A concave arc dual-flow direction average velocity tube flowmeter

Abstract

The present invention relates to a concave arc dual-flow average velocity tube flowmeter, including a detection rod inserted into a measuring pipeline along a diameter, a total pressure tube and a static pressure tube arranged in the detection rod, the total pressure tube is located on the upstream surface, the static pressure tube is located on the back surface, and a total pressure hole and a static pressure hole are arranged on the upstream surface and the back surface of the detection rod, all the total pressure holes are connected with the total pressure tube, and the average total pressure p is drawn from the total pressure tube; all the static pressure holes are connected with the static pressure tube, and the static pressure p is drawn from the static pressure tube; the difference between the measured total pressure p and the static pressure p is used to obtain the size of the average flow velocity on the pipeline cross section, characterized in that the cross-sectional shape of the detection rod is similar to a rhombus, and the four sides are all concave arcs, the upstream surface and the back surface are both convex arcs, and the concave arc edges are streamlined. The present invention can effectively improve the output differential pressure of the average velocity tube flowmeter and improve the accuracy of the low flow measurement of the average velocity tube.

Description

Technical Field

[0001] The invention relates to an average velocity tube flowmeter. Background Art

[0002] As one of the insertion flow meters, the average velocity tube flowmeter (known as Annubar, Verabar, Probar, etc. abroad) is a differential pressure flowmeter developed in the late 1960s based on the principle of pitot tube velocity measurement. Compared with traditional flow sensors, the average velocity tube flowmeter is widely used in the flow measurement of large-diameter pipelines in the power, metallurgy, petrochemical and other industries due to its simple structure, easy installation and disassembly, small pressure loss and low cost. It has the following advantages:

[0003] (1) Wide range of applications. Average velocity tube flowmeters can be used to measure the flow of all fluids that do not contain solid particles; they are applicable to a wide range of pipe diameters, with a minimum diameter of 25 mm and a maximum diameter of 9 m; they can measure the flow of irregular pipes (such as square or rectangular pipes).

[0004] (2) The average velocity tube flowmeter has a simple structure, light weight, and is easy to install, disassemble, and maintain. It can be disassembled and assembled without interrupting flow, and has a low manufacturing cost.

[0005] (3) Small pressure loss and energy saving. The irrecoverable pressure loss of the average velocity tube flowmeter only accounts for 2-15% of its output differential pressure, which is less than 5% of the orifice plate, significantly reducing power consumption and achieving significant energy saving effects.

[0006] (4) Good long-term stability of accuracy. The average velocity tube flowmeter has no moving or easily worn parts. When the tube diameter is greater than 300mm, its accuracy can reach ±1% and its stability is ±0.1%, which generally meets practical requirements.

[0007] The average velocity tube flowmeter is an insertion differential pressure flow sensor. The diameter of the circumscribed circle of the cross section of its detection rod is much smaller than the diameter of the pipe cross section, resulting in a small output differential pressure. It is also easily affected by the vortex downstream of the detection rod and fluctuates, making it difficult to improve the linearity and repeatability of the average velocity tube. Therefore, since the advent of the average velocity tube flowmeter, researchers have been committed to the study of its cross-sectional shape to increase the output differential pressure of the average velocity tube flowmeter and improve its linearity, repeatability and other performance indicators. At present, there are four most widely used average velocity tube cross-sectional shapes: circular, diamond, Delta and bullet-shaped.

[0008] (a) Circular: The earliest cross-sectional shape of the velocity-averaging tube detection rod. Later, it was found that the flow rate was less than Reynolds number Re10 5 When Re>10 6 When Re is 10 5 ~10 6When the separation point is uncertain, the flow coefficient has a deviation of nearly ±10%.

[0009] (b) Diamond: Introduced by DSI in the United States in 1978, the cross section of the detection rod has sharp edges. When the fluid flows around them, the separation point is fixed on the sharp edges. It mainly solves the problem of fluid separation point variation in circular average velocity tube flowmeters and can obtain higher differential pressure, but its repeatability is not very ideal.

