Ultrasonic gas meter module with low reynolds number flow regime automatic compensation

Abstract

The application discloses a kind of low Reynolds number flow state automatic compensation's ultrasonic gas meter module, belong to ultrasonic wave gas meter technical field, including main flow channel, main flow channel is similar venturi tube structure, is provided with rectifier and ultrasonic sensor in the input end and output end of main flow channel, is provided with several bypass flow channel outside the output end of main flow channel, bypass flow channel evenly distributes around main flow channel axis.The main flow channel is similar venturi tube structure, with larger cavity space, the profile of measurement section is circular arc tangent smooth connection, with smaller pressure loss and good rectification effect, expand the upper limit of flow measurement;It can simultaneously reduce, slow down the separation and transition of demarcation layer, even in turbulent form, fluid each layer particle exchange is less, less pollutant deposition, ultrasonic sensor arranged to reflect, can according to table shell cavity space amplification axis length, obtain enough measurement time and time difference, also without the influence of sound energy loss caused by reflection and reflection surface dirtiness caused sound channel length variation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ultrasonic gas meters, and particularly relates to an ultrasonic gas meter module capable of automatically compensating for low Reynolds number flow state. BACKGROUND

[0002] Gas ultrasonic metering technology has been widely applied in the natural gas trade metering industry, and the promulgation of relevant international and national standards and verification regulations has laid a technical foundation for the application and promotion of ultrasonic flow meters. According to the relevant requirements of the national standard GB / T39841-2021 Ultrasonic Gas Meter, the measurement range of ultrasonic gas meters for urban household and small and medium-sized commercial and industrial users is from 0.016 m 3 / h to 10 m 3 / h, with a pressure loss of not more than 250 Pa (with valve), and an accuracy requirement of not less than 1.5%; among them, the flow range of G1.6 household gas meters is from 0.016 m 3 / h to 2.5 m 3 / h, and the Reynolds number of the conventional flow channel design in this flow range is 15-4000, and the fluid form changes greatly, spanning three flow states of laminar flow, transitional flow and turbulent flow; how to effectively solve the influence of flow state change on the measurement accuracy and control the manufacturing and application cost puts high requirements on the design of the ultrasonic gas meter module.

[0003] Reynolds number is a dimensionless number that can be used to represent the flow condition of a fluid. Re=ρυd / μ, where ρ, υ, μ are the density, flow velocity and viscosity coefficient of the fluid respectively, and d is a characteristic length. Small Reynolds number means that the viscous force between particles plays a major role in fluid flow, and the particles flow regularly parallel to the inner wall of the pipeline, showing laminar flow state. Large Reynolds number means that inertial force plays a major role, and the fluid shows turbulent flow state. Generally, the Reynolds number of the pipeline is Re<2000 for laminar flow state, Re>4000 for turbulent flow state, and Re is between 2000 and 4000 for transitional flow state. Under different flow states, the motion law and flow velocity distribution of the fluid are different, causing the ratio of the average flow velocity υ to the maximum flow velocity υ max is also different, such as Figure 5 for laminar flow state with Reynolds number less than 2000, Figure 6 for turbulent flow state with Reynolds number greater than 4000.

[0004] The discharge coefficient C of differential pressure flowmeter (flow resistance) such as orifice plate flowmeter, venturi flowmeter, etc. varies with Reynolds number; when the value of β (d0 / D) is 0.2, where d0 is the smallest diameter of the main flow passage of the flowmeter and D is the diameter of the input end of the flowmeter, the discharge coefficient C remains basically constant when the Reynolds number is greater than 1000, where the discharge coefficient C is about 0.59; when the value of β (d0 / D) is 0.7, the discharge coefficient C also remains constant when the Reynolds number is greater than 100000, about 0.69; where the discharge coefficient C is calculated as In the formula, qm is the mass flow, Δp is the differential pressure, and ρ is the density of the fluid. In most cases, the greater the value of β, the greater the discharge coefficient C. However, when the Reynolds number is less than 600, the discharge coefficient of a large β value decreases significantly with the decrease of the Reynolds number, and when the Reynolds number decreases to 20, the discharge coefficient of a large β value is smaller than that of a small β value. Figure 10 This basic flow variation rule lays the theoretical foundation for the micro-pore bypass flow channel to balance and compensate for the large measurement value of the main flow channel at low Reynolds numbers.

