CN107044820A - The direct measurement system of annular flow local dynamic station liquid film average thickness - Google Patents

Abstract

The invention relates to a direct measurement system for the average thickness of the local dynamic liquid film in an annular flow, which is used to measure the liquid film of the conductive liquid flowing in the pipeline. A needle sensor and a precision resistance; a contact probe sensor with adjustable insertion depth, including a spiral micrometer 6, a double parallel contact probe 2, a connecting part 9, a fixed support 3, a retractable support 7 and a spring 8.

Description

A Direct Measuring System of Local Dynamic Liquid Film Average Thickness in Annular Flow

technical field

The invention relates to a measuring system for the average thickness of the local dynamic liquid film in an annular flow.

Background technique

Multiphase flow processes widely exist in many departments and industrial processes such as petroleum, chemical industry, metallurgy, water supply, medicine, and environmental engineering. It is an important research field that is widely concerned at home and abroad. A multiphase flow system usually consists of two continuous media and several discontinuous media. Different multiphase flows including the number of material phases in root excavation fluids can generally be divided into two-phase and three-phase flows. According to the different physical states of the components, two-phase flow is generally divided into gas/liquid, gas/solid, liquid/solid, liquid/liquid (such as oil/water) two-phase flow; three-phase flow is generally divided into gas/liquid/ Liquid, gas/liquid/solid three-phase flow, etc. The thickness of the liquid film existing in the gas-liquid interface of multiphase flow not only has a great influence on the heat transfer, mass transfer and resistance characteristics of gas-liquid two-phase flow, but also is the basis for calculating multiphase fluid dynamics, so the correct and effective The measurement of liquid film thickness is the key to understanding these properties. So far, there are mainly the following five liquid film measurement methods: (1) conductometric method; (2) capacitance method; (3) optical method; (4) acoustic wave method (5) nuclear radiation method. The basic principle of the conductivity method is that there is a certain correspondence between the height of the liquid film and its conductance, and the thickness of the liquid film can be obtained by measuring the conductance. This method is limited to conductive liquids. The main principle of the capacitance method is that the gas-liquid two-phase has different dielectric constants, and the thickness change of the liquid phase between the two electrodes is reflected by the capacitance change between the two electrodes, but the capacitance method is affected by the gas-liquid two-phase flow pattern and temperature change Larger for square pipes. The optical method is one of the methods with high measurement accuracy. Among them, the interface detection method, laser scattering method and fluorescence intensity method generally need to add dyes, latex particles or fluorescent agents in the liquid phase. The accuracy of the added mass concentration, The change of excitation light intensity and time and space are directly related to the measurement uncertainty of liquid film thickness, its uniformity in the liquid phase cannot be guaranteed, and it is a consumable item, which is only suitable for laboratory measurement, which limits its popularization and application; The light and shadow method measures the thickness of the liquid film by recording the shadow formed by the reflection and refraction of the liquid film by the camera. This method has poor real-time performance and cannot respond quickly to changes in the liquid film; the laser focus displacement method and interferometry are very effective for measuring the thickness of thin liquid films. , high resolution, but the structure of the two measurement systems is complex and requires high sensor performance. Due to the use of transparent pipes, its use in the measurement of medium and high pressure liquid film thickness is limited; among the light attenuation methods, the visible light attenuation method is only suitable for For translucent media that absorb visible light, the mid-infrared attenuation method is only suitable for the measurement of extremely thin liquid films of 2-30 μm due to its strong absorption. Acoustic method is based on ultrasonic technology, which has a powerful function of describing flow pattern characteristics. It uses the principle of attenuation and reflection when passing through discontinuous media to measure the thickness of liquid film, but it cannot measure wavy liquid film, which will cause ultrasonic detection after reflection. difficulty. The disadvantage of the nuclear radiation method is that it is highly radioactive, and requires necessary heavy safety protection when used, which limits its application in industrial sites.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art, and provide a method for directly measuring the average thickness of the local dynamic liquid film in annular flow.

To achieve the above object, the present invention takes the following technical solutions:

A direct measurement system for the average thickness of the local dynamic liquid film of annular flow, which is used to measure the liquid film of the conductive liquid flowing in the pipeline. The measurement system used includes a data measurement module, a data acquisition module and a data processing module, wherein, The data measurement module includes a DC stabilized power supply, a contact probe sensor with adjustable insertion depth and a precision resistor;

The contact probe sensor with adjustable insertion depth includes a spiral micrometer 6, a double parallel contact probe 2, a connecting part 9, a fixed support 3, a telescopic support 7 and a spring 8, wherein the spiral micrometer 6 The main body is fixed on the fixed bracket 3; the connecting part 9 includes a shell 10, which is fixedly connected to the support ring on the shell 10, and the metal rod 13 is closely attached to the inner side of the support ring 12; the measuring end of the screw micrometer 6 and the metal of the connecting part 9 The rods 13 are connected; the double parallel contact probes 2 are fixed on the lower part of the connecting part 9 shell; Between the bracket and the connecting part 9; the double parallel contact probes 2 are coated with hydrophobic materials except the lower end of the probes; the stabilized voltage source provided by the DC power supply is loaded on the precision resistors connected in series and the double parallel contact probes 2, The voltage at both ends of the precision resistor is collected by the data acquisition module and sent to the data processing module.

