Method for improving precision of differential pressure measurement of gas-liquid two-phase flow

Abstract

The application discloses a method for improving the precision of differential pressure measurement of gas-liquid two-phase flow, which is improved on the basis of measuring the differential pressure of gas-liquid two-phase flow by using a differential pressure sensor, and a section of transparent / semi-transparent straight pipe with a scale is added to the pressure lead pipe on any side or both sides of the high-pressure side and the low-pressure side of the differential pressure sensor, and the horizontal height of other pressure lead pipes is kept unchanged. The reading of the differential pressure sensor, the accumulated length of the liquid column in the straight pipe and the inclination of the straight pipe are read, the reading value of the differential pressure sensor is corrected by the differential pressure caused by the liquid column in the straight pipe, and more accurate differential pressure measurement values are obtained. The application can provide an accurate measurement method for the differential pressure measurement of gas-liquid two-phase flow in industrial application and academic research.

Description

Technical Field

[0001] This invention belongs to the field of two-phase flow differential pressure testing technology, specifically relating to a measurement method for improving the accuracy of two-phase flow differential pressure measurement. Background Technology

[0002] Gas-liquid two-phase flow is widely used in phase change heat exchange equipment in energy fields such as power, petroleum, chemical, metallurgy, and HVAC. One of the key performance parameters of these heat exchange equipment is the flow pressure difference between its inlet and outlet. Whether this parameter meets the design requirements depends on obtaining its accurate value. Therefore, accurately obtaining this parameter is one of the important tasks in the field of heat exchangers.

[0003] There are two main conventional methods for measuring pressure difference in two-phase flow. One method uses pressure sensors to measure the pressure at two separate measurement points, and the difference between the pressure sensor readings on the high-pressure side and the low-pressure side is taken as the pressure difference between the two measurement points. The other method uses a pressure difference sensor combined with a pressure tap to directly measure the pressure difference between the two measurement points. These two conventional methods are widely used in engineering applications and academic research. These methods are mostly derived from experience in measuring pressure difference in single-phase flow. However, for more complex fluids such as gas-liquid two-phase flow, these methods have certain limitations.

[0004] For the first conventional method described above, on the one hand, the range of the pressure sensor is selected by the static pressure of the working fluid, which is often several times or even tens of times larger than the pressure difference value; on the other hand, the pressure difference measurement value is obtained by subtracting two pressure values. These two aspects will result in a large measurement error for the pressure difference, and the accuracy is difficult to meet the requirements of engineering and testing. However, its advantage lies in its simple installation, and it has also been used to some extent in engineering and academic research.

[0005] The second conventional method avoids the significant measurement error of the first method, and is therefore more widely used due to this advantage. However, the working fluid at the two pressure measurement points is not always single-phase, and may even be two-phase, and there is often a difference in horizontal height between the measurement points, resulting in liquid columns of varying heights in the pressure taps on both sides of the differential pressure sensor. The pressure difference generated by these liquid columns can introduce considerable deviations into the test results, leading to erroneous measurements if not corrected. Therefore, while the second conventional method may seem to provide more accurate measurements, it actually ignores potential systematic errors, resulting in a measurement error that is difficult to ignore. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and propose a measurement method to improve the accuracy of two-phase flow differential pressure measurement.

[0007] To achieve the objectives of this invention, a technical solution is proposed: a method for improving the accuracy of differential pressure measurement in gas-liquid two-phase flow, comprising a differential pressure sensor connected between a high-pressure measuring point and a low-pressure measuring point in a two-phase flow channel via a pressure-sensing tube; a section of graduated transparent / semi-transparent straight tube is added to the pressure-sensing tube on either side of the high-pressure side or both sides of the differential pressure sensor, the pressure-sensing tubes on both sides of the differential pressure sensor are kept at the same horizontal height, and the pressure-sensing tube connected to a certain measuring point is kept at the same horizontal height as that measuring point.

[0008] This technical solution can be implemented under three different operating conditions.

[0009] For operating condition 1, a differential pressure sensor is used in conjunction with two graduated transparent / semi-transparent straight tubes to measure the pressure difference of two-phase flow through a certain channel. The pressure tapping tube on the high-pressure side of the differential pressure sensor is divided into three sections: one section serves as the second high-pressure tapping tube connected to the differential pressure sensor, another section serves as the first high-pressure tapping tube connected to the high-pressure measuring point, and the middle section is a graduated transparent / semi-transparent straight tube on the high-pressure side. Similarly, the pressure tapping tube on the low-pressure side of the differential pressure sensor is divided into three sections: one section serves as the second low-pressure tapping tube connected to the differential pressure sensor, another section serves as the first low-pressure tapping tube connected to the low-pressure measuring point, and the middle section is a graduated transparent / semi-transparent straight tube on the low-pressure side. The second high-pressure tapping tube and the second low-pressure tapping tube are at the same horizontal height; the first high-pressure tapping tube and the high-pressure measuring point are at the same horizontal height; and the first low-pressure tapping tube and the low-pressure measuring point are at the same horizontal height.