[0005] During the operation of a gas meter, different flow rates during the operation of the gas meter can form laminar flow or turbulent flow, thereby affecting the measurement results. Most current ultrasonic gas meters use a reflective metering module, the flow passage cross section of which is a rectangular structure, and the gas flow passage is divided into several 2mm thin channels by setting a flow grid in the flow passage. Therefore, the gas flow state of a single thin layer can be controlled to be laminar flow within a Reynolds number of 2000, thereby avoiding the influence of different fluid forms on the measurement accuracy. However, the feature structure has the following defects.

[0006] 1. The rectangular cross section design limits the design of the sound channel length. Even if a 45° angle single reflection is used, the velocity vector along the sound channel direction is only which leads to a small difference in measurement time and limits the measurement accuracy.

[0007] 2. It is only suitable for clean gas. Once the reflective surface is contaminated, the sound path length changes, thereby affecting the measurement accuracy.

[0008] 3. Each reflection will lose sound energy, about 3-5dB; at the same time, the echo signal is prone to distortion, and more energy resources are needed for compensation.

[0009] 4. The pressure loss is large at high flow rates. A single size module has a narrow flow range, and the range ratio is not more than 200:1. More modules are needed to cover more flow measurement requirements, which increases the manufacturing cost.

[0010] Therefore, it is necessary to design an ultrasonic gas meter module with low Reynolds number flow state automatic compensation to solve these problems. SUMMARY

[0011] The application provides a low Reynolds number flow state automatic compensation ultrasonic gas meter module with a large range, low pressure loss, dirt resistance and low overall manufacturing cost.

[0012] To solve the above technical problems, the application adopts the technical scheme of:

[0013] The low Reynolds number flow state automatic compensation ultrasonic gas meter module comprises a main flow channel, the main flow channel is a venturi-like structure, a flow regulator and an ultrasonic sensor are arranged at the input end and the output end of the main flow channel, and a plurality of bypass flow channels are arranged outside the output end of the main flow channel, and the bypass flow channels are uniformly distributed around the axis of the main flow channel.

[0014] Preferably, the bypass flow channel comprises an air outlet pipe sleeved outside the output end of the main flow channel, the air outlet pipe is connected with the main flow channel through a flow limiting orifice plate, a plurality of through holes are formed in the flow limiting orifice plate, and the plurality of through holes are uniformly distributed around the axis of the main flow channel.

[0015] In this way, the bypass flow channel is combined, and the assembly is convenient to install and fix. The air outlet pipe is in airtight connection with the gas meter air outlet pipe joint, so that the gas flowing through the main flow channel and the bypass flow channel flows out of the gas meter.

[0016] Preferably, the main flow channel is divided into an upstream tapered section, a throat and a downstream tapered section, the throat is the position with the smallest diameter on the main flow channel, the upstream tapered section is the position between the input end of the main flow channel and the throat, the downstream tapered section is the position between the throat and the output end of the main flow channel, the diameter D of the input end of the main flow channel is greater than the diameter of the output end, the diameter of the output end of the main flow channel is greater than the diameter d of the throat, and the ratio d / D of the diameter d of the throat to the diameter D of the input end is 0.4-0.6.

[0017] In this way, the stability of the flow state is realized by controlling the range of the diameter of the throat and the diameter of the input end, and the influence of the vortex generated after the installation of the fittings on the detection result is reduced.

[0018] Preferably, the number of the through holes is 9-18, the diameter d of the through holes is 1 / 15-1 / 20 of the diameter D of the input end of the main flow channel, and the diameter d of the through holes is greater than or equal to 1.6 mm. b Preferably, the number of the through holes is 9-18, the diameter d of the through holes is 1 / 15-1 / 20 of the diameter D of the input end of the main flow channel, and the diameter d of the through holes is greater than or equal to 1.6 mm. b

[0019] In this way, the choke flow can be avoided.