As a preferred embodiment, the support ring includes an outer metal ring 11 connected to each other and a rubber ring 12 inside the outer metal ring 11 .

The present invention has the following advantages due to the adoption of the above technical scheme:

(1) The stabilized voltage source is provided by the DC stabilized power supply module, which is connected in series with a precision resistor and a contact probe sensor with adjustable insertion depth. The data acquisition module is used to collect the voltage at both ends of the precision resistor. The corresponding voltage signal obtained from the insertion depth realizes the direct measurement of the thickness of the liquid film.

(2) According to the different precision requirements, the insertion depth increment value of the probe sensor is selected, that is, different numbers of liquid film thicknesses can be obtained, which can meet the measurement under different precision requirements.

(3) Due to the special design of the contact probe structure with adjustable insertion depth, the special function that the spiral micrometer rotates but the contact probe connected to it does not rotate is realized, which effectively solves the problem of wire winding.

Description of drawings

Figure 1 shows a contact probe sensor with adjustable insertion depth

Figure 2 is a structural diagram of the contact probe sensor connection parts with adjustable insertion depth

Figure 3 is a schematic diagram of the optimized weighted average thickness algorithm

Figure 4 is the specific structural connection diagram of the direct measurement system for the local dynamic liquid film average thickness of the annular flow

Figure 5 is the measurement circuit connection diagram

Figure 6 is a flow chart of the measurement method

Explanation of symbols in the figure: 1 pipeline; 2 double parallel contact probes; 3 fixed bracket; 4 fixed screw; 5 lead wire; 6 spiral micrometer; 7 telescopic support; 8 spring; 11 metal ring outer ring; 12 rubber ring; 13 metal rod

detailed description

The system includes data measurement module, data acquisition module and data processing module. Among them, the data measurement module includes a DC power supply, a contact probe sensor with adjustable insertion depth, and a precision resistor; the data acquisition module includes a data acquisition card, a computer and data acquisition software; the data processing module includes a computer and implements a weighted average thickness algorithm software. The device provides a stabilized voltage source through a DC stabilized power supply module, which is connected in series with a precision resistor and a contact probe sensor with adjustable insertion depth. The data acquisition module is used to collect the voltage at both ends of the precision resistor. When the conductive liquid submerges the probe probe, The two probes are connected, and the entire circuit forms a loop. The current flows through the precision resistor, and the voltage at both ends is not zero. When there is no liquid between the two probes, the voltage at both ends of the precision resistor is zero. During continuous measurement, It is represented by different duty ratios. According to different precision requirements, the insertion depth increment value of the probe sensor is selected to obtain the voltage signal corresponding to the insertion depth. Finally, the data processing module uses the weighted average thickness algorithm to calculate the local dynamic liquid film. The average thickness.

In order to directly measure the average thickness of the local dynamic liquid film in the annular flow, a pair of double parallel contact probes are inserted into the tube, so that the probes are located near the liquid film, and the upper end is connected with the screw micrometer fixed on the tube wall , its leads are connected with precision resistors and DC stabilized voltage power supply. When the probe head is in contact with the liquid on the surface of the liquid film, a conductive path is formed between the probe heads; When in contact, the circuit is open. Whether the liquid film is in contact with the probe head can be judged by measuring the voltage across the precision resistance in the circuit thus formed. Adjust the screw micrometer to make the insertion depth of the contact probe gradually increase. When a non-zero signal begins to appear in the collected data, record the insertion depth value and its corresponding voltage signal time series at this time; The incremental value of the insertion depth of the needle sensor, continue to adjust the screw micrometer downward, and record each insertion depth value and its corresponding voltage signal time series in turn, until the detected voltage signal remains a non-zero voltage. Convert the insertion depth value into the liquid film thickness value, convert the voltage signal time series into the duty cycle corresponding to the insertion depth value, and sort the duty cycle from small to large to get the value corresponding to each liquid film thickness value. Assuming that the liquid film thickness sequence is hi(i=1,2,3,...,N), the corresponding weight sequence is wi(i=1,2,3,...,N), so the average Liquid film thickness H=(h1×w1+h2×w2+h3×w3+…+hN×wN).

