a dynamic differential pressure sensor low pressure pressure tube (9) extending into the jet outlet (15) . 2. utilize the jet density measuring method of the described jet density measuring device of claim 1, it is characterized in that comprising the following steps: Step A. Connect the medium pipeline to be measured between the inlet joint (2) and the outlet joint (10); make the jet flow pass through the jet oscillation element (4) to generate an oscillating jet; Step B. Use the high-pressure pressure-taking end (5) of the dynamic differential pressure sensor and the low-pressure pressure-taking tube (9) of the dynamic differential pressure sensor to measure the pressure difference between the jet nozzle (6) and the jet outlet (15) of the jet oscillation element (4) ; Step C, calculate the density of the jet according to the following formula: ρ =K*(DP/f ² ), In the formula, ρ represents the density of the jet; DP represents the average pressure difference between the jet nozzle and the jet outlet of the jet oscillating element; f represents the oscillation frequency of the jet; K is the proportional coefficient, which is a fixed value for a specific jet oscillating element, Obtained according to the pre-calibration of the experiment; The oscillation frequency f of the jet is obtained by the following method: dynamically record the value of the differential pressure sensor over time, and apply fast Fourier transform to convert the time domain signal into a frequency domain signal to obtain the oscillation frequency.

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