[0020] ​Preferably, an outer protective skirt is further sleeved outside the main flow channel, the outer protective skirt is connected with the air outlet pipe, and the length of the outer protective skirt is not less than five times of the diameter d of the through-flow hole. b

[0021] In this way, the influence of external airflow can be reduced.

[0022] Preferably, an inner protective skirt is further fixedly arranged at the output end of the main flow channel, and the length of the inner protective skirt is not less than the diameter d of the through-flow hole. b

[0023] In this way, the airflow in the main flow channel and the bypass airflow are separated and do not affect each other.

[0024] Preferably, the length of the main flow channel is L, the length of the upstream tapered section is 3 / 4 of the length of the main flow channel, the length of the downstream tapered section is 1 / 4 of the length of the main flow channel, the inner wall profile of the upstream tapered section and the downstream tapered section are both smooth circular arc tangent lines, and the tapering angle a of the inner wall of the upstream tapered section is 3-5°.

[0025] In this way, the pressure loss can be reduced, the fluid form in the main flow channel can be stabilized, and the measurement accuracy can be improved.

[0026] Preferably, the flow straightener and the ultrasonic sensor comprise an air inlet flow straightener, an air outlet flow straightener, an air inlet ultrasonic sensor and an air outlet ultrasonic sensor, the air inlet flow straightener is arranged at the input end of the main flow channel, the air inlet ultrasonic sensor is arranged on the air inlet flow straightener, the air outlet flow straightener is arranged in the air outlet pipe, the air outlet ultrasonic sensor is arranged on the air outlet flow straightener, and the output end of the air inlet ultrasonic sensor is opposite to the input end of the air outlet ultrasonic sensor.

[0027] In this way, the vortex flow into and out of the main flow channel can be reduced, and the ultrasonic sensor can be stably positioned.

[0028] Preferably, an air inlet pipe is further connected to the input end of the main flow channel, and the air inlet flow straightener is arranged in the air inlet pipe.

[0029] In this way, the assembly can be conveniently installed and fixed.

[0030] The present application has the advantages and positive effects that:

[0031] 1. The main flow channel has a large cavity space, and the measurement section profile is smoothly connected by circular arc tangent lines, so that even in a turbulent form, the exchange of particles of each layer of fluid is less, and the deposition of pollutants is less.

[0032] ​​2. The pair of ultrasonic sensors are installed at both ends of the main flow channel axis, and the axis length can be enlarged according to the space of the watch case cavity. The sound channel direction is the fluid motion direction, so the effective sound channel length of the design is the actual sound channel length, and sufficient measurement time and time difference can be obtained to ensure the measurement accuracy.

[0033] 3. The pair of sound channel arrangement has no sound energy loss caused by reflection, and the pair of sound channel arrangement has no influence of sound channel length change caused by reflection surface dirt.

[0034] 4. The main flow channel adopts a Venturi-like structure, has small pressure loss and good flow straightening effect, and can reduce and slow down the separation and transition of the boundary layer.

[0035] 5. The flow balance effect of the bypass flow channel extends the lower limit of the flow measurement, and the range ratio can reach 1000:1, thereby improving the production efficiency and reducing the manufacturing cost. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0037] Figure 1 is the overall structure of the low Reynolds number flow state automatic compensation ultrasonic gas meter module described in the present application.

[0038] Figure 2 is the internal structure of the low Reynolds number flow state automatic compensation ultrasonic gas meter module described in the present application.

[0039] Figure 3 is the main flow channel segmented structure of the low Reynolds number flow state automatic compensation ultrasonic gas meter module described in the present application.

[0040] Figure 4 is the through-flow hole distribution structure of the low Reynolds number flow state automatic compensation ultrasonic gas meter module described in the present application.

[0041] Figure 5 is the laminar flow pattern for Reynolds number less than 2000.

[0042] Figure 6 is the turbulent flow pattern for Reynolds number greater than 4000.

[0043] Figure 7 is the installation structure of the measurement module in the sealed watch case.

[0044] Figure 8 is a schematic diagram of CFD simulated velocity distribution in the duct region;

[0045] Figure 9 is a schematic diagram of CFD measured deviation, where the horizontal axis is flow rate m 3 / h, and the vertical axis is measured deviation;

[0046] Figure 10 is a schematic diagram of the relationship between discharge coefficient C and Reynolds number and d / D.