[0010] For operating condition 2, a differential pressure sensor is used in conjunction with a graduated transparent / semi-transparent straight tube to measure the pressure difference when two-phase flow passes through a certain channel. The pressure tapping tube on the high-pressure side of the differential pressure sensor is divided into three sections: one section serves as the second high-pressure tapping tube connected to the differential pressure sensor, another section serves as the first high-pressure tapping tube connected to the high-pressure measuring point, and the middle section is a graduated transparent / semi-transparent straight tube on the high-pressure side. The low-pressure tapping tube is kept at the same horizontal height as the low-pressure measuring point; the second high-pressure tapping tube is kept at the same horizontal height as the low-pressure tapping tube; and the first high-pressure tapping tube is kept at the same horizontal height as the high-pressure measuring point.

[0011] For operating condition 3, a differential pressure sensor is used in conjunction with a graduated transparent / semi-transparent straight tube to measure the pressure difference when two-phase flow passes through a certain channel. The pressure tap on the low-pressure side of the differential pressure sensor is divided into three sections: one section serves as the second low-pressure tap connected to the differential pressure sensor, another section serves as the first low-pressure tap connected to the low-pressure measuring point, and the middle section is a graduated transparent / semi-transparent straight tube on the low-pressure side. The high-pressure side tap is at the same horizontal level as the high-pressure measuring point; the second low-pressure tap is at the same horizontal level as the high-pressure side tap; and the first low-pressure tap is at the same horizontal level as the low-pressure measuring point.

[0012] The two-phase flow differential pressure testing system used in this invention mainly consists of a two-phase flow channel, a high-pressure two-phase flow, a low-pressure two-phase flow, a high-pressure measuring point, a first high-pressure tapping tube, a graduated transparent / semi-transparent straight tube, a second high-pressure tapping tube, a differential pressure sensor, a first low-pressure tapping tube, a second low-pressure tapping point, a low-pressure measuring point, a high-pressure side tapping tube, and a low-pressure side tapping tube; the connections between each point are good, and the system has good airtightness.

[0013] Furthermore, the present invention provides the following measurement scheme, which corrects the reading of the differential pressure sensor by using the pressure difference brought by the liquid column in the straight tube, making the measurement more accurate: the graduated transparent tube can be installed horizontally, vertically, or at an angle; for operating conditions 1 and 2, when the horizontal height of the second high-pressure tapping tube is higher than that of the first high-pressure tapping tube, the tilt angle of the graduated transparent / semi-transparent straight tube on the high-pressure side is positive, 90° when vertical, and 0° when horizontal, and vice versa; for operating conditions 1 and 3, when the horizontal height of the second low-pressure tapping tube is higher than that of the first low-pressure tapping tube, the tilt angle of the graduated transparent / semi-transparent straight tube on the low-pressure side is positive, 90° when vertical, and 0° when horizontal, and vice versa; the reading of the differential pressure sensor is ΔP. read The cumulative height of the liquid column in the graduated transparent / semi-transparent straight tube on the high-pressure side is ΔH, and the tilt angle is α. The cumulative height of the liquid column in the graduated transparent / semi-transparent straight tube on the low-pressure side is ΔHT, and the tilt angle is β.

[0014] The data processing procedure is as follows:

[0015] For operating condition 1, the actual measured differential pressure ΔP real It should be: ΔP real =ΔP read +ρgΔHsinα-ρgΔHTsinβ

[0016] For operating condition 2, the actual measured differential pressure ΔP real It should be: ΔP real =ΔP read +ρgΔHsinα

[0017] For operating condition 3, the actual measured differential pressure ΔP real It should be: ΔP real =ΔP read -ρgΔHTsinβ

[0018] In the formula, ρ is the density of the liquid inside the pipe, which is obtained by looking up the physical property parameter table from the saturation pressure inside the pipe;

[0019] In the formula, g is the local gravitational acceleration.

[0020] Furthermore, the flow regime at both the high-pressure and low-pressure measuring points can be any flow regime among the gas phase, liquid phase, and gas-liquid two-phase flow regimes.

[0021] The above methods for reading the height of the liquid column in a transparent / semi-transparent straight tube can be achieved visually or by using other technical means.

