阅读说明：本技术 一种用于测量微小流量的差压流量计及测量方法 (Differential pressure flowmeter for measuring micro flow and measuring method ) 是由 郭素娜 迟秋爽 相诺林 王帆 赵宁 方立德 于 2021-08-02 设计创作，主要内容包括：本发明提供了一种用于测量微小流量的差压流量计及测量方法。本发明中差压流量计采用螺旋管作为微小流体流量的测试管段,螺旋管的两端分别通过变径卡套连接内径比螺旋管内径大的管道,在螺旋管的两端分别开有取压孔。本发明基于CFD仿真设计了新型差压式微小流量计,研究了新型差压式流量计各个结构参数对测量性能的影响,并选取最优的结构参数,制成实验样机,其中最优模型在流量点240mL/h～400mL/h内的仪表系数线性度误差达到了1.9％,最终使得流量计测量流量下限达到了10mL/h,满足对微小流量的测量要求。(The invention provides a differential pressure flowmeter and a measuring method for measuring micro flow. The differential pressure flowmeter adopts a spiral pipe as a test pipe section for micro fluid flow, two ends of the spiral pipe are respectively connected with a pipeline with the inner diameter larger than the inner diameter of the spiral pipe through a reducing clamping sleeve, and two ends of the spiral pipe are respectively provided with a pressure taking hole. The invention designs a novel differential pressure type micro flow meter based on CFD simulation, researches the influence of each structural parameter of the novel differential pressure type flow meter on the measurement performance, selects the optimal structural parameter and manufactures an experimental prototype, wherein the instrument coefficient linearity error of the optimal model in a flow point of 240-400 mL/h reaches 1.9 percent, finally the lower limit of the flow measured by the flow meter reaches 10mL/h, and the measurement requirement on the micro flow is met.)

1. A differential pressure flowmeter for measuring micro flow is characterized by comprising a spiral pipe used as a fluid flow testing pipe section, wherein two ends of the spiral pipe are respectively connected with a pipeline with an inner diameter larger than the inner diameter of the spiral pipe through a reducing clamping sleeve, and a pressure taking hole is formed in the pipeline.

2. The differential pressure flowmeter for measuring a minute flow rate according to claim 1, wherein an inner diameter of the spiral tube is 0.6mm to 1 mm.

3. The differential pressure flowmeter for measuring a minute flow rate according to claim 1, wherein the diameter of the pipe in which the spiral pipe is wound is 20mm to 100 mm.

4. The differential pressure flow meter for measuring minute flows according to claim 1, wherein the spiral tube is wound for 8 to 20 turns.

5. The differential pressure flowmeter for measuring a minute flow according to claim 1, wherein two straight pipe sections are respectively extended from both ends of the spiral pipe, the two straight pipe sections extended from both ends of the spiral pipe are respectively connected to a first large-diameter pipe through a first variable diameter ferrule, the two first large-diameter pipes are respectively connected to a second large-diameter pipe through a second variable diameter ferrule, and an inner diameter of the first large-diameter pipe is larger than an inner diameter of the spiral pipe and smaller than an inner diameter of the second large-diameter pipe; and the two pressure taking holes are respectively formed in the second large-caliber pipeline.

6. The differential pressure flowmeter for measuring a minute flow rate according to claim 5, wherein an inner diameter of the first large diameter pipe is 4mm, and an inner diameter of the second large diameter pipe is 10 mm.

7. The differential pressure flowmeter for measuring a minute flow according to claim 6, wherein a pressure taking hole at an inlet is 150mm from the orifice of the second large diameter pipe, and a pressure taking hole at an outlet is 50mm from the orifice of the second large diameter pipe.

8. The differential pressure flow meter for measuring a minute flow rate according to claim 1, wherein the minute flow rate measured by the differential pressure flow meter is a flow rate of 10mL/h to 600 mL/h.