[0047] The reference signs are explained as follows:

[0048] 1, inlet pipe; 2, main flow channel; 21, upstream converging section; 22, throat; 23, downstream diverging section; 3, outlet pipe; 4, flow restriction orifice; 5, inlet flow straightener; 6, inlet flow fairing; 7, inlet ultrasonic sensor; 8, through-flow hole; 9, outlet flow straightener; 10, outlet ultrasonic sensor; 11, outer protective skirt; 12, inner protective skirt. DETAILED DESCRIPTION

[0049] In the description of the present application, it needs to be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified and limited, the term "a plurality of" means two or more.

[0050] In the description of the present application, it needs to be noted that, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be direct connection, or indirect connection through intermediate medium, or internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0051] The present application will be further described below in conjunction with the drawings:

[0052] Example 1: as Figures 1-10As shown, an ultrasonic gas meter module with low Reynolds number flow state automatic compensation includes a main flow channel 2, which is a venturi-like structure. A flow regulator and an ultrasonic sensor are arranged at the input end and the output end of the main flow channel 2. A plurality of bypass flow channels are arranged outside the output end of the main flow channel 2 and are uniformly distributed around the axis of the main flow channel 2.

[0053] Specifically, the bypass flow channel includes an air outlet pipe 3 sleeved outside the output end of the main flow channel 2. The air outlet pipe 3 is connected to the main flow channel 2 through a flow limiting orifice plate 4. A plurality of through holes 8 are arranged on the flow limiting orifice plate 4 and are uniformly distributed around the axis of the main flow channel 2. In this way, the bypass flow channel is formed, and the assembly is easy to install and fix. The air outlet pipe is in airtight connection with a gas meter air outlet pipe joint, so that the gas flowing through the main flow channel and the bypass flow channel flows out of the gas meter.

[0054] Further, the main flow channel 2 is divided into an upstream converging section 21, a throat section 22, and a downstream diverging section 23. The throat section 22 is the position with the smallest diameter on the main flow channel 2. The upstream converging section 21 is the position between the input end of the main flow channel 2 and the throat section 22. The downstream diverging section 23 is the position between the throat section 22 and the output end of the main flow channel 2. The diameter D of the input end of the main flow channel 2 is greater than the diameter of the output end. The diameter of the output end of the main flow channel 2 is greater than the diameter d of the throat section 22. The ratio d / D of the diameter d of the throat section 22 to the diameter D of the input end is 0.4-0.6, i.e., the β of the device is 0.4-0.6. In this way, the stability of the flow state is realized by controlling the range of the diameter of the throat section 22 and the diameter of the input end, and the influence of the vortex generated after the installation of the fittings on the detection result is reduced.

[0055] Further, the number of the through holes 8 is 9-18. The diameter d b of the through holes 8 is 1 / 15-1 / 20 of the diameter D of the input end of the main flow channel 2, and the diameter d b of the through holes 8 is greater than or equal to 1.6 mm. In this way, choking flow can be avoided.

[0056] Further, an outer protective skirt 11 is sleeved outside the main flow channel 2. The outer protective skirt 11 is connected to the air outlet pipe 3, and the length of the outer protective skirt 11 is not less than five times the diameter d b of the through holes 8. In this way, the influence of external airflow can be reduced.

[0057] Further, an inner protective skirt 12 is fixedly arranged at the output end of the main flow channel 2. The length of the inner protective skirt 12 is not less than the diameter d b of the through holes 8. In this way, the gas flow in the main flow channel 2 and the bypass gas flow are separated and do not affect each other.

[0058] Specifically, the length of the main flow channel 2 is L, the length of the upstream tapered section 21 is 3 / 4 of the length of the main flow channel 2, and the length of the downstream tapered section 23 is 1 / 4 of the length of the main flow channel 2. The inner wall profiles of the upstream tapered section 21 and the downstream tapered section 23 are both smooth circular arc tangent lines, and the tapering angle α of the inner wall of the upstream tapered section 21 is 3°-5°. Such a configuration can reduce pressure loss, stabilize the fluid form in the main flow channel, and improve measurement accuracy.

