CN108181357B

CN108181357B - Vertical rotational flow split-phase capacitance integrated water content measuring device

Info

Publication number: CN108181357B
Application number: CN201810088701.3A
Authority: CN
Inventors: 徐英; 汪晶晗; 张涛; 李继良
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2018-01-30
Filing date: 2018-01-30
Publication date: 2020-09-15
Anticipated expiration: 2038-01-30
Also published as: CN108181357A

Abstract

The invention relates to a vertical rotational flow phase separation capacitance integrated water content measuring device, which comprises an outer pipe wall and an inner electrode, wherein the inner wall of the outer pipe wall is a metal inner wall and is used as an outer electrode.

Description

Vertical rotational flow split-phase capacitance integrated water content measuring device

Technical Field

The invention belongs to the technical field of flow measurement of moisture two-phase flow, and relates to a vertical rotational flow split-phase capacitance integrated water content measuring device.

Background

Moisture is widely present in nature and in various fields of industrial production. The liquid phase volume fraction is one of the important parameters of the moisture, so that the accurate measurement of the moisture is realized, the measurement precision of the flow is directly influenced, and the method has important significance on industrial production and scientific research. In practical application, the gas-liquid two-phase flow is complex and changeable, so that the accurate measurement of the volume fraction of the liquid phase is difficult. With the development of science and technology, tracing technology, ray technology, nuclear magnetic resonance technology, capacitance technology and the like are all applied to the measurement of the water content. However, the representativeness of the tracer sampling, the safety of the radiation and the structural complexity and high cost of nuclear magnetic resonance limit the use of these new techniques. As a relatively mature technology, the current research has gained a great deal of experience in capacitor construction, but it cannot be ignored that the response of a capacitive sensor, whether contact or non-contact, depends largely on the spatial distribution of the fluid, resulting in the measurement result being influenced by the flow pattern.

Chinese patent ZL 201710465819.9 and Chinese patent ZL 201710465822.0 propose a moisture content measuring device that measurement accuracy is high, including being located the overhead and having a rotatory phase separation unit and being located the capacitance measurement unit of lower part. The two parts of the device are separated, so the whole structure is long; in addition, experiments prove that when the gas phase flow rate is less than 10m/s and the liquid phase volume content is higher than 4%, the stability of the gas-liquid two-phase flow form after the spiral phase separation unit finishes entering the measuring unit cannot be ensured, so that the error between the water content measured value and the experiment given reference standard value is increased from 0.5% to 2%.

Disclosure of Invention

The invention aims to overcome the problems in the prior art, and provides a vertical rotational flow phase-splitting capacitance integrated water content measuring device, which integrates a rotational flow phase-splitting unit and a capacitance measuring unit into a whole, realizes gas-liquid phase-splitting distribution and constructs a capacitor to complete the measurement of the water content at the same time, and adopts the following technical scheme:

the utility model provides a vertical whirl split-phase electric capacity integral type contains water measuring device, including outer pipe wall and inner electrode, the inner wall of outer pipe wall is the metal inner wall, as the outer electrode, its characterized in that, be fixed with the metal inner electrode in the middle part of outer pipe wall, the cladding has the insulating layer in the outside of metal inner electrode, still be fixed with helical blade in the periphery of metal inner electrode and insulating layer, be equipped with the slant entry on the outer pipe wall, the tangential angle of slant entry is the same with helical blade's helix angle for fluid follows the tangential angle and gets into the space between helical blade and the outer pipe wall, the length of inner electrode is the length of electric capacity measurement section.

Preferably, the lead angle of the helical blade is between 10 and 50 degrees. The uppermost end of the metal inner electrode is at least one pitch away from the inclined inlet. The number of the swirl blades is 2-10. And D is the inner diameter of the flow channel, 0.3-3D is the inner diameter of the outer pipe wall, and 1-5D is the length of the capacitance measuring section. The diameter ratio of the inner electrode to the outer electrode is 1: 2-1: 10. The entrance slant length is not shorter than 3D.