9. A measuring method for measuring micro flow is characterized by comprising the following steps:

a. the method comprises the following steps that a spiral pipe is used as a test pipe section of micro fluid flow, two ends of the spiral pipe are respectively connected with a pipeline with the inner diameter larger than the inner diameter of the spiral pipe through a reducing clamping sleeve, and two pressure taking holes are formed in the pipeline;

b. collecting differential pressure delta P at an inlet and an outlet of a pipeline through two pressure taking holes;

c. the flow rate Q of the minute fluid flowing through the spiral tube is calculated according to the following formula:

wherein D is the inner diameter of the spiral tube, L is the length of the spiral tube, and μ is the dynamic viscosity of the fluid.

10. The method as claimed in claim 9, wherein the inner diameter of the spiral tube in the step a is 0.6mm to 1 mm.

Technical Field

The invention relates to the technical field of flow detection, in particular to a differential pressure flowmeter and a measuring method for measuring micro flow.

Background

At present, instruments for measuring a minute flow rate mainly include a vane wheel type flowmeter, a positive displacement flowmeter, a float type flowmeter, an ultrasonic flowmeter, and the like.

The impeller type flowmeter has the working principle that an impeller is placed in a measured fluid, the impeller is impacted by the fluid flow to rotate, and the rotation speed of the impeller reflects the flow. Typical impeller-type flow meters are water meters and turbine flow meters, which may be configured in either a mechanical drive output or an electrical pulse output. The disadvantages are: the inability to maintain calibration characteristics over time; the physical properties of the fluid have a large influence on the flow characteristics.

The measurement principle of the positive displacement flowmeter is as follows: when fluid passes through the flowmeter, a certain pressure difference is generated between an inlet and an outlet of the flowmeter, a rotating part (called a rotor for short) of the flowmeter rotates under the action of the pressure difference, and the fluid is discharged from the inlet to the outlet, and in the process, the fluid fills a metering space of the flowmeter once and again and then is continuously sent to the outlet. The volume of the metering space is determined for a given flow meter condition, and a cumulative value of the volume of fluid passing through the flow meter is obtained as long as the number of revolutions of the rotor is measured. But the structure is complex, the volume is huge, the device is not suitable for the occasions of high and low temperature, and the noise and the vibration are large.

The measurement principle of the float-type flowmeter is as follows: when the measured fluid passes through the annular gap formed by the taper pipe and the floater from bottom to top, differential pressure is generated at the upper end and the lower end of the floater to form the rising force of the floater, when the rising force borne by the floater is larger than the weight of the floater immersed in the fluid, the floater rises, the area of the annular gap is increased, the flow rate of the fluid at the annular gap is immediately reduced, the differential pressure at the upper end and the lower end of the floater is reduced, the rising force acting on the floater is reduced, and the floater is stabilized at a certain height until the rising force is equal to the weight of the floater immersed in the fluid. The height of the float in the taper pipe corresponds to the flow passing through. Although the float flowmeter has a simple structure, only pure water can be measured, and the flow value can be read only by human eyes, the measurement accuracy is low, and the float flowmeter is not suitable for accurate measurement of micro flow.

The measurement principle of the ultrasonic flowmeter is as follows: since the ultrasonic waves carry information on the flow velocity of the fluid when propagating through the flowing fluid, the flow velocity of the fluid can be detected by the received ultrasonic waves and converted into a flow rate. The ultrasonic flowmeter obtains the flow velocity of the fluid by receiving and processing ultrasonic signals passing through the fluid, can realize non-contact measurement and is not influenced by the self factors of the fluid. However, at ultra-low flow, the experimental pipeline is too small to install the ultrasonic receiver and the ultrasonic generator, and clutter may be generated during the test process, which causes the pipeline fluctuation, and thus the micro flow cannot be accurately measured. Ultrasonic flow meters are also more expensive than other flow meters.

At present, the types of micro flowmeters used in industry are not many, most of the micro flowmeters are in a laboratory stage, and the current micro flowmeters have the problems of low lower flow limit, low measurement accuracy and the like, so that the research on the micro flowmeters is necessary.

Disclosure of Invention

The invention aims to provide a differential pressure flowmeter and a measuring method for measuring micro flow so as to realize accurate measurement of the micro flow.

The invention is realized by the following steps: a differential pressure flowmeter for measuring micro flow rate adopts a spiral pipe as a test pipe section of the micro flow rate, two ends of the spiral pipe are respectively connected with a pipeline with an inner diameter larger than the inner diameter of the spiral pipe through a reducing clamping sleeve, and pressure taking holes are respectively arranged on the pipelines at two ends of the spiral pipe. The minute flow referred to in the present invention means a flow rate of 10mL/h to 600 mL/h.