[0059] The Venturi structure is a rapid contraction, and the main flow channel 2 of the device adopts a tapered type similar to a Venturi tube and is constrained by size. The average flow rate is obtained by measuring the central axis flow rate in the main flow channel which is a similar Venturi tube. Figure 6 When the Reynolds number is greater than 4000, the fluid form is stable and reliable, and good measurement accuracy can be maintained without any correction. When the Reynolds number is less than 2000, Figure 5 the fluid flow state in the axial region gradually becomes sharp, and the central axis flow rate gradually increases compared with the average flow rate. When the Reynolds number is less than 30, the central axis flow rate increases by nearly 50% compared with the average flow rate. The bypass flow channel can balance and compensate for the measurement defects of the low Reynolds number Venturi flow channel.

[0060] Specifically, the flow straightener and the ultrasonic sensor include an air inlet flow straightener 5, an air outlet flow straightener 9, an air inlet ultrasonic sensor 7, and an air outlet ultrasonic sensor 10. The air inlet flow straightener 5 is installed at the input end of the main flow channel 2, the air inlet ultrasonic sensor 7 is installed on the air inlet flow straightener 5, and an air inlet flow guide cover 6 is also installed on the air inlet flow straightener 5. The air outlet flow straightener 9 is installed in the air outlet pipe 3, and the air outlet ultrasonic sensor 10 is installed on the air outlet flow straightener 9. The transmitting end of the air inlet ultrasonic sensor 7 is opposite to the receiving end of the air outlet ultrasonic sensor 10. Such a configuration can reduce the vortex flow into and out of the main flow channel 2, and can also stabilize the positioning of the ultrasonic sensor.

[0061] An air inlet pipe 1 is also connected to the input end of the main flow channel 2, and the air inlet flow straightener 5 is located in the air inlet pipe 1, which facilitates the installation and fixation of the components. An air inlet flow guide cover is also installed on the air inlet flow straightener, which can smoothly guide the airflow flowing to the back of the air inlet ultrasonic sensor to the surrounding area, so that the airflow flows into the main flow channel through the air inlet flow straightener.

[0062] The working process of the embodiment is as follows:

[0063] The present application focuses on the measurement of small flow and micro flow, and needs to be installed in a sealed watch case. The air outlet pipe 3 is connected to the output end of the sealed watch case. In operation, the gas passes through the air inlet flow straightener 5 into the main flow channel 2, and then passes through the air outlet flow straightener 9 out of the main flow channel 2. In this process, the volume of the gas is compressed when it flows from the input end with a larger diameter to the throat 22 with a smaller diameter, so the flow rate increases. After passing through the throat 22, the volume of the gas expands, and the flow rate decreases.

[0064] The value of β of the flow channel type Venturi tube is generally 0.8; the value of β of the micro-hole bypass flow channel is designed to be 0.2. Referring to Figure 10 When the Reynolds number is greater than or equal to 2000, the corresponding flow rate is greater than or equal to 1.4 m 3 / h; the bypass flow channel outflow coefficient is about 0.6; the outflow coefficient C of the type Venturi tube is about 1.24; when the Reynolds number is 60, the corresponding flow rate is about 0.04 m 3 / h, the outflow coefficient of the type Venturi tube is about 0.94, and the outflow coefficient of the bypass flow channel is about 0.68. This means that the flow rate decreases, and the flow rate ratio of the bypass flow channel outflow increases; when the Reynolds number is less than or equal to 24, the corresponding flow rate is 0.016 m 3 / h, the outflow coefficient of the type Venturi tube will be 0.66, and the outflow coefficient of the bypass flow channel will also be 0.66, which means that the flow rate ratio of the bypass flow channel outflow at this time increases by nearly 50% compared to the high Reynolds number. The increased flow rate of the bypass flow channel reduces the flow rate of the main flow channel, which practically compensates for the defect that the type Venturi tube of the main flow channel causes the measurement deviation of the high flow rate area of the central axis to increase at low Reynolds number, such as Figure 5 .

[0065] Based on the relevant national standards, the measurement accuracy is better than ±3% between Q min ~ Q t .

