CN101140162A - Method for measuring flow area of hole with complex profile by supercritical pressure ratio - Google Patents
Method for measuring flow area of hole with complex profile by supercritical pressure ratio Download PDFInfo
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Abstract
The invention discloses a method for measuring the flow area of a complex profile hole, which mainly comprises the following steps: air pressure P in front of the profile hole of the workpiece to be measured1 *Adjusting to supercritical pressure ratio, i.e. not less than 2 times atmospheric pressure PoEnsuring that the air passes through the profile holes at a critical velocity and then expands further to be exhausted to the atmosphere through the exhaust duct. Measuring the air pressure P in front of the profile hole1 *Air temperature T1 *And the air flow Ga passing through the pipeline, the coefficient m of the air is calculated by the air adiabatic index K and the gas constant R, and the data are substituted into the flow equation of the compressible flow to calculate the flow area of the tested complex-shaped surface hole. Compared with the prior art which utilizes the aerodynamic force to measure the area of the profile hole, the method for measuring the flow area of the complex profile hole by the supercritical pressure ratio disclosed by the invention has the advantages of high measurement precision, large measurement range, strong universality of a measuring device, convenience in operation and the like, and solves the problem of accurate measurement of the flow area of the complex profile hole with a small flow area.
Description
Technical Field
The invention relates to a method for measuring the flow area of a molded surface hole, in particular to a method for accurately measuring the flow area of an irregular complex molded surface hole by using aerodynamic force.
Background
The existing method for measuring the flow area of the molded surface hole by using aerodynamic force adopts a method far lower than a critical ratio to enable air to flow through the molded surface hole at a low speed, at the moment, the flow of the air is close to incompressible flow, the Reynolds number of the air flowing in a pipeline is kept to be larger than 3150, namely, the viscous influence of the air is also small enough, and a basic formula of the design calculation can be represented by the following formula:
the air flow rate Ga (kg/s) through the profile holes is:
the flow area of the profile holes is therefore:
wherein: ga-air flow through profile hole (Kg/s)
F Model (III) Area of profile hole (m) 2 )
C-efflux coefficient
Beta-shrinkage, D/D for round holes
D-diameter of pipe
Delta P-pressure differential (Pa) across the orifice
Coefficient of expansion of epsilon-air
Rho-air Density (Kg/m) 3 )
Wherein: c = f (ReD, beta) ReD-Reynolds number of gas flow in tube
ε＝f(P 0 /P 1 ，β，)
P 1 Measuring air pressure (Pa) in front of the profile hole
P 0 -measuring the air pressure (Pa) in the exhaust pipe after the profile hole, which is equal to the atmospheric pressure.
The analysis of the calculation formulas shows that the characteristics are as follows:
1. in the basic formula of the calculation, air is assumed to be incompressible flow, and the calculation is performed without viscosity to simplify the formula.
2. And three parameters of C, beta and epsilon are used for correcting in order to reduce errors, and mainly errors caused by compressibility of air and viscosity of the air are corrected.
3. Measuring the area F of the profile hole Model (III) In the above formula, ga can be measured, because there is no shunt or leakage in the pipeline, according to the principle of continuity of airflow, the airflow in the whole pipeline is equal, the airflow Ga can be measured only by a standard orifice plate, the rest parameters Δ P can be measured, ρ can be calculated from the measured air state parameters temperature and pressure, and as for the three parameters C, β, and ∈, the three parameters C, β, and ∈canbe obtained through a large amount of test data and curves for a simple regular profile hole, and as for a complex profile, the three parameters C, β, and ∈cannotbe obtained. Therefore, the measurement method can only obtain the area of the holes relative to the comparative similar molded surface, is a relative value, and cannot obtain an exact numerical value of the flow area.
The characteristics of this measurement method determine the limitations of its range of use and its error.
1. A small flow restriction. In order to prevent the error caused by the air viscosity at the time of small flow rate from being too large, the reynolds number in the specified fluid pipeline must be larger than 3150, the diameter of the pipeline must be larger than phi 50, and the area of a complicated surface hole is usually relatively small in engineering, so that the measurement method falls within a limited range. Some are within the allowable range, but are close to the limit line, and the error is large.
2. Flow rate limitation in the pipe. In order to reduce the error caused by air expansibility, the flow rate of air in the pipeline is required not to be too high, and the specific requirement is Po/P 1 * > 0.75, i.e. Δ P < 0.33Po, otherwise the error due to air expandability would be too large.