[0022] Compared with the prior art, the present invention has the following advantages: it not only avoids the large measurement error caused by subtracting the absolute pressure value from the first measurement of the pressure difference, but also corrects the systematic error in the direct measurement of the pressure difference, which can greatly improve the measurement accuracy of the two-phase flow pressure difference. The method is simple and easy to implement, and has strong feasibility. In practice, it has a good effect on reducing engineering redundancy and discovering scientific problems. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of working condition 1 in the test method described in this invention;

[0024] Figure 2 This is a schematic diagram of working condition 2 in the test method described in this invention;

[0025] Figure 3 This is a schematic diagram of working condition 3 in the test method described in this invention;

[0026] In the diagram: 1-Two-phase flow channel, 2-High-pressure two-phase flow, 3-Low-pressure two-phase flow, 4-High-pressure measuring point, 5-First high-pressure tap, 6-High-pressure side graduated transparent / semi-transparent straight tube, 7-Second high-pressure tap, 8-Differential pressure sensor, 9-Second low-pressure tap, 10-Low-pressure side graduated transparent / semi-transparent straight tube, 11-First low-pressure tap, 12-Low-pressure measuring point, 13-Low-pressure side tap, 14-High-pressure side tap;

[0027] Figure 4 This is an example diagram comparing the measurement errors of the two-phase flow pressure difference between the method of the present invention and the conventional method;

[0028] Figure 4 In the diagram: the horizontal axis represents the possible differences in liquid column height, and the vertical axis represents the measurement errors of different methods under a specific example operating condition. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings.

[0030] like Figure 1 , 2 As shown in Figure 3, the present invention is a method for improving the measurement accuracy of pressure difference in gas-liquid two-phase flow. The principle of this method is to obtain the pressure difference caused by the cumulative length of the liquid column in the straight pipe, so as to correct the reading value of the pressure difference sensor.

[0031] During the implementation of the method, depending on the different operating conditions 1, 2, and 3, it is necessary to read the differential pressure sensor reading ΔP. readThe data includes any one or two sets of data, such as the cumulative height ΔH and tilt angle α of the liquid column in the high-pressure side with graduations in the transparent / semi-transparent straight pipe, and the cumulative height ΔHT and tilt angle β of the liquid column in the low-pressure side with graduations in the transparent / semi-transparent straight pipe.

[0032] For operating conditions 1 and 2, when the horizontal height of the second high-pressure tap is higher than that of the first high-pressure tap, the tilt angle of the graduated transparent / semi-transparent straight tube on the high-pressure side is positive, 90° when vertical and 0° when horizontal, and negative otherwise; for operating conditions 1 and 3, when the horizontal height of the second low-pressure tap is higher than that of the first low-pressure tap, the tilt angle of the graduated transparent / semi-transparent straight tube on the low-pressure side is positive, 90° when vertical and 0° when horizontal, and negative otherwise.

[0033] The data processing procedure is as follows:

[0034] For operating condition 1, the actual measured differential pressure ΔP real It should be: ΔP real =ΔP read +ρgΔHsinα-ρgΔHTsinβ

[0035] For operating condition 2, the actual measured differential pressure ΔP real It should be: ΔP real =ΔP read +ρgΔHsinα

[0036] For operating condition 3, the actual measured differential pressure ΔP real It should be: ΔP real =ΔP read -ρgΔHTsinβ

[0037] In the formula, ρ is the density of the liquid inside the pipe, which is obtained by looking up the physical property parameter table from the saturation pressure inside the pipe;

[0038] In the formula, g is the local gravitational acceleration.

[0039] The advantages of the present invention will be illustrated below with an example;

[0040] Taking the two-phase flow pressure difference of R134a at 6℃ as an example, the saturation pressure is 0.36198MPa. Assuming the actual pressure difference is 15-55kPa, conventional method 1 uses two pressure sensors with an accuracy of 0.1 and a pressure range of 0-0.7MPa. Conventional method 2 uses a pressure difference sensor with an accuracy of 0.1 and a pressure range of 0-60kPa. The invention method is implemented according to the scheme of working condition 1, and the minimum scale of the straight pipe used is 1mm.

[0041] When the horizontal height difference at the measurement point varies from 5mm to 1200mm, the possible range of variation in the liquid column height difference is the same.

[0042] The error of conventional method 1 is ±1.80% to ±6.60%, and the error increases as the differential pressure measurement value decreases;

[0043] The error range of conventional method 2 is ±0.16% to ±100.0%. The error increases with the increase of the liquid column height difference and with the decrease of the pressure difference measurement value.