[0066] In this embodiment, the minimum value Q min is 0.016 m 3 / h, and the key node Q t is 1 m 3 / h. Taking this flow rate range as an example, the embodiment is explained in a theoretical calculation manner:

[0067] I. Ensure that the time measurement uncertainty is better than ±2%;

[0068] a) Main flow channel 2 throat diameter d calculation:

[0069] The flow rate range is 0.016~10 m 3 / h, the Reynolds number is 15~15000, and the maximum flow rate of the main flow channel 2 throat diameter is not more than 25 m / s.

[0070] The calculation shows that the throat diameter d is not less than 11.9 mm; considering that the outer diameter of the transmitting and receiving ports of the ultrasonic sensor is 14 mm, the main flow channel 2 throat diameter is designed to be 16 mm.

[0071] b) Sound channel length L calculation:

[0072] At 1 atmosphere pressure, 20°C, the natural gas sound speed is about 427.7 m / s, the 70 mm sound channel length, the minimum flow rate is 0.01 m / s, and the time difference is about 7.65 ns; the time measurement accuracy of ±2% is ±0.15 ns, which is about ±2% of the time measurement accuracy. The existing ultrasonic chip time resolution is 30 ps, and the measurement accuracy is considered according to three times the resolution, and the time measurement accuracy can be better than 100 ps, that is, ±0.1 ns; therefore, for the jet sound channel arrangement, the 70 mm sound channel length, and the time measurement accuracy of ±0.15 ns, the time measurement uncertainty of ±2% can meet the requirements.

[0073] c) Main flow channel 2 inlet and outlet diameter D:

[0074] According to the actual flow area (πD 2 / 4 minus the sensor and sleeve cross-sectional area and the flow guide plate cross-sectional area) of the main flow channel 2 inlet and outlet, it is about 32-36 mm.

[0075] II. Main flow channel 2 throat position

[0076] The main flow channel 2 throat position can be controlled to be at the sound channel 3 / 4, that is, from the beginning of the sound channel to 52-53 mm.

[0077] III. Main flow channel 2 profile

[0078] The main flow channel 2 throat is a parallel point, which is smoothly connected to the outer end of the inlet diameter D by an upstream circular arc tangent; and is smoothly connected to the inner ring of the outlet orifice plate by a downstream circular arc tangent.

[0079] IV. Flow limiting orifice plate 4 hole diameter and number

[0080] According to the reference department standard HG / T20570-95 "Process system engineering design technical regulations", the β value should be less than 0.2. According to the existing industrial mold machining and parting precision requirements, 1.6-2.4 mm can be selected as the hole diameter d b of the initial prototype flow limiting orifice plate 4 through flow hole 8, and the throat area is 10%-15% of the total flow area of the flow limiting orifice plate 4, and the number of flow limiting orifice plate 4 through flow holes 8 can be selected as 8-12.

[0081] V. CFD flow state simulation

[0082] After the main structure parameters of the ultrasonic gas meter module are preliminarily selected, a large range flow state simulation is carried out through the CFD flow state simulation software, such as 0.016-16 m 3 / h; the velocity distribution and streamline development are observed, such as the attached drawing-08; the streamline velocity in the sound channel area is detected; and the average flow velocity is obtained.

[0083] According to the following performance priority requirements, the related structure parameters are adjusted, the simulation test is grouped and combined, the flow state development and change trend caused by the parameter change and the influence on the measurement accuracy are determined, so as to guide the fine adjustment of the related parameters of the 3D printing module:

[0084] a) The flow state in the measuring flow channel is stable, and the flow line is not crossed.

[0085] b) The flow deviation is in the expected range, the large flow (greater than 1.6m 3 / h is better than ± 1%, the small flow (0.1-1.6m 3 / h) is better than ± 3%, and the micro flow (less than 0.1m 3 / h) is better than ± 6%;

[0086] c) The pressure loss is small, and meets the requirements of the national standard.

[0087] Six, CFD flow state simulation and module parameter setting

[0088] CFD flow state simulation iteration is carried out according to the calculation parameters. The main module parameters include: the input end diameter D of the main flow channel 2, the output end diameter of the main flow channel 2, the diameter d of the throat 22, the position of the throat diameter 22 on the main flow channel 2, the hole diameter d b and the number of the through-flow hole 8, the length of the outer protective skirt 11 and the inner protective skirt 12, etc. When the simulation measurement flow deviation meets the expected requirements, and the pressure loss meets the requirements of the national standard, the flow state simulation module parameter setting can be determined.