In order to realize the function of the contact probe with adjustable insertion depth, the structural design is as follows: including the spiral micrometer 6, the double parallel contact probe 2, the connecting part 9, the fixed bracket 3, the telescopic bracket 7, the spring 8 and the lead wire 5 , and its connecting parts include a plexiglass casing 10, a metal ring outer ring 11, a rubber ring 12, and a metal rod 13. The double-parallel contact probe 2 is coated with hydrophobic material except for the front end of the probe 1mm, so as to eliminate the measurement error caused by surface tension. The plexiglass casing 10 in the connecting part 9, the metal ring outer ring 11, and the rubber ring 12 are bonded with superglue, and the metal rod 13 is placed in the center, and its upper end is closely attached to the inner side of the rubber ring 12, and its lower end is lower than the rubber ring 12. The ends are tightly fitted to achieve free rotation but fixed up and down. Renovate the spiral micrometer 6, connect its lower end with the metal rod 13 of the connecting part 9, install double parallel contact probes 2 at the lower end of the connecting part 9, install the above whole on the pipeline through the fixing bracket 3, and then pass The telescopic bracket 7 connects the connection part 9 with the fixed bracket 3, and its telescopic bracket 7 is a hollow tube, and the two electrodes of the double-parallel contact probe 2 are drawn out through the telescopic bracket 7, and outside the telescopic bracket 7 is a A spring 8 increases the stress of the double-parallel contact probe 2 and the spiral micrometer 6, and reduces the measurement error caused by the impact of the water flow on the double-parallel contact probe 2.

Connect the experimental pipe section with a contact probe with adjustable insertion depth to the two-phase flow system, see Figure 4, and connect it in series with a precision resistor and a DC stabilized voltage power supply, see Figure 5. Adjust the flow rate of gas phase and liquid phase to form an annular flow in the experimental pipe section and keep it stable. Adjust the screw micrometer to make the insertion depth of the contact probe slowly increase. When a non-zero signal begins to appear in the collected data, record the depth value at this time and the corresponding voltage signal time series; according to the different accuracy requirements, select Determine the incremental value of the insertion depth of the probe sensor, continue to adjust the screw micrometer downward, and collect the time series of voltage signals for each insertion depth value. Import the data collected by the acquisition software into an Excel table, convert the sequence of inserted depth values into a sequence of liquid film thickness, and convert the time series of voltage signals into a duty cycle, and proceed according to the liquid film thickness from high to low in the Excel table Sort. Check whether the duty cycle in the sorted data is sorted from low to high. If so, the collected data can be used to calculate the average thickness of the dynamic liquid film. If not, it means that the flow pattern has not reached a steady state when the data is collected and needs to be measured again.

Take the case of collecting 5 insertion depth values as an example, as shown in Figure 3, assuming that the sampling range is within the dashed box, where the duty cycle corresponding to h1 is t1/t, the duty cycle corresponding to h2 is t2/t, and the duty cycle corresponding to h3 is The duty cycle is t3/t, the duty cycle corresponding to h4 is t4/t, the duty cycle corresponding to h5 is t5/t, the area of the red diagonal line is the product of h1 and t1, and the area of the green square is h2 and (t2- t1), the area of the purple mesh is the product of h3 and (t3-t1), the area of the blue horizontal line is the product of h4 and (t4-t3), the area of the yellow vertical line is the product of h5 and (t5-t4) , and the product of the average thickness h and t is approximately the sum of the above areas, so the average thickness h=(h1×t1+h2×(t2-t1)+h3×(t3-t1)+h4×(t4-t3)+ h5×(t5-t4))/t.

Claims (2)

1. a kind of direct measurement system of annular flow local dynamic station liquid film average thickness, the conduction flowed for measuring in pipeline The liquid film of liquid, including data measurement module, data acquisition module and data processing module, wherein, data measurement module bag Include the adjustable contact probe sensor of D.C. regulated power supply, insertion depth and a precision resistance；

The adjustable contact probe sensor of described insertion depth, including micrometer caliper (6), double parallel contact probe (2), company Relay part (9), fixed support (3), telescoping shoring column (7) and spring (8), wherein, the main body of micrometer caliper (6) is fixed on On fixed rack (3)；Connection member (9) includes shell (10), is fixedly connected on support ring on shell (10), metallic rod (13) and branch It is close on the inside of pushing out ring (12)；The measurement end of micrometer caliper (6) is connected with the metallic rod (13) of connection member (9)；Double parallel connects Feeler inspection pin (2) is fixed on the bottom of connection member (9) shell；Connection member (9) passes through telescoping shoring column (7) and fixed support (3) it is connected, spring is provided with outside the montant of telescoping shoring column (7), spring is placed between fixed support and connection member (9)； Double parallel contact probe (2) coats hydrophobic material in addition to probe lower end；The source of stable pressure that D.C. regulated power supply is provided is carried in phase On the precision resistance and double parallel contact probe (2) mutually connected, the voltage at precision resistance two ends is after data collecting module collected It is admitted to data processing module.

2. direct measuring method according to claim 1, it is characterised in that described support ring includes the gold being connected with each other Belong to ring outer ring (11) and the rubber ring (12) in becket outer ring (11).