[0044] The error range of the method of the present invention under working condition 1 is ±0.11% to ±0.4%, which is negligible compared with the error changes of working conditions 2 and 3, and the error increases as the differential pressure measurement value decreases;

[0045] The error after using the method of the present invention is 1 / 16 of the error of conventional method 1, and 1 / 1.4 to 1 / 248 of the error of conventional method 2, with most of them being between 1 / 10 and 1 / 248.

[0046] The higher the saturation pressure of the working fluid, the higher the error of conventional method 1. However, it has no effect on the error of the method of the present invention, that is, the advantages of the method of the present invention will be more obvious.

[0047] The greater the horizontal height difference of the measurement points, the greater the height difference of the liquid column may be, and the higher the error of conventional method 2. However, the error of the method of the present invention can be ignored, that is, the advantages of the method of the present invention will be more obvious.

[0048] It should be understood that the embodiments and examples discussed herein are merely illustrative and may be modified or altered by those skilled in the art, and all such modifications and alterations should fall within the scope of protection of the appended claims.

Claims

1. A method for improving the accuracy of differential pressure measurement in a gas-liquid two-phase flow, comprising a differential pressure sensor (8) connected via a pressure tap between a high-pressure measuring point (4) and a low-pressure measuring point (12) in a two-phase flow channel; characterized in that, A section of transparent / semi-transparent straight tube with scale is added to the pressure tapping tubes on the high-pressure side and low-pressure side of the differential pressure sensor (8). The pressure tapping tubes on both sides of the differential pressure sensor (8) are kept at the same horizontal height. The pressure tapping tube connected to a certain pressure measuring point is kept at the same horizontal height as the pressure measuring point. The pressure difference of two-phase flow passing through a certain channel is measured using a differential pressure sensor (8) combined with two graduated transparent / semi-transparent straight tubes. The pressure tapping tube on the high-pressure side of the differential pressure sensor (8) is divided into three sections: one section serves as the second high-pressure tapping tube (7) connected to the differential pressure sensor (8), another section serves as the first high-pressure tapping tube (5) connected to the high-pressure measuring point (4), and the middle section is a graduated transparent / semi-transparent straight tube (6) on the high-pressure side. Similarly, the pressure tapping tube on the low-pressure side of the differential pressure sensor (8) is divided into three sections: one section serves as the second low-pressure tapping tube (9) connected to the differential pressure sensor (8), another section serves as the first low-pressure tapping tube (11) connected to the low-pressure measuring point (12), and the middle section is a graduated transparent / semi-transparent straight tube (10) on the low-pressure side. The second high-pressure tapping tube (7) and the second low-pressure tapping tube (9) ) Maintain the same horizontal height; the first high-pressure tap (5) and the high-pressure measuring point (4) maintain the same horizontal height; the first low-pressure tap (11) and the low-pressure measuring point (12) maintain the same horizontal height; the high-pressure and low-pressure side graduated transparent / semi-transparent straight tubes can be installed horizontally, vertically or tilted; when the horizontal height of the second high-pressure tap (7) is higher than that of the first high-pressure tap (5), the tilt angle of the high-pressure side graduated transparent / semi-transparent straight tube (6) is positive, 90° when vertical, 0° when horizontal, and negative otherwise; when the horizontal height of the second low-pressure tap (9) is higher than that of the first low-pressure tap (11), the tilt angle of the low-pressure side graduated transparent / semi-transparent straight tube (10) is positive, 90° when vertical, 0° when horizontal, and negative otherwise; the reading of the differential pressure sensor (8) is Δ P read The cumulative height of the liquid column inside the graduated transparent / semi-transparent straight tube (6) on the high-pressure side is Δ H Inclination angle is α The cumulative height of the liquid column inside the graduated transparent / semi-transparent straight tube (10) on the low-pressure side is Δ HT Inclination angle is β ; The data processing procedure is as follows: Actual differential pressure measurement Δ P real It should be: Δ P real =Δ P read + ρg Δ H sin α - ρg Δ HT sin β In the formula ρ It is the density of the liquid inside the pipe, which is obtained by looking up the physical property parameter table from the saturation pressure inside the pipe; In the formula g This is the local gravitational acceleration.