[0010] (c) Delta shape, launched by Cisco in Germany, has performance similar to that of the diamond-shaped averaging tube. While the separation point is fixed, the averaging tube itself has a significant impact on the flow field. A vortex with large movement intensity and scale appears in its downstream area. Under its influence, the differential pressure of the averaging tube fluctuates greatly, the repeatability is affected, and the linearity is difficult to improve.

[0011] (d) Bullet-shaped, launched by Veris in the United States in 1992, called Verbar. Verbar has a rough surface on the front end of its bullet to improve its measurement accuracy. The bullet shape adopts a streamlined cross-sectional shape, which reduces the impact of the velocity averaging tube on the flow field and improves linearity. However, the position of the static pressure point makes its output differential pressure much lower than that of other types of velocity averaging tubes, affecting its measurement effect under low density and low flow rate conditions. Summary of the invention

[0012] The purpose of the present invention is to provide a new cross-sectional shape of an average velocity tube, named as a concave arc dual-flow average velocity tube flowmeter, based on the interaction between the cross-sectional shape of the average velocity tube and the flow field. The present invention can effectively improve the output differential pressure of the average velocity tube flowmeter, improve the accuracy of the low flow measurement of the average velocity tube, and thus expand the application scope of the differential pressure flowmeter. The present invention adopts the following technical solutions:

[0013] A concave arc dual-flow average velocity tube flowmeter comprises a detection rod inserted into a measuring pipeline along the diameter, a total pressure tube and a static pressure tube arranged in the detection rod, the total pressure tube is located on the upstream surface, and the static pressure tube is located on the downstream surface, and total pressure holes and static pressure holes are arranged on the upstream surface and downstream surface of the detection rod, all the total pressure holes are connected with the total pressure tube, and the average total pressure p is drawn out from the total pressure tube; all the static pressure holes are connected with the static pressure tube, and the static pressure p is drawn out from the static pressure tube; the difference between the measured total pressure p and the static pressure p is used to reflect the size of the average flow velocity on the pipeline cross section, and the characteristic is that the cross-sectional shape of the detection rod is similar to a rhombus, and the four sides are all concave arcs, the upstream surface and the downstream surface are both convex arcs, and the concave arc edges are streamlined at the junction.

[0014] Preferably, the curvature of each concave arc edge is as large as possible while satisfying the processing requirements. The flow meter according to claim 1 is characterized in that the ratio of the concave arc radius (R1) of each concave arc edge to the circumscribed circle diameter (L1) of the detection rod is controlled within a range of 0.25 to 3. The flow meter is bilaterally symmetrical, and the total pressure pipe and the static pressure pipe can be interchanged to achieve dual-direction flow measurement.

[0015] Due to the adoption of the above technical solution, the present invention has the following advantages compared with the prior art:

[0016] (1) Based on the method of combining computational fluid dynamics simulation with theoretical analysis of the working principle of the average velocity tube and the pressure taking method of the pressure taking hole, the influence of the cross-sectional shape of the detection rod on the total pressure and static pressure of the average velocity tube is studied from the perspective of the flow field development mechanism, thereby realizing the structural optimization of the cross-sectional shape of the concave arc dual-flow direction average velocity tube flowmeter. Within a large water flow measurement range, the concave arc dual-flow direction average velocity tube flowmeter can output a large and stable differential pressure, which is 2 to 3 times higher than that of the traditional average velocity tube structure, and the flow measurement repeatability and linearity are good, which can reach ±(1 to 2)%, thereby significantly improving the accuracy of flow measurement.

[0017] (2) The concave arc dual-flow direction average velocity tube flowmeter has a symmetrical structure, and the total pressure hole and the static pressure hole have the same pressure measurement method. It only needs to be equipped with a differential pressure transmitter to realize dual flow direction measurement of the fluid, which can reduce the measurement cost of the average velocity tube flowmeter.

[0018] (3) The concave arc dual-flow average velocity tube flowmeter has no moving parts. All parts can be made of universal profiles. The symmetrical structure design makes it easy to install and maintain. It can be disassembled and assembled without interrupting the flow. The overall economic cost is low and no material waste will be generated.