Preferably, the inner diameter of the spiral pipe is 0.6mm-1 mm.

Preferably, the diameter of the pipe formed by coiling the spiral pipe is 20mm-100 mm.

Preferably, the number of turns of the spiral pipe is 8-20.

Preferably, two straight tube sections are respectively extended from two ends of the spiral tube and connected with the diameter-changing clamping sleeve, specifically, the two straight tube sections extended from the two ends of the spiral tube are respectively connected with the first large-diameter tube through the first diameter-changing clamping sleeve, the two first large-diameter tubes are respectively connected with the second large-diameter tube through the second diameter-changing clamping sleeve, and the inner diameter of the first large-diameter tube is larger than that of the spiral tube and smaller than that of the second large-diameter tube. And the two pressure taking holes are respectively formed in the second large-caliber pipeline.

Preferably, the first large-diameter pipe has an inner diameter of 4mm, and the second large-diameter pipe has an inner diameter of 10 mm. The pressure taking hole at the inlet is 150mm away from the pipe orifice of the second large-caliber pipe, and the pressure taking hole at the outlet is 50mm away from the pipe orifice of the second large-caliber pipe.

The measuring method for measuring a minute flow rate corresponding to the differential pressure flowmeter includes the steps of:

a. the method comprises the following steps that a spiral pipe is used as a test pipe section of micro fluid flow, two ends of the spiral pipe are respectively connected with a pipeline with the inner diameter larger than the inner diameter of the spiral pipe through a reducing clamping sleeve, and two pressure taking holes are formed in the pipeline;

b. collecting differential pressure delta P at an inlet and an outlet of a pipeline through two pressure taking holes;

c. the flow rate Q of the minute fluid flowing through the spiral tube is calculated according to the following formula:

wherein D is the inner diameter of the spiral tube, L is the length of the spiral tube, and μ is the dynamic viscosity of the fluid.

The invention aims to design a special flowmeter, design a novel differential pressure type micro flowmeter based on CFD simulation, study the influence of each structural parameter of the novel differential pressure type flowmeter on the measurement performance, select the optimal structural parameter and manufacture an experimental prototype, wherein the instrument coefficient linearity error of the optimal model in a flow point of 240 mL/h-400 mL/h reaches 1.9%, finally the lower limit of the flow measured by the flowmeter reaches 10mL/h, and the measurement requirement on the micro flow is met.

Drawings

Fig. 1 is a schematic view of a differential pressure flowmeter according to the present invention.

Fig. 2 is a schematic view of the construction of the spiral duct of fig. 1.

FIG. 3 is a schematic diagram of the relationship between the flow rate and the differential pressure of six spiral pipe models obtained under different inner diameters of the spiral pipes in the CFD simulation.

FIG. 4 is a schematic diagram of the flow versus differential pressure relationship for six types of spiral pipe models obtained for different diameters of the spiral pipe coiled tubing using CFD simulation of the present invention.

FIG. 5 is a schematic diagram showing the relationship between flow and differential pressure of six types of spiral pipe models obtained under different spiral pipe coiling heights in the CFD simulation of the present invention.

FIG. 6 is a schematic diagram showing the relationship between the flow rate and the differential pressure of six spiral pipe models obtained under different numbers of turns of the spiral pipe when CFD simulation is adopted in the present invention.

FIG. 7 is a schematic diagram showing the relationship between the flow rate and the differential pressure obtained by continuously measuring 3 times at 13 flow rate points by using the experimental prototype No. 1-3 according to the present invention.

Fig. 8 is a schematic diagram showing the relationship between the flow rate and the differential pressure obtained by continuously measuring 3 times at 13 flow rate points by using experimental prototypes No. 3 and No. 4 according to the present invention.

FIG. 9 is a graph showing the relationship between the flow rate and the differential pressure obtained by continuously measuring 3 times at 13 flow rate points using the experimental prototype Nos. 4 and 5 according to the present invention.

FIG. 10 is a graph comparing data obtained using CFD simulation of the present invention with experimental prototypes.