Compared with the prior art, the invention has the following technical effects:

(1) the invention integrates the rotational flow phase splitting and the capacitance measurement, thereby ensuring the phase splitting distribution of gas and liquid and shortening the whole structure length;

(2) the gas phase and the liquid phase tangentially flow into the rotational flow split-phase section along the inclined inlet, and the flow direction and the state of the fluid are changed by the flow guiding effect of the threads. The liquid phase, due to its high density, moves circularly under the action of centrifugal force and simultaneously passes through the gas phase and is thrown to the pipe wall. Thereby realizing the split-phase flow state of gas phase concentrated in the central area and liquid phase along the pipe wall, and overcoming the defect of an inlet

Flow patterns interfere with the phase fraction measurement. After more than 1 circle of helical blades, the gas-liquid distribution is basically stable and can be used as a measuring section;

(3) in the measuring section, gas-liquid phases are continuously kept in split-phase distribution under the action of the thread blades, and meanwhile, the outer metal pipe wall and the conductive liquid film jointly form an outer electrode which interacts with the inner electrode to form a capacitor. Because the change of the gas-liquid two-phase content directly affects the thickness of a liquid film on the pipe wall, namely the distance between the inner electrode and the outer electrode is changed, the capacitance value is changed, and the capacitance moisture measurement only related to the liquid phase volume content is realized;

(4) after the measuring section is finished, the device can be connected with a straight pipe with any pipe diameter through the diameter expanding pipe, and the height of the whole device can be adjusted by changing the length of the diameter expanding pipe;

(5) the capacitance sensor is used for directly measuring the volume percentage of the liquid phase, the capacitance measurement precision is high, and the water content measurement accuracy is good;

(6) the invention selects the inclined inlet, on one hand, the inclined angle is the same as the lead angle of the thread blade, on the other hand, the area of the inlet is the same as the flow area of the fluid in the rotational flow phase-splitting section, thereby ensuring the flow stability of the moisture at the inlet and reducing the pressure loss;

(7) the device does not need to be separated, does not depend on a radioactive technology and a tracing technology to measure the moisture liquid phase content, and has simple structure, safety and reliability.

Drawings

FIG. 1 is a schematic structural diagram of a vertical cyclone phase separation capacitance integrated water content measuring device.

FIG. 2 shows the gas-liquid velocity distribution in the cyclone phase separation section.

(simulation experiment conditions: pressure 1.2MPa, water content 15%, gas phase apparent flow rate 10m/s)

FIG. 3 is a liquid phase volume distribution cloud chart in the cyclone phase separation section.

(simulation experiment condition: pressure 1.2MPa, water content range 5-15%, gas phase apparent flow rate 10m/s)

FIG. 4 is a graph of volume fraction versus cross-sectional fraction for different liquid phases.

(simulation experiment conditions: pressure 1.2MPa, water content range 1-20%, gas phase apparent flow rate 5m/s)

FIG. 5 is a graph of capacitance versus liquid volume fraction.

(simulation experiment conditions: pressure 1.2MPa, water content range 0-20%, gas phase apparent flow rate 5m/s)

The drawings illustrate the following: 1 inclined inlet, 2 outer pipe wall, 3 helical blade, 4 insulating layer, 5 metal inner electrode, 6 connecting flange and 7 expanding and reducing pipe section

Detailed Description

The present invention will be described in further detail below with reference to the accompanying drawings.

The invention relates to a water content measuring device used in a two-phase flow of moisture, and a schematic structural diagram is shown in figure 1. The device can be matched with any gas flow measuring device for use, such as throttling devices of orifice plates, venturis, nozzles, V cones and the like, and flow meters of ultrasound, turbines, heat type and the like.

The invention is different from the prior moisture content measuring device and is used for measuring the capacitance while carrying out rotational flow phase separation on gas and liquid phases. As shown in figure 1, gas and liquid phases tangentially flow into the rotational flow phase separation section through the inclined inlet 1, in order to realize the resistance-free flow of fluid, the inclined angle of the inlet is 10-50 degrees as same as the lift angle of the helical blade 3, and simultaneously, the cut-in area is ensured to be the same as the flow area of the fluid in the rotational flow phase separation channel, so that the pressure loss is reduced. The liquid phase, due to its high density, moves circularly under the action of centrifugal force and simultaneously passes through the gas phase and is thrown to the pipe wall. Thereby realizing the split-phase flow form that the gas phase is concentrated in the central area and the liquid phase flows along the pipe wall, and overcoming the interference of the inlet flow pattern on the phase content measurement. Simulation research shows that after more than 1 circle of threads, gas-liquid distribution is basically stable and can be used as a measuring section, in the measuring section, a central metal rod is used as an inner electrode 5, a rotational flow phase separator (comprising an insulating layer 4 and helical blades 3) is sleeved on the outer surface of the inner electrode, the outer metal tube wall 2 and a conductive liquid film jointly form an outer electrode, and further a capacitor is formed, and in order to improve the capacitance sensitivity, the diameter ratio of the inner electrode to the outer electrode is 1: 2-1: 10. In the embodiment of fig. 1, the cyclone phase separation section and the measurement section are identical, and the inner electrode penetrates through the whole measurement pipeline, and preferably, another embodiment is provided, wherein the inner electrode is moved downwards and is arranged behind 1 circle of screw pitch from the inclined inlet 1.