3. The measuring device designed by the method has poor universality. Because the measuring method is limited by small flow and large flow velocity, one device can only measure a small-range flow area, and therefore the universality is poor.
4. The measurement error is large. Due to the influence of air expansibility and viscosity, the measurement result is also influenced by the change of atmospheric pressure.
5. The measurement result can only compare the relative area, and the value of the specific area cannot be obtained.
Disclosure of Invention
Aiming at the defects of the method for measuring the flow area of the profile hole by using aerodynamic force in the prior art, the invention aims to provide a method for measuring the flow area of the complex profile hole by using the supercritical pressure ratio, so as to solve the problems of large measurement error, small measurement range, poor universality of a measuring device, incapability of accurately measuring the small complex profile hole and the like in the prior art.
The above problems to be solved by the present invention can be achieved by adopting the following technical solutions.
The design and calculation of the air as compressible flow, i.e. the air is considered as compressible flow, and the design and calculation of the measuring method is performed as compressible flow.
2 keeping the measuring profile Kong Qiande air pressure P during measuring 1 * To atmospheric pressure P o Is greater than the critical pressure ratio to ensure that air can pass through the profiled orifice being measured at a critical velocity. Critical pressure for airForce ratio is Plin/P 1 * =0.5283, so P is typically required 1 * ≥2P 0 I.e. require P 1 * Greater than or equal to 2 times atmospheric pressure. Because of the convergent channel, the air flow passes through the tested profile hole at critical speed, and the pressure is further reduced to be close to the atmospheric pressure in the pipeline through expansion waves and is discharged into the atmosphere.
3 measuring the air pressure P in the pipeline 1 * Temperature T 1 * And a flow rate Ga.
4 according to the measured pressure P 1 * Temperature T 1 * And the flow Ga calculates the area F of the measured profile hole Model (II) 。
Area F of measured profile hole Model (III) The following formula is preferably selected for calculation:
in order to obtain better technical effects, the invention also adopts the following technical measures:
arranging a straight pipe with the length not less than 10 times of the diameter D of the pipeline in front of an orifice plate for measuring the flow Ga, so that the air flow stably and uniformly flows through an orifice of the orifice plate;
reducing the pressure of the air flowing through the tested hole to be slightly greater than the atmospheric pressure through the expansion wave:
by varying the profile Kong Qiande air pressure P 1 * Changing the profile hole flow area F Model (III) By setting different P 1 * The value of the method enables the same equipment to measure complex profile holes with different areas, namely the flow area F of the profile hole is enlarged Model (II) And maintaining the optimum measurement accuracy.
The basic design and calculation formula adopted by the invention is as follows:
the flow rate Ga (kg/s) of the gas flow when it flows through the profile hole under test at critical velocity is:
wherein
P 1 * Profile Kong Qiande total gas pressure (Pa)
q (λ) -flow coefficient of gas, λ =1,q (λ) =1 at critical flow rate
T 1 * -total temperature (K) of gas in front of the measured profile hole
Adiabatic index of k-gas
R-gas constant
K = 1.4R = 287.04J/K.kg for air
m＝0.04042
Wherein P is 1 * 、T 1 * Can be directly measured, ga can be measured by a throttle orifice plate at the front part of the pipeline according to the continuity principle of the air flow, and thus the area F of the measured profile orifice can be calculated Model (III) 。
Compared with the prior art face hole measurement method, the invention has the following outstanding advantages and positive effects in summary.
1. The method of the invention takes air as compressible airflow during design and calculation, eliminates errors caused by air compressibility, passes through the measured molded surface hole at critical speed, has few influence factors and high measurement precision, and is particularly suitable for measuring the area of a complex molded surface hole with high measurement precision requirement.
2. The method can accurately measure the complex profile hole with small area. When the small-area hole is measured by the existing method, the air pressure P in front of the measured profile hole 1 * Can be adjusted within a wide range as long as P is properly increased 1 * The flow rate Ga can be brought within the optimum range of the apparatus for accurate measurement.
3. The area measuring device designed according to the measuring method has strong universality, one device can be used as several devices, the expenditure can be saved, and the trial production period can be accelerated. The measurement range of the whole set of equipment is expanded because it eliminates the limitation of air compressibility and minimizes the influence of air viscosity.