FIG. 11 is a schematic view of a fitting curve of the flow rate and the differential pressure obtained by linear fitting of the experimental prototype No. 1 according to the present invention.

FIG. 12 is a graph showing a fitting curve of the flow rate and the differential pressure obtained by linear fitting of the experimental prototype No. 2 according to the present invention.

FIG. 13 is a schematic view of a fitting curve of the flow rate and the differential pressure obtained by linear fitting of the experimental prototype No. 3 according to the present invention.

FIG. 14 is a graph showing a fitting curve of the flow rate and the differential pressure obtained by linear fitting of the present invention to the experimental prototype No. 4.

Detailed Description

The invention aims to improve the precision of the flowmeter in measuring micro flow and the lower limit of the flow, researches the influence of the structural parameters of the differential pressure type flowmeter on the measurement result based on the CFD simulation technology, determines a proper micro flow measurement scheme through comparison and analysis, manufactures an experimental prototype of the differential pressure type micro flowmeter, and performs actual flow test. The results show that the experimental data and the CFD simulation result have the same trend.

Specifically, the differential pressure type flowmeter is designed based on CFD simulation by taking the Hargen-Poiseusey law as a principle. And (3) realizing geometric modeling and simulation analysis of the model through CFD (computational fluid dynamics) simulation software, and finally determining the differential pressure type flowmeter test pipe section as a spiral pipe section. Besides the spiral pipe section, the invention also carries out simulation research on the straight pipe section. And drawing a corresponding model design drawing through CFD simulation, measuring a differential pressure value of a pipe section, and researching the relation between the flow value and the differential pressure value. For the straight pipe section model, the whole pressure difference is too small, when a pipeline with a small caliber is adopted, the linear relation between the pressure difference value and the flow rate is gradually deteriorated, and the linearity error of the corresponding instrument coefficient is increased. In addition, in consideration of the practical problems of overlong pipeline of the straight pipe section, large floor area, post processing and manufacturing and the like, the invention does not adopt the straight pipe section model as the differential pressure flowmeter. Therefore, the following experimental prototype did not use a straight tube section. The present invention uses spiral pipe as differential pressure flowmeter. And through the research on the adapter pipe fitting and the pressure measuring position of the differential pressure flowmeter, the differential pressure flowmeter is determined to be used as the flowmeter for measuring the micro flow. And finally, analyzing the influence of the structural parameters of the differential pressure flowmeter on the performance of the measurement result based on CFD simulation, manufacturing differential pressure flowmeters with different structures as experimental prototypes, and performing real-flow test.

According to the Hagen-Poiseue's law, for incompressible fluid, the fluid fully develops laminar flow in a closed pipeline, and when the fluid density and other structural parameters are kept constant, the differential pressure value and the fluid flow velocity are in a linear relation after the fluid flows through a section of pipeline. The fluid flows in from the inlet of the pipeline, fully develops into a laminar flow state in the pipeline and then flows out from the outlet of the pipeline, and the fluid is supposed to be incompressible, and keeps a stable laminar flow state in the pipeline all the way without sliding with the wall surface.

As shown in fig. 1, the differential pressure flowmeter of the present invention includes a spiral pipe 1 (see fig. 2 for specific structure), the spiral pipe 1 is used as a test pipe section of the differential pressure flowmeter, two straight pipe sections extend from two ends of the spiral pipe 1, the two straight pipe sections are respectively connected to a first large-diameter pipe 3 through a first diameter-changing ferrule 2, the first large-diameter pipe 3 is connected to a second large-diameter pipe 5 through a second diameter-changing ferrule 4, and the diameter of the first large-diameter pipe 3 is larger than that of the spiral pipe 1 and smaller than that of the second large-diameter pipe 5. Preferably, the inner diameter of the spiral pipe 1 is 0.6mm, the inner diameter of the first large-diameter pipe 3 is 4mm, and the inner diameter of the second large-diameter pipe 5 is 10 mm. The first reducing cutting sleeve 2 and the second reducing cutting sleeve 4 are composed of a joint body, a front cutting sleeve, a rear cutting sleeve and a screw cap. The first reducing cutting ferrule 2 is very simple and easy to install at two ends of the spiral pipe 1. A first pressure sampling hole 6 and a second pressure sampling hole 7 are respectively formed in the two second large-diameter pipes 5, the first pressure sampling hole 6 is a pressure sampling hole on the inlet end side, and the second pressure sampling hole 7 is a pressure sampling hole on the outlet end side. Preferably, the distance from the first pressure taking hole 6 to the pipe orifice of the second large-caliber pipe 5 is 150mm, and the distance from the second pressure taking hole 7 to the pipe orifice of the second large-caliber pipe 5 is 50mm, so as to ensure that the flow pattern at the pressure taking hole is basically stable.