The simulation experiment medium is air and water two-phase flow, the working pressure is 1.2MPa, the water content is 15 percent, and the gas phase flow velocity is 10 m/s. As shown in FIG. 2, two straight lines are taken from top to bottom at the positions close to the inner pipe wall and the outer pipe wall on the central section of the rotational flow phase separation section of the invention, which are respectively a near inner wall line and a near outer wall line shown in the figure, and the axial speed, the radial speed and the tangential speed of gas and liquid on the two straight lines are analyzed. At the position close to the inner wall line, the gas-liquid axial speed and the tangential speed both have double speed slip, and for the radial speed, the gas phase is always close to 0, while the liquid phase speed can reach 5m/s, and the direction is directed to the outer pipe wall from the central shaft, which means that the gas at the position close to the inner wall line is kept in the central area and has no tendency of moving towards the outer pipe wall, and the liquid phase passes through the gas phase to diffuse towards the outer pipe wall under the action of strong centrifugal force, thereby realizing the split-phase flow of the gas phase and the; compare in nearly inner wall linear velocity, press close to outer pipe wall department, no matter axial velocity or tangential velocity, the two-phase slip of gas-liquid all is close to 1. The difference is that the gas phase radial velocity is negative, the liquid phase radial velocity is 0, namely, the liquid phase is thrown to the wall surface to form a liquid film without secondary lifting, and the opposite gas phase has the tendency of moving to the central area, thereby realizing the separation of gas phase and liquid phase again. In addition, the distribution rule and the size of the two-phase speed between each thread of the measuring section are basically consistent, namely the gas-liquid two-phase flow in the measuring section is basically stable.

Fig. 3 shows the influence of the liquid phase volume fraction on the liquid phase distribution, the liquid phase is used as a conductive medium and forms an outer electrode of the capacitor together with the metal tube wall, and as the liquid phase volume fraction increases from 5% to 15%, the liquid film on the outer tube wall changes, which means that the corresponding capacitance value also changes obviously. Namely, the capacitance value measured by the invention changes along with the change of the volume fraction of the liquid phase.

FIG. 4 shows the cross-sectional content values corresponding to the positions of the rotational phase separation section under the conditions of pressure of 1.2MPa and speed of 5m/s and different liquid phase volume contents. In the measuring section, the liquid phase section content value is basically kept stable and unchanged, the gas-liquid distribution of the whole measuring section is stable, and the capacitance can be measured.

The graph of the predicted capacitance value and the liquid phase volume fraction under the working conditions of the pressure of 1.2MPA and the flow rate of 5m/s by means of Comsol electric field simulation is shown in a figure 5. As can be seen from the graph, the simulation of the invention predicts that the capacitance value shows the increasing trend along with the increase of the liquid content rate, and can realize that one capacitance value corresponds to a unique liquid phase content value; in addition, the capacitance sensitivity is increased along with the increase of the volume percentage of the liquid phase, under the condition that the liquid percentage is lower than 5%, the capacitance sensitivity is 0.1-0.2 PF, and within the range of 5% -15%, the sensitivity is 0.2-0.3 PF, the liquid percentage is within the range of 15% -20%, and the sensitivity exceeds 0.3 PF.

Claims

1. A vertical rotational flow phase separation capacitance integrated water content measuring device comprises an outer tube wall and an inner electrode, wherein the inner wall of the outer tube wall is a metal inner wall and serves as an outer electrode; the lead angle of the helical blade is between 10 and 50 degrees; at least one pitch is arranged between the uppermost end of the metal inner electrode and the inclined inlet; let the flow path inner diameter be D, the inlet slant length is not shorter than 3D.

2. The moisture content measuring device of claim 1, wherein the helical blade has a total of 2 to 10 turns.

3. The moisture content measuring device of claim 1, wherein the inner diameter of the outer tube wall is 0.3-3D, and the length of the capacitance measuring section is 1-5D.

4. The moisture content measuring device according to any one of claims 1 to 3, wherein the ratio of the diameter of the inner electrode to the diameter of the outer electrode is 1:2 to 1: 10.