4. The measuring method has good stability. The change of the pressure difference before and after the profile hole and the change of the atmospheric pressure do not influence the test result, thereby ensuring the consistent conclusion of multiple tests.
5. The measuring method can obtain the area of the profile hole through tests, and the existing measuring method can only measure a relative value representing the size of the area.
Drawings
FIG. 1 is a schematic view of a measuring device system embodying the present invention.
Fig. 2 is an enlarged view of a portion a of fig. 1.
In the figure, 1 gas source; 2, a gas storage tank; 3, an air source valve; 4 a pressure reducing valve; 5 a pressure reducing valve; 6, a pressure gauge; 7, adjusting a valve; 8 orifice front pressure gauge; 9 a throttle orifice plate; a differential pressure meter before and after the 10-hole plate; 11 pressure gauge before the part to be measured (display P) 1 * ) (ii) a 12, a tested part; 13 Profile hole to be measured (area F) Model (III) ) (ii) a 14 test section; 15 an exhaust pipe; 16 thermometer (display T) 1 * ) (ii) a 17 mounting edges.
Detailed Description
A part to be measured with a complicated surface hole is installed in the measuring device in the manner shown in FIGS. 1 and 2, and the part to be measured 12 is fastened by the mounting edge 17, taking care not to allow air leakage. Compressed air enters an air storage tank 2 from an air source 1, the compressed air has the functions of stabilizing air pressure and removing moisture and impurities in the air, and then air flow enters an air pipeline through an air source valve 3 and passes through a constant pressure reducing valve 4 to reduce the air pressure to a set value. The pressure gauge 6 displays the pressure behind the first-stage constant pressure reducing valve, and then the pressure gauge 11 in front of the part to be measured is accurately adjusted to a set value P1 through the second-stage constant pressure reducing valve 5 and the adjusting valve 7 * While the temperature T of the air flow is displayed by the thermometer 16 1 * The air flow passes through the orifice plate 9 and the differential pressure meter displays the differential pressure before and after the orifice plate. Due to the requirement of the orifice plate 9, a straight line segment with the diameter D20 times of that of the pipe is arranged in front of the orifice plate, so that the airflow is more stable and uniform, the measurement accuracy is ensured, then the airflow enters the part 12 to be measured and passes through the complex profile hole 13 on the part to be measured at the critical speed, and the pressure of the gas from the profile hole is greater than the atmospheric pressure P 0 In the test section 14, the air is reduced in pressure by the expansion wave to a pressure slightly greater than atmospheric pressure and is discharged into the atmosphere through the exhaust pipe 15.
Ga is thus measured by the throttle device, and directly measured P1 * And T 1 * Using the formula set forth above, F can be calculated Model (III) The values can also be read directly by inputting these signals directly into a computer Model (III) The value is obtained.
Claims (8)
1. A method for measuring the flow area of a hole with a complex profile by using a supercritical pressure ratio is characterized by comprising the following steps:
(1) Designing and calculating air according to compressible flow;
(2) Maintaining measurement profile Kong Qiande air pressure P 1 * To atmospheric pressure P o Is greater than the critical pressure ratio to ensure that the air flow is equal toThe critical speed passes through the molded surface hole to be measured;
(3) Measuring the air pressure P in the pipe 1 * Temperature T 1 * And a flow rate Ga;
(4) According to the measured pressure P 1 * Temperature T 1 * And the flow Ga calculates the area F of the measured profile hole Model (III) 。
2. The method of claim 1 wherein the measured profile hole area F is calculated by the following formula Model (III) ：
3. The method for measuring the flow area of a hole with a complex profile according to the supercritical pressure ratio as claimed in claim 1 or 2, characterized in that a straight pipe with the length not less than 10 times of the diameter D of the pipeline is arranged in front of the orifice plate for measuring the flow rate Ga, so that the gas flow can smoothly and uniformly flow through the orifice plate orifice.
4. The method for supercritical pressure ratio measurement of the flow area of a hole with a complex profile according to claim 1 or 2, characterized in that the air flowing through the hole to be measured is reduced to a pressure slightly greater than atmospheric pressure by the pressure of the expansion wave.