The fluid flows in from the inlet of the pipeline, fully develops into a laminar state in the spiral pipe and then flows out from the outlet of the pipeline, the fluid is supposed to be incompressible, and the stable laminar state is kept in the spiral pipe all the way without sliding with the wall surface, the length of the spiral pipe is L, and the on-way resistance loss h of the fluid caused by viscous acting force is obtained according to Darcy relation_f：

In the formula: lambda is an on-way resistance coefficient, is related to the roughness of the spiral pipe and is dimensionless; d is the inner diameter of the spiral pipe in mm; l is the length of the laminar flow section of the fluid in the spiral pipe, and the unit is mm; g is the local gravitational acceleration measured in m/s²(ii) a v represents the flow rate in unitsm/s。

The flow characteristics of the fluid in the spiral pipe are determined according to the Reynolds number, when the Reynolds number is less than 2300, the fluid keeps a laminar flow state, and the on-way resistance coefficient is only related to the Reynolds number Re:

when the fluid flows in the spiral tube, the reynolds number Re is:

in the formula: μ is the dynamic viscosity of the fluid, in Pa · s; rho is the density of fluid in the spiral pipe and the unit is kg/m³。

Combining the formulae (1), (2) and (3) to obtain

The flow rate of the fluid flowing through the spiral pipe is Q:

and the differential pressure deltap between the inlet and the outlet of the measuring pipeline is as follows:

ΔP＝h_fρg (6)

the formulas of the differential pressure type flowmeter under the laminar flow state can be obtained by combining the formulas (4), (5) and (6):

according to the formula (7), under the laminar flow state, other parameters keep a certain time, and the flow rate and the differential pressure value are in a direct proportion relation, so that the flow rate value of the fluid flow passing through the spiral pipe can be obtained only by knowing the inner diameter D of the spiral pipe, the length L of the spiral pipe and the differential pressure delta P of the inlet and the outlet of the pipeline in the measurement process.

The fluid can produce the vortex through reducing cutting ferrule department, makes the fluid internal friction effect aggravation, has great mechanical energy to consume, produces pressure loss. The simulated speed cloud chart shows that the flow pattern of the fluid at the outlet is stable at a position which is basically 100mm away from the second reducing cutting sleeve, and in order to ensure that the flow pattern is more stable, a position which is 50mm away from the orifice of the second large-diameter pipe (the pipe length is 200mm) of the pressure taking hole is selected at the outlet; and at the inlet, selecting a position with a pressure measuring hole 150mm away from the orifice of the second large-caliber pipe, and obtaining the differential pressure delta P at two ends of the spiral pipe through the two pressure measuring holes. The reason why pressure is not taken at the two ends of the spiral pipe is that the pressure cannot be taken because the inner diameter of the spiral pipe is too small.

When CFD simulation is adopted, six spiral tube models with the inner diameters (or called calibers) of the spiral tubes of 0.6mm, 1mm, 2mm, 4mm, 6mm and 10mm are set in simulation research with the flow range of 50 mL/h-1200 mL/h. The flow rate versus differential pressure relationships for these six spiral pipe models are shown in FIG. 3. As can be seen from the figure, the flow rate and the differential pressure distribution curve of the six spiral pipe models increase linearly, the differential pressure value of the spiral pipe is reduced along with the increase of the caliber of the spiral pipe, and the differential pressure and the caliber of the pipeline are in inverse proportion.