2. A method for improving the accuracy of differential pressure measurement in a gas-liquid two-phase flow, comprising a differential pressure sensor (8) connected via a pressure tap between a high-pressure measuring point (4) and a low-pressure measuring point (12) in a two-phase flow channel; characterized in that, A section of transparent / semi-transparent straight tube with scale is added to the pressure tapping tube on the high-pressure side of the differential pressure sensor (8). The pressure tapping tubes on both sides of the differential pressure sensor (8) are kept at the same horizontal height. The pressure tapping tube connected to a certain pressure measuring point is kept at the same horizontal height as the pressure measuring point. The pressure difference of two-phase flow passing through a certain channel is measured using a differential pressure sensor (8) combined with a graduated transparent / semi-transparent straight tube. The high-pressure side pressure tap of the differential pressure sensor (8) is divided into three sections. One section serves as the second high-pressure tap (7) connected to the differential pressure sensor (8), another section serves as the first high-pressure tap (5) connected to the high-pressure measuring point (4), and the middle section is a graduated transparent / semi-transparent straight tube (6) on the high-pressure side. The low-pressure side pressure tap (13) is at the same horizontal level as the low-pressure measuring point (12); the second high-pressure tap (7) is at the same horizontal level as the low-pressure side pressure tap (13); and the first high-pressure tap (5) is at the same horizontal level as the high-pressure measuring point (4). The high-pressure side graduated transparent / semi-transparent straight tube (6) can be installed horizontally, vertically, or at an angle; when the horizontal height of the second high-pressure tap (7) is higher than that of the first high-pressure tap (5), the tilt angle of the high-pressure side graduated transparent / semi-transparent straight tube (6) is positive, 90° when vertical, and 0° when horizontal, and negative otherwise; the reading of the differential pressure sensor (8) is Δ P read The cumulative height of the liquid column inside the graduated transparent / semi-transparent straight tube (6) on the high-pressure side is Δ H Inclination angle is α , The data processing procedure is as follows: Actual differential pressure measurement Δ P real It should be: Δ P real =Δ P read + ρg Δ H sin α In the formula ρ It is the density of the liquid inside the pipe, which is obtained by looking up the physical property parameter table from the saturation pressure inside the pipe; In the formula g This is the local gravitational acceleration.

3. A method for improving the accuracy of differential pressure measurement in a gas-liquid two-phase flow, comprising a differential pressure sensor (8) connected via a pressure tap between a high-pressure measuring point (4) and a low-pressure measuring point (12) in a two-phase flow channel; characterized in that, A section of transparent / semi-transparent straight tube with scale is added to the pressure tapping tube on the low-pressure side of the differential pressure sensor (8). The pressure tapping tubes on both sides of the differential pressure sensor (8) are kept at the same horizontal height. The pressure tapping tube connected to a certain pressure measuring point is kept at the same horizontal height as the pressure measuring point. The pressure difference of two-phase flow passing through a certain channel is measured by using a differential pressure sensor (8) in conjunction with a graduated transparent / semi-transparent straight tube. The low-pressure side pressure tap of the differential pressure sensor (8) is divided into three sections. One section serves as the second low-pressure tap (9) connected to the differential pressure sensor (8), another section serves as the first low-pressure tap (11) connected to the low-pressure measuring point (12), and the middle section is a graduated transparent / semi-transparent straight tube (10) on the low-pressure side. The high-pressure side pressure tap (14) is at the same horizontal level as the high-pressure measuring point (4); the second low-pressure tap (9) is at the same horizontal level as the high-pressure side pressure tap (14); and the first low-pressure tap (11) is at the same horizontal level as the low-pressure measuring point (12). The graduated transparent / semi-transparent straight tube (10) on the low-pressure side can be installed horizontally, vertically, or at an angle; when the horizontal height of the second low-pressure tap (9) is higher than that of the first low-pressure tap (11), the tilt angle of the graduated transparent / semi-transparent straight tube (10) on the low-pressure side is positive, 90° when vertical, and 0° when horizontal, and negative otherwise; the reading of the differential pressure sensor (8) is Δ P read The cumulative height of the liquid column inside the graduated transparent / semi-transparent straight tube (10) on the low-pressure side is Δ HT Inclination angle is β ; The data processing procedure is as follows: Actual differential pressure measurement Δ P real It should be: Δ P real =Δ P read - ρg Δ HT sin β In the formula ρ It is the density of the liquid inside the pipe, which is obtained by looking up the physical property parameter table from the saturation pressure inside the pipe; In the formula g This is the local gravitational acceleration.

4. A method for improving the accuracy of pressure difference measurement in gas-liquid two-phase flow according to any one of claims 1-3, characterized in that, The flow state at the high pressure measuring point (4) and the low pressure measuring point (12) can be any flow state among gas phase, liquid phase and gas-liquid two phases.

5. A method for improving the accuracy of pressure difference measurement in gas-liquid two-phase flow according to any one of claims 1-3, characterized in that, The method for reading the height of the liquid column in a graduated transparent / semi-transparent straight tube is by visual inspection.

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