Spiral liquid film velocity measurement sensor and method based on electrolyte tracer method

Abstract

The present invention relates to a spiral annular flow liquid film velocity measurement sensor for electrolyte tracing method, comprising: a measurement pipeline, an upstream electrode group and a downstream electrode group fixed on the inner wall of the measurement pipeline, and an electrolyte injection hole, wherein the measurement pipeline is a non-conductive measurement pipeline, the upstream electrode group and the downstream electrode group respectively include a plurality of electrode pairs distributed around the measurement pipeline, each pair of electrodes is divided into an excitation end and a receiving end, and is used to detect the resistivity change of a local liquid film; the electrolyte injection hole is arranged at a position close to the upstream electrode group. The present invention also provides a spiral liquid film velocity measurement method based on the electrolyte tracing method implemented by using the sensor.

Description

Technical Field

[0001] The invention belongs to the technical field of gas-liquid two-phase flow measurement, and relates to a device and method for measuring the velocity of a spiral annular flow liquid film. Background Art

[0002] Spiral annular flow is commonly found in many industrial fields such as turbines, separators, and combustion chambers. In recent years, spiral annular flow has also been used in oil and gas wellhead measurements. Spiral annular flow is similar to straight tube annular flow, in that both are liquid films flowing on the tube wall, and the center of the pipe is a high-speed flowing gas core. Compared with straight tube annular flow, spiral annular flow has fewer entrained droplets, and the spiral liquid film has both axial velocity and tangential velocity components. After flowing out of the spiral flow generating device, the spiral annular flow has an attenuation characteristic, that is, as the flow distance changes, the tangential velocity will gradually decay with the two-phase flow, and there is a tendency to return to straight tube flow. Based on the above factors, the measurement complexity of the spiral liquid film velocity is much more difficult than that of the straight tube liquid film velocity. The commonly used methods for measuring the liquid film velocity in straight tube annular flow include electrical method, ultrasonic method, high-speed camera method, laser induced fluorescence imaging (PLIF), etc., and then the liquid film velocity is measured by using the similarity of liquid film fluctuations and signal processing techniques such as tracing or cross-correlation.

[0003] Compared with the measurement of liquid film velocity in a straight tube annular flow, there are three technical difficulties in measuring the velocity of a spiral liquid film:

[0004] 1. Due to the existence of centrifugal force, the disturbance wave of the liquid film interface in the spiral annular flow will be suppressed to a certain extent, making it less obvious than the disturbance wave of the liquid film in the straight tube;

[0005] Second: The tangential momentum of the unforced spiral annular flow will decay as the flow distance increases, that is, the flow direction of the spiral liquid film changes with the position, making it difficult to measure the liquid film flow velocity using the upstream and downstream signal cross-correlation method;

[0006] 3. Since the spiral annular flow is not a fully developed flow, its gas-liquid turbulence is relatively strong. When the gas-liquid flow rate is high, the fluctuating interface and the small bubbles mixed in will form spiral streamlines, resulting in extremely poor transparency of the spiral liquid film. Figure 1 shown.

[0007] Due to the complexity of the spiral liquid film, there are very few methods for measuring the axial velocity and tangential velocity of the annular flow at the same time. The disclosed invention patent CN 107101681 A uses high-speed photography to mix small gas bubbles into the liquid film as natural tracer particles, and measures the bubble velocity by the bubble trajectory length and exposure time taken by the high-speed camera, and regards it as the spiral liquid film velocity. Obviously, when the gas-liquid two-phase flow velocity is high, the bubble tracing effect will deteriorate, and the tiny bubbles in the liquid film are difficult to be captured by the high-speed camera. The disclosed invention patent CN104121955A uses different ultrasonic probe distribution methods to measure the average flow velocity and total flow rate of the liquid-liquid spiral flow liquid film. However, the propagation of sound waves will be affected by temperature, and when the turbulence on the surface of the liquid film is strong, the reflected ultrasonic signal of the phase interface will also have strong noise, and these errors are difficult to compensate and correct. Summary of the invention

[0008] In order to overcome the above measurement objectives and the shortcomings of existing technical methods, the present invention proposes a spiral liquid film velocity measurement device and method based on the conductivity method. In order to achieve the simultaneous measurement of the axial velocity and tangential velocity of the spiral liquid film, the electrolyte tracer method and the circumferential multi-electrode distribution scheme are adopted. The technical scheme is as follows: To achieve the above purpose, the present invention specifically adopts the following technical scheme:

[0009] A spiral annular flow liquid film velocity measurement sensor for an electrolyte tracer method comprises: a measuring pipeline, an upstream electrode group and a downstream electrode group fixed on the inner wall of the measuring pipeline, and an electrolyte injection hole, wherein the measuring pipeline is a non-conductive measuring pipeline, the upstream electrode group and the downstream electrode group respectively include a plurality of electrode pairs distributed around the measuring pipeline, each pair of electrodes is divided into an excitation end and a receiving end, and is used to detect the resistivity change of a local liquid film; the electrolyte injection hole is arranged at a position close to the upstream electrode group.