5. The method of supercritical pressure ratio measurement of the flow area of a hole with a complicated profile according to claim 3, characterized in that the air flowing through the hole to be measured is reduced to a pressure slightly greater than atmospheric pressure by the pressure of the expansion wave
6. Method for supercritical pressure ratio measurement of the flow area of complex profile holes according to claim 1 or 2, characterised in that the air pressure P is varied on the same set of measuring equipment 1 * Extended measurement typeArea of face flow F Model (III) In the above range.
7. Method for supercritical pressure ratio measurement of the flow area of complex profile holes according to claim 3, characterised in that the air pressure P is varied on the same set of measuring equipment 1 * Enlarging the measured profile hole flow area F Model (III) In the above range.
8. Method for measuring the hole flow area of a complex profile according to the supercritical pressure ratio of claim 4, characterized in that the air pressure P is varied in the same set of measuring equipment 1 * Enlarging the measured profile hole flow area F Model (III) In the above range.
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106680043A (en) * | 2016-11-21 | 2017-05-17 | 北京蓝色星语科技有限公司 | Disturbance sampling device and disturbance sampling method of biochemical harmful factors |
| CN109974634A (en) * | 2019-03-25 | 2019-07-05 | 湖南工业大学 | The test method and test macro of special-shaped structural part throat opening area or flow of media area |
| CN110287572A (en) * | 2019-06-19 | 2019-09-27 | 青岛畅隆电力设备有限公司 | A kind of design method of orifice-plate type drain valve valve plate throttle orifice |
| CN110333145A (en) * | 2019-07-15 | 2019-10-15 | 苏州热工研究院有限公司 | Microspecimen High temperature bulging test device and test method |
| CN111665184A (en) * | 2020-07-01 | 2020-09-15 | 中国航空工业集团公司北京长城计量测试技术研究所 | Medicine package positive sample micropore measuring device |
| CN112066938A (en) * | 2020-08-31 | 2020-12-11 | 重庆长安汽车股份有限公司 | Method for measuring effective area of through opening |
| CN112815173A (en) * | 2020-12-29 | 2021-05-18 | 上海空间推进研究所 | System and method for predicting throttle area of throttle orifice plate |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN2199525Y (en) * | 1994-01-06 | 1995-05-31 | 中国建筑材料科学研究院水泥科学研究所 | Measurer for specific surface of granular material |
| GB9805422D0 (en) * | 1998-03-13 | 1998-05-06 | Standard Aero Limited | Gas flow area measurement |
| CN1333238C (en) * | 2005-05-20 | 2007-08-22 | 中国科学院力学研究所 | Method for measuring supercritical state aviation kerosene discharge |
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- 2007-10-15 CN CNB2007100502313A patent/CN100567890C/en not_active Expired - Fee Related
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| CN106680043A (en) * | 2016-11-21 | 2017-05-17 | 北京蓝色星语科技有限公司 | Disturbance sampling device and disturbance sampling method of biochemical harmful factors |
| CN109974634A (en) * | 2019-03-25 | 2019-07-05 | 湖南工业大学 | The test method and test macro of special-shaped structural part throat opening area or flow of media area |
| CN109974634B (en) * | 2019-03-25 | 2021-05-07 | 湖南工业大学 | Method for testing throat area or medium flow area of special-shaped structural part |
| CN110287572A (en) * | 2019-06-19 | 2019-09-27 | 青岛畅隆电力设备有限公司 | A kind of design method of orifice-plate type drain valve valve plate throttle orifice |
| CN110287572B (en) * | 2019-06-19 | 2023-09-15 | 青岛畅隆电力设备有限公司 | Design method of valve plate orifice for orifice plate type drain valve |
| CN110333145A (en) * | 2019-07-15 | 2019-10-15 | 苏州热工研究院有限公司 | Microspecimen High temperature bulging test device and test method |
| CN110333145B (en) * | 2019-07-15 | 2022-04-01 | 苏州热工研究院有限公司 | High-temperature bulging test device and method for miniature sample |
| CN111665184A (en) * | 2020-07-01 | 2020-09-15 | 中国航空工业集团公司北京长城计量测试技术研究所 | Medicine package positive sample micropore measuring device |
| CN112066938A (en) * | 2020-08-31 | 2020-12-11 | 重庆长安汽车股份有限公司 | Method for measuring effective area of through opening |
| CN112815173A (en) * | 2020-12-29 | 2021-05-18 | 上海空间推进研究所 | System and method for predicting throttle area of throttle orifice plate |
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