[0089] The above has carried out the detailed description to one embodiment of the present application, but the content described is only the preferred embodiment of the present application, and cannot be considered as being used to limit the implementation range of the present application. Any equivalent change and improvement made according to the application scope of the present application should still belong to the patent coverage range of the present application.

Claims

1. A low Reynolds number flow state automatic compensation ultrasonic gas meter module, comprising a main flow channel (2), wherein the main flow channel (2) is a Venturi tube-like structure, and a rectifier and an ultrasonic sensor are provided at both the input and output ends of the main flow channel (2), characterized in that: Several bypass channels are provided outside the output end of the main channel (2), and the bypass channels are evenly distributed around the axis of the main channel (2). The bypass channel includes an exhaust pipe (3) fitted on the outside of the output end of the main channel (2). The exhaust pipe (3) is connected to the main channel (2) through a flow-limiting orifice plate (4). A plurality of flow holes (8) are opened on the flow-limiting orifice plate (4). The plurality of flow holes (8) are evenly distributed around the axis of the main channel (2). The main channel (2) is divided into an upstream tapering section (21), a throat (22), and a downstream expanding section (23). The throat (22) is the position with the smallest diameter on the main channel (2). The upstream tapering section (21) is the position between the input end of the main channel (2) and the throat (22). The downstream expanding section (23) is the position between the throat (22) and the output end of the main channel (2). The diameter D of the input end of the main channel (2) is greater than the diameter of the output end. The diameter of the output end of the main channel (2) is greater than the diameter d of the throat (22). The ratio d / D of the diameter d of the throat (22) to the diameter D of the input end is 0.4 to 0.

6. The number of flow passages (8) is 9-18, and the diameter d of the flow passages (8) is... b The diameter of the main channel (2) input end is 1 / 15 to 1 / 20 of the diameter D, and the diameter of the flow hole (8) is d. b ≥1.6mm.

2. The ultrasonic gas meter module with low Reynolds number flow state automatic compensation according to claim 1, characterized in that: An outer protective skirt (11) is fitted on the outside of the main flow channel (2). The outer protective skirt (11) is connected to the air outlet pipe (3), and the length of the outer protective skirt (11) is not less than the diameter d of the flow hole (8). b Five times.

3. The ultrasonic gas meter module with low Reynolds number flow state automatic compensation according to claim 1, characterized in that: The output end of the main channel (2) is also fixedly provided with an inner skirt (12), the length of which is not less than the diameter d of the flow hole (8). b .

4. The ultrasonic gas meter module with low Reynolds number flow state automatic compensation according to claim 1, characterized in that: The length of the main channel (2) is L, the length of the upstream tapering section (21) is 3 / 4 of the length of the main channel (2), the length of the downstream expanding section (23) is 1 / 4 of the length of the main channel (2), the inner wall contours of the upstream tapering section (21) and the downstream expanding section (23) are both smooth circular arc tangents, and the tapering angle α of the inner wall of the upstream tapering section (21) is 3° to 5°.

5. The ultrasonic gas meter module with low Reynolds number flow state automatic compensation according to claim 1, characterized in that: The rectifier and the ultrasonic sensor include an intake rectifier (5), an exhaust rectifier (9), an intake ultrasonic sensor (7), and an exhaust ultrasonic sensor (10). The intake rectifier (5) is installed at the input end of the main channel (2). The intake ultrasonic sensor (7) is installed on the intake rectifier (5). The exhaust rectifier (9) is installed inside the exhaust pipe (3). The exhaust ultrasonic sensor (10) is installed on the exhaust rectifier (9), and the output end of the intake ultrasonic sensor (7) is opposite to the input end of the exhaust ultrasonic sensor (10).

6. The ultrasonic gas meter module with automatic compensation for low Reynolds number flow state according to claim 5, characterized in that: An intake pipe (1) is also connected to the output end of the main channel (2), and the intake rectifier (5) is located inside the intake pipe (1).

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