[0010] Furthermore, let D be the inner diameter of the measuring pipe, and the centerline distance between the upstream electrode group U and the downstream electrode group D be L x , L x Between 0.5D-10D.

[0011] Furthermore, the width W of each electrode is 0.002m-0.010m; and the midline distance L' between the excitation end and the receiving end of each electrode pair is 0.003m-0.020m.

[0012] The present invention also provides a spiral liquid film velocity measurement method based on the electrolyte tracing method implemented by the sensor. The electrolyte solution is injected into the front injection hole of a certain electrode pair of the upstream electrode group. After the injection, the signal measured by this electrode pair of the upstream electrode group will mutate. As the spiral annular flow liquid film flows, the electrode pair in the downstream electrode group where the signal also mutates and the amplitude of the change is the largest is found. The time difference between the two signal mutations is the time of liquid film movement. The axial velocity and tangential velocity of the spiral annular flow liquid film are obtained as follows:

[0013] u l =L x / Δt

[0014] w l =L θ / Δt

[0015] In the formula, Lx, L θ They are respectively the axial distance and circumferential distance of the fluid flowing through the velocity sensor, m; Δt represents the time of the liquid film movement measured by the spiral annular flow liquid film velocity measurement sensor, s. Axial velocity u l and the tangential velocity w l The unit is m / s. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The spiral annular flow liquid film under the high-speed camera, the working condition is the gas phase apparent flow velocity U SG =15m / s, volume liquid fraction LVF=1%.

[0017] Figure 2 This is a schematic diagram of a spiral annular flow velocity measurement sensor. The sensor itself is made of non-conductive material.

[0018] Reference numerals: 1 - injection hole; 2 - upstream electrode group; 3 - downstream electrode group; 4 - non-conductive measuring pipe

[0019] Figure 3 The figure is a schematic diagram of the spiral annular flow velocity measurement system, which is mainly composed of an excitation module, a receiving module, a signal conversion module, a signal conditioning module, a host computer, and a data acquisition module.

[0020] Figure 4 This is a signal processing flow chart of the spiral annular flow velocity measurement device.

[0021] Figure 5 Collect the original signal graph for the spiral annular flow velocity measurement device.

[0022] ( Figure 5 Experimental conditions: pressure 0.1MPa; volume water content 2%; gas phase apparent velocity: 10m / s, three injections of electrolyte solution)

[0023] Figure 6 It is the time difference of upstream and downstream signal mutation after electrolyte injection.

[0024] Figure 7 When the gas phase apparent velocity is 12m / s and the volume liquid content varies from 0-3%, the spiral annular flow velocity measurement system measures the average axial velocity of the liquid film at different positions in the pipeline. X = nR is the distance from the tail end of the vortexer, which is n*R, n is a positive real number, and R is the radius of the pipeline.

[0025] Figure 8 When the gas phase apparent velocity is 12m / s and the volume liquid content varies from 0-3%, the spiral annular flow velocity measurement system measures the average tangential velocity of the liquid film at different positions in the pipeline.

[0026] Fig. 9 When the gas phase apparent velocity is 12m / s and the volume liquid content varies from 0-3%, the difference between three different measurement results of the average axial velocity of the liquid film measured by the spiral annular flow velocity measurement system at a position 4 times the pipe diameter away from the tail end of the vortexer and the average value is the repeatability measurement result of the average axial velocity of the liquid film.

[0027] Fig.10 When the gas phase apparent velocity is 12m / s and the volume liquid content varies from 0-3%, the difference between three different measurement results of the average tangential velocity of the liquid film measured by the spiral annular flow velocity measurement system at a position 4 times the pipe diameter away from the tail end of the vortexer and the average value is the repeatability measurement result of the average tangential liquid film velocity. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the accompanying drawings.

[0029] The present invention is a device for measuring the velocity of a liquid film of a spiral annular flow in industry. Different from the previous devices and methods for measuring the velocity of a liquid film, the present invention solves the problem of simultaneously measuring the axial velocity and the tangential velocity of a spiral liquid film through the electrolyte tracer method and the multi-electrode design. The design principle is simple, the installation is convenient, and no complex algorithm compensation is required, so the device has a wider applicability.