[0019] (4) Due to the simplicity of the structure and the standard universality of all components, the structural parameters of the concave arc dual-flow uniform velocity tube flowmeter can be analyzed and calculated using existing commercial finite element calculation software, which makes it convenient for engineering technicians to flexibly select different structural parameter values ​​to optimize the design of the device according to different actual engineering needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 These are the four most widely used uniform velocity tube cross-section shapes.

[0021] Figure 2 It is the structure of the concave arc dual-flow direction average velocity tube flowmeter of the present invention (left figure) and the schematic diagram of the cross-sectional shape (right figure).

[0022] Explanation of the numbers in the figure: 1 measuring pipe; 2 detection rod; 3 total pressure pipe; 4 static pressure pipe; 5 total pressure hole; 6 static pressure hole; D detection rod length; L1 detection rod circumscribed circle diameter; R1 concave arc radius; R2 convex arc radius; L2 convex arc width; t platform width; ΔL pressure hole distance.

[0023] Custom: When R1=0, it means that the structure of this segment is a straight edge.

[0024] Figure 3 It is a schematic diagram of the position of the pressure taking holes of the concave arc dual-flow direction average velocity tube flowmeter of the present invention.

[0025] Explanation of the numbers in the figure: r1 is the distance from the center of the first pair of pressure holes to the center of the pipe; r2 is the distance from the center of the second pair of pressure holes to the center of the pipe; R measures the inner radius of the pipe.

[0026] Figure 4 It is a velocity simulation cloud diagram of the effect of the detection rod on the flow field inside the measurement pipeline.

[0027] Figure 5-Figure 7 This is a comparison chart of simulation results of differential pressure signals generated by different detection rod cross-sectional shapes.

[0028] Figure 8 It is a comparison chart between simulation data and measured data of the concave arc dual-flow direction average velocity tube flowmeter of the present invention at DN200.

[0029] Fig. 9 It is a comparison chart of static test calibration results of the concave arc dual-flow direction average velocity tube flowmeter and the diamond-shaped average velocity tube flowmeter of the present invention. DETAILED DESCRIPTION

[0030] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0031] like Figure 2 , Figure 3 As shown, the concave arc dual-flow average velocity tube flowmeter of the present invention is a differential pressure device composed of a detection rod 2, a total pressure tube 3, a static pressure tube 4, a total pressure hole 5 and a static pressure hole 6. The concave arc dual-flow average velocity tube flowmeter is a hollow metal rod, namely the detection rod 2, which is inserted into the measuring pipe along the diameter. There are paired total pressure holes 5 in the flow direction to measure the total pressure. All the total pressure holes 5 are connected to the total pressure tube 3, and the average total pressure p1 is drawn from the upper part of the total pressure tube 3. There are paired static pressure holes 6 for measuring static pressure on the back flow surface of the detection rod 2, which are connected to the static pressure tube 4, and the static pressure p2 is drawn from the upper part of the static pressure tube 4. The concave arc dual-flow average velocity tube flowmeter uses the difference between the measured total pressure p1 and the static pressure p2 to reflect the size of the average flow velocity on the pipe cross section.

[0032] According to Bernoulli's equation, ignoring factors such as friction and fluid height difference, we have

[0033]

[0034] Where: ρ—fluid density, (kg / m 3 ); v1—flow velocity at the total pressure hole 5, (m / s); p1—static pressure at the total pressure hole 5, (Pa); v2—flow velocity at the static pressure hole 6, (m / s); p2—static pressure at the static pressure hole 6, (Pa).

[0035] The kinetic energy of the fluid in the total pressure hole 5 of the concave arc dual-flow average velocity tube flowmeter is converted into potential energy, so the fluid is basically stagnant, that is, the dynamic pressure is 0, so v1 = 0, and formula (1) can be simplified to

[0036]

[0037]

[0038] Where: Δp = p1-p2

[0039] Where: Δp—differential pressure, Pa (Pa); K is the instrument factor, is the average flow velocity of the fluid (m / s).

[0040] If expressed in terms of volume flow and mass flow, the basic flow calculation formula for the concave arc dual-flow average velocity tube flowmeter is:

[0041]

[0042] q m =q v ρ (5)

[0043] Where: q v —Volume flow rate of fluid, (m 3 / s);q m —Mass flow rate of fluid, (kg / s);

[0044] ε—Flow rate expansion coefficient when the fluid flows through the detection rod 2 under working conditions, for incompressible fluid:

[0045] ε=1; for compressible fluid: ε<1; A—measurement of the cross-sectional area of ​​pipe 1 under working condition, (m 2 ).