Aiming at simulation analysis of the diameter of the spiral pipe coiled pipeline, six spiral pipe models with the diameter of the spiral pipe coiled pipeline being 100mm, 60mm, 50mm, 40mm, 30mm and 20mm are set in simulation research with the flow range being 50 mL/h-1200 mL/h. The flow rate versus differential pressure relationship for these six spiral pipe models is shown in FIG. 4. As can be seen from the figure, the flow rate and the differential pressure distribution curve of the six spiral pipe models have a linear increasing trend, and the inlet and outlet differential pressure values of the spiral pipe are increased along with the increase of the diameter of the coiled pipe, because the length of the spiral pipe is increased due to the increase of the diameter of the coiled pipe, the length of the measuring pipe is increased, and the differential pressure value is increased.

Aiming at simulation analysis of the spiral tube coiling height (under the condition that the length of the spiral tube is fixed, the coiling height is changed by tightly coiling or not tightly coiling), six spiral tube models with the spiral tube coiling heights of 4mm, 10mm, 20mm, 30mm, 40mm and 50mm are set in simulation research with the flow range of 50 mL/h-1200 mL/h. The flow rate versus differential pressure relationship for these six spiral pipe models is shown in FIG. 5. It can be seen from the figure that the flow rate and the differential pressure distribution curve of the six spiral pipe models increase linearly, however, the coiling height of the spiral pipe does not change obviously the differential pressure value of the inlet and the outlet, because the height changes, two structural parameters of the caliber size of the spiral pipe and the length size of the pipeline are not changed fundamentally, and it is also proved that the differential pressure value of the pipeline is only related to the two structural parameters of the caliber size of the pipeline and the length of the pipeline in the laminar flow state, therefore, the height of the spiral pipe needs to be coiled tightly for the appearance of the spiral pipe to be attractive.

Aiming at simulation analysis of the number of winding turns of the spiral tube, six spiral tube models are set in the simulation research of which the flow range is 50 mL/h-1200 mL/h, wherein the number of winding turns of the spiral tube is 2, 4, 5, 6, 8 and 10. The flow rate versus differential pressure relationship for these six spiral pipe models is shown in FIG. 6. As can be seen from the figure, the flow rate and the differential pressure distribution curve of the six spiral pipe models have a linear increasing trend, and the differential pressure value is also obviously increased along with the increase of the number of winding turns of the spiral pipe, because the increase of the number of winding turns of the spiral pipe directly influences the length of the pipeline, the direct proportional relation between the differential pressure value of the inlet and the differential pressure value of the outlet of the differential pressure type flowmeter and the length of the pipeline is proved. After the number of winding turns is 8, when the flow point is 50mL/h, the differential pressure value of the inlet and the outlet of the pipeline reaches 5900Pa, and in order to be capable of measuring the pressure loss value between the inlet and the outlet of the pipeline more accurately, a spiral pipe with the number of winding turns being more than 8 turns is selected as a model.

In order to verify a simulation result, the invention designs five experimental prototypes with the following structures, wherein the experimental prototypes all adopt 304 stainless steel as a processing material, the calibers of all spiral pipes in the experimental prototypes are 0.6mm, the calibers of a first large-caliber pipe are 4mm, and the calibers of a second large-caliber pipe are 10 mm. Five experimental prototypes of different spiral tube configurations are shown in table 1 below.

Table 1 experimental prototype with different structure

The five experimental prototype machines with different structures are manufactured based on CFD simulation analysis of the influence of the structural parameters of the differential pressure type flowmeter on the performance of the measurement result. In the experiment, in order to more accurately measure the differential pressure value of an experimental prototype, the caliber of the spiral pipe is 0.6 mm. The spiral pipe needs to be fixed with an adhesive tape to ensure that the pipe does not deform.