[0030] The basic principle of the invention is that high-concentration electrolyte solution can cause a dramatic change in the local conductivity of the liquid film. The high-concentration electrolyte solution is used to mark the flow distance of the liquid film in the axial and tangential directions, and the liquid film velocity is calculated based on the time difference between the marked fluid and the upstream and downstream sensors.

[0031] Sensor principle diagram Figure 2As shown, the spiral annular flow liquid film velocity measurement sensor is mainly divided into 1-upstream electrode group (U), 2-downstream electrode group (D), 3-injection hole, 4-non-conductive measuring pipe. Multiple groups of conductivity electrodes are embedded in the inner wall of the measuring pipe to sense the change in conductivity. After the electrolyte is injected, the electrical signal between the transmitting electrode and the receiving electrode through which it flows will suddenly change due to the change in the local resistivity of the liquid film. The velocity measurement method proposed in the present invention is simple in principle, does not involve soft field effects, and does not need to consider the reflection and refraction of light waves, sound waves and other signals. When the gas-liquid two-phase flow rate is high and the turbulence is strong, it can still achieve accurate measurement of the axial flow rate and tangential flow rate of the liquid film.

[0032] The spiral annular flow velocity measuring device of the present invention can be installed horizontally, that is, the gas-liquid two-phase flow forms a spiral annular flow with an axial velocity component and a tangential velocity component after flowing through the swirler, and the measurement result can be obtained after passing through the velocity sensor. Multiple groups of spiral annular flow velocity measuring devices are installed in series, and the spiral annular flow liquid film velocity at any position in the pipe section can be measured by different sensor lengths and multiple sensor combination installation methods. The spiral annular flow velocity measuring device proposed by the present invention can be applied to spiral liquid film velocity measurement in various installation methods such as horizontal installation, vertical installation, and inclined installation.

[0033] The spiral annular flow velocity measurement device proposed in the present invention is mainly divided into an excitation source, a velocity measurement sensor, a signal conversion module, a signal conditioning module, a host computer, and a data acquisition module. Figure 3 As shown. A certain concentration of electrolyte solution is injected through the injection hole 3 at the front end of the upstream electrode U1. After the injection, the signal measured by the upstream electrode will mutate. As the liquid film flows, the signal of a certain electrode pair of the downstream electrode D2 will mutate. The time difference between the two signal mutations is the time Δt of the liquid film movement. The axial distance of the liquid film flow is the midline distance L of the upstream and downstream electrode pairs. x The circumferential distance can be calculated based on the circumferential distance L between the upstream electrode and the downstream electrode corresponding to the injection point. θ There are 12 pairs of evenly distributed electrodes U1~U2 in the upstream of the sensor used in this experiment. 12 The centerline of each pair of electrodes is 30° apart. There are 18 pairs of electrodes evenly distributed downstream, D1~D 18 ,,The center line of each pair of electrodes is 20° apart. Inject electrolyte solution into the injection hole just above U1. Figure 5 The voltage signals of several groups of conductivity patches of the downstream D group electrodes were selected. The signals of the D8, D9, D10, and D11 electrodes all changed suddenly, and the change amplitude of the D8 electrode was the largest. This phenomenon is mainly due to the fact that the electrolyte concentration in the electrolyte solution is significantly higher than that of the measured liquid, and a certain degree of diffusion will occur. A large number of real flow experiments have proved that although there will be diffusion, there will definitely be a certain electrode whose measurement result is significantly higher than that of the adjacent electrode. θShould be:

[0034]

[0035] Since the liquid film itself is volatile and it takes a certain amount of time to inject a certain amount of electrolyte, the rising edge of the signal will fluctuate when the electrolyte is injected. To avoid the time error introduced by this problem, the Figure 4 The signal processing method pre-processes the signal, and the processed signal is as follows Figure 6 As shown, the time difference Δt is the difference between the non-zero starting points of the upstream and downstream:

[0036] Δt=t2-t1

[0037] The axial velocity and tangential velocity of the spiral annular flow liquid film can be obtained by the following formula:

[0038] u l =L x / Δt

[0039] w l =L θ / Δt

[0040] Figure 7 and Figure 8 The figures are respectively the average axial velocity and the average tangential velocity of the liquid film of the spiral annular flow at different positions of the swirler outlet at normal pressure and gas phase apparent velocity of 12m / s. As shown in the figure, at a fixed gas phase apparent velocity, both the axial velocity and the tangential velocity tend to increase with the increase of volume liquid content. When the flow distance gradually increases, the momentum loss caused by friction and the influence of gravity cause the tangential velocity in the flow direction to gradually decrease, while the axial velocity gradually increases. This is due to the conversion of gravitational potential energy and part of the rotational kinetic energy into axial kinetic energy, and the continuous attenuation of the tangential momentum of the spiral flow.