[0046] Based on theoretical analysis of the working principle of the average velocity tube flowmeter, the pressure collection method of the total pressure hole and the static pressure hole, etc., the computational fluid dynamics simulation (CFD) method is used to study the influence of the cross-sectional shape of the detection rod on the flow field and differential pressure signal inside the measuring pipeline. As shown in Table 1, different computational fluid dynamics simulation models are obtained by changing the structural parameters on the concave arc detection rod cross section. The flow field of each model is simulated and the total pressure and static pressure on the detection rod are extracted to calculate the differential pressure value. Figure 4As shown in the figure, by analyzing the flow field velocity cloud diagrams generated by each concave arc detection rod model inside the measuring pipe, it is shown that the larger the diameter L1 of the circumscribed circle of the detection rod is under the same measuring pipe diameter, the thicker the boundary layer generated downstream of the detection rod is, and the correspondingly larger the differential pressure value is. Figure 5 , Figure 6 , Figure 7 The simulation results show that among the structural parameters on the concave arc detection rod cross section, the size of the concave arc radius R1 has the highest influence on the differential pressure value, while other parameters such as the detection rod length D, convex arc radius R2, convex arc width L2, platform width t and pressure tapping hole distance ΔL have little influence on the differential pressure value and can be adjusted accordingly according to the actual working conditions and processing technology level.

[0047] The optimal static test calibration results obtained by the present invention according to the structural parameters of model 7 are shown in Table 2. The differential pressure increases significantly in a larger range, reaching more than 65Kpa at a fluid flow rate of 5m / s; the flow measurement repeatability and linearity are good, the repeatability is within 0.5%, and the outflow coefficient linearity is within 2%. Compare the simulation data with the measured data,

[0048] like Figure 8 As shown, there is little difference between the two, which verifies the accuracy of the research method that combines computational fluid dynamics simulation with theoretical analysis such as the working principle of the average velocity tube.

[0049] like Fig. 9 As shown, based on the same measuring tube diameter and the same detection rod circumscribed circle diameter, the calibration results of the present invention and the diamond flowmeter under the same water flow static test are compared. Under the same flow rate, the output differential pressure of the present invention is significantly improved, so the present invention has obvious measurement advantages in a larger flow measurement range, especially has a greater impact on improving the measurement accuracy of small flow.

[0050] Table 1 Simulation models of different concave arc detection rod cross-section shapes

[0051]

[0052] Table 2 Calibration data of concave arc dual flow direction average velocity tube flowmeter at DN100 water flow

[0053]

Claims

1. A concave arc dual-flow average velocity tube flowmeter, comprising a detection rod inserted into a measuring pipe along the diameter, a total pressure pipe and a static pressure pipe arranged in the detection rod, the total pressure pipe is located on the upstream side, the static pressure pipe is located on the downstream side, and total pressure holes and static pressure holes are arranged on the upstream side and the downstream side of the detection rod, all the total pressure holes are connected to the total pressure pipe, and the average total pressure is drawn from the total pressure pipe. p All static pressure holes are connected to the static pressure pipe, and the static pressure is drawn from the static pressure pipe. p ; Using the measured total pressure p With static pressure p The difference between the two obtains the average flow velocity on the pipe cross section, which is characterized by: The cross-sectional shape of the detection rod is similar to a rhombus, with all four sides being concave arcs, the upstream surface and the downstream surface being convex arcs, and the concave arc edges connecting are streamlined; the flow meter is bilaterally symmetrical, and the total pressure pipe and the static pressure pipe can be interchanged to realize dual-direction flow measurement.

2. The flow meter according to claim 1, characterized in that While meeting the processing requirements, the greater the curvature of each concave arc edge, the better.

3. The flow meter according to claim 1, characterized in that: The ratio of the concave arc radius R1 of each concave arc edge to the circumscribed circle diameter L1 of the detection rod is controlled within a range of 0.25-3.

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