A differential pressure type flowmeter experimental prototype is manufactured according to a simulation model, an experiment is carried out on an experimental platform of a micro flow standard device, 13 flow points are taken for testing, the flow points are respectively 600mL/h, 550mL/h, 500mL/h, 450mL/h, 400mL/h, 350mL/h, 300mL/h, 240mL/h, 200mL/h, 150mL/h, 120mL/h, 50mL/h and 10mL/h, and the 13 flow points (the 13 flow points are all micro flow in the invention) are respectively and continuously measured for 3 times. In order to ensure the data accuracy, the indoor temperature is kept at 20-30 ℃ and the relative humidity is kept at 40-50% during the experiment, five experimental prototypes are respectively adopted for the experiment, the measured fluid medium is water, the five experimental prototypes with different structural parameters are sequentially arranged in the detected pipelines at the same position for real flow measurement, the differential pressure value corresponding to each flow point is obtained, and finally, the average differential pressure value, the average instrument coefficient and the linearity error are calculated, wherein the formula is as follows:

meter coefficient for jth test of ith flow point:

K_ij＝ΔP_ij/v_ij (8)

in the formula: delta P_ijThe differential pressure value of the inlet and the outlet of the differential pressure type flowmeter is in Pa; v. of_ijIs the inlet velocity in m/s.

Average meter coefficient for ith flow point:

instrument coefficient linearity error:

in the formula: k_imaxIs the maximum value in the measuring instrument coefficients; k_iminIs the minimum value among the gauge coefficients.

The influence of the spiral tube parameters on the measurement performance is experimentally researched, and the experimental results of three different coiling diameter prototypes at the flow rate of 10mL/h-600mL/h (see fig. 7), two different coiling number prototypes at different flow rates (see fig. 8) and two different coiling height prototypes at different flow rates (see fig. 9) are experimentally researched. As can be seen from FIGS. 7-9, three groups of data of each experimental prototype tested for 3 times continuously are basically overlapped, the differential pressure value of each experimental prototype within the flow rate of 10mL/h-600mL/h and the flow rate are basically in a linear relationship, the experimental result is consistent with the simulation result, and the CFD simulation technology has good reference value for researching the structural parameters of the differential pressure type flowmeter. However, the simulation data and the experimental data have a certain difference, because the simulation model is established in an assumed ideal environment, wherein the influence of gravity and frictional resistance is ignored, so that the simulation model cannot be completely identical to the actual sensor model. As shown in fig. 10, fig. 10 shows the real flow experimental test data compared with the simulation data. Although it can be seen from fig. 10 that the simulation data and the experimental data have a certain difference, the variation trend of the differential pressure data of the experimental prototype is approximately the same as that of the simulation data, and the flow rate and the differential pressure distribution curve increase linearly.

The differential pressure value and the flow of each differential pressure flowmeter in the whole micro flow range are in a linear relation, in order to obtain the linear relation between the flow value and the differential pressure value of each differential pressure flowmeter, each differential pressure flowmeter needs to be subjected to linear fitting to obtain a constant coefficient between the flow and the differential pressure, and finally a fitting model of the differential pressure flowmeter is determined:

y＝ax+b (11)

in the formula: and a and b are constant coefficients of a fitting formula.

Because the height change of the spiral pipe has no great influence on the measurement performance, and the differential pressure values distributed at all flow points are basically the same, the experiment only carries out linear fitting on the differential pressure and the flow of the first 4 prototype machines:

square of correlation coefficient (decision coefficient) R of linear fitting of model No. 1²The fitted curve is shown in fig. 11, and the linearity error of the meter coefficient of this prototype in the flow point range of 240mL/h to 400mL/h is 2.27%.

Square of correlation coefficient (decision coefficient) R of linear fitting of model No. 2²The linearity error of the meter coefficient for this prototype, see figure 12, over flow points 240-400 mL/h is 2.22%, 0.9978.

Square of correlation coefficient (decision coefficient) R of linear fitting of model No. 3²The linearity error of the meter coefficients for this prototype at flow points 240-400 mL/h is 1.9%, as shown in figure 13, fitted to a curve of 0.9958.

Square of correlation coefficient (decision coefficient) R of linear fitting of model No. 4²The linearity error of the meter coefficients for this prototype at flow points 240-400 mL/h is 2.05%, see figure 14, fitted curve 0.9955.

By establishing the models of the first 4 experimental prototypes and analyzing the fitted data, the performance of the experimental prototypes is evaluated by taking the instrument coefficient linearity error as the quality, wherein the optimal structural model is the No. 3 experimental prototype, the instrument coefficient linearity error of the No. 3 experimental prototype reaches 1.9 percent, and the instrument coefficient linearity error is the lowest in all models.