[0041] In this experiment, in order to ensure the reliability of the experimental data, data were collected three times at each experimental operating point. The repeatability of the measurement results is as follows: Fig. 9 and Fig.10 The repeatability of the measurement is calculated according to the following formula:

[0042]

[0043] In the formula, S represents the repeatability of each experimental operating point (S only represents repeatability in this formula), N represents the number of data measurements, in this paper N = 3, x i Indicates the value of each measurement, Indicates the average value of each experimental point. In the real flow experiment, the repeatability of the entire measurement is taken as the maximum repeatability of all experimental points. In this experiment, the repeatability of the measurement is 0.035m / s.

[0044] In addition, it is worth noting that since the upstream and downstream small conductivity electrodes themselves have a certain length and width, a certain error will inevitably be introduced in the measurement length, and the most unsatisfactory experimental result is that the signal mutation values ​​of the two or three downstream electrodes are equivalent, and the true position of the downstream receiving end signal point cannot be obtained, resulting in a measurement deviation of the tangential velocity. The following example will illustrate the measurement error that will be caused at this time. Taking the operating point where the gas phase apparent velocity is 20m / s and the volume liquid content is 3% as an example, the time differences of the three measurements are 30ms, 30ms, and 26ms respectively. We take the average time difference Δt of the three measurements as 28.67ms. Figure 2 As shown, assuming that the signal is received by the U1 electrode upstream, the actual position of the fluid micro-group traced by the electrolyte downstream is D 13 Electrode center, if the measurement reception cannot be distinguished due to serious electrolyte diffusion, it will be misjudged as D 12 or D 14 , then the error introduced at this time is:

[0045] The actual liquid film tangential velocity is:

[0046]

[0047] If the downstream electrode is misjudged as D 12 , the liquid film tangential velocity is:

[0048]

[0049] If the upstream electrode is misjudged as D 14 , the liquid film tangential velocity is:

[0050]

[0051] Therefore, the relative error of the electrode back-cutting speed measurement is, and the error is D 12 , the relative error of the liquid film tangential velocity is: 8%, and it is misjudged as D 14 , the relative error of the tangential velocity of the liquid film is: 8.27%. Therefore, even if the worst measurement result occurs, that is, the adjacent electrode pairs cannot be predicted, the relative deviation of the tangential velocity measurement can still be guaranteed to be within 10%. A large number of experiments have proved that when the concentration of the electrolyte solution is appropriate, this measurement result will hardly occur.

[0052] The above proves the feasibility of the spiral annular flow liquid film velocity measurement device and method of the electrolyte tracer method protected by this patent application.

Claims

1. A spiral annular flow liquid film velocity measurement sensor for electrolyte tracer method, comprising: A measuring pipeline, an upstream electrode group and a downstream electrode group fixed on the inner wall of the measuring pipeline and an electrolyte injection hole, wherein the measuring pipeline is a non-conductive measuring pipeline, the upstream electrode group and the downstream electrode group respectively include a plurality of electrode pairs distributed around the measuring pipeline, each pair of electrodes is divided into an excitation end and a receiving end, and is used to detect the resistivity change of the local liquid film of the gas-liquid two-phase spiral annular flow, and the electrolyte injection hole is arranged at a position close to the upstream electrode group; an electrolyte solution is injected into the front injection hole of a certain electrode pair of the upstream electrode group, after the injection, the signal measured by this electrode pair of the upstream electrode group will mutate, and as the spiral annular flow liquid film flows, the electrode pair whose signal also mutates and has the largest variation is found in the downstream electrode group, and the time difference between the two signal mutations is the time of liquid film movement, and then the axial velocity and tangential velocity of the spiral annular flow liquid film are obtained.

2. The spiral annular flow liquid film velocity measurement sensor according to claim 1, characterized in that: Assume D is the inner diameter of the measuring pipe, and the centerline distance between the upstream electrode group U and the downstream electrode group D is L. x , L x Between 0.5D-10D.

3. The spiral annular flow liquid film velocity measurement sensor according to claim 1, characterized in that: The width W of each electrode is 0.002m-0.010m; the center line distance L' between the excitation end and the receiving end of each electrode pair is 0.003m-0.020m.

4. The spiral liquid film velocity measurement method based on the electrolyte tracer method implemented by the sensor according to any one of claims 1 to 3, the axial velocity and tangential velocity of the spiral annular flow liquid film are obtained as follows: u l =L x / Δt w l =L θ / Δt In the formula, Lx, L θ They are respectively represented as the axial distance and circumferential distance of the fluid flowing through the velocity sensor, in meters; Δt represents the time of the liquid film movement measured by the spiral annular flow liquid film velocity measurement sensor, in seconds; the axial velocity u l and the tangential velocity w l The unit is m / s.

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