Research On The Geometric Structure Of Pitot Tube By The Wind Tunnel Test

The accuracy of carbon dioxide and other greenhouse gas emissions data is not only related to the implementation of the state related emission reduction control indicators,but also whether a country is true to achieve greenhouse gas emission reduction commitments and the fairness of carbon trading within the country.According to the statistics,in our country,carbon dioxide emission through the flue exhaust(hereinafter referred to as flue gas)into the atmosphere accounting for more than 75% of the country's total emissions.Therefore,accurate measurement of greenhouse gas emissions in the flue gas is crucial.The accuracy of measurement of greenhouse gas concentration in flue gas is high.The main source of uncertainty comes from the uncertainty of flue gas flow measurement.The S type pitot tube is not easily blocked,easy to be installed and maintained,because of its large caliber.Usually,S type skin trustee is used as the main instrument for flue gas measurement in industry.Currently,the accuracy of measurement of greenhouse gas concentrations in the flue gas is very high,so the main sources of uncertainty comes from the flue gas flow measurement uncertainty.S-type Pitot tube due to the large diameter easy to plug,easy installation and maintenance features are widely used in the flue gas and other high temperature,high humidity,high corrosion,dust,high dielectric turbulence measurements.EPA method 2 by the U.S.Environmental Protection Agency identified S-type Pitot tube as the standard instrument of flue gas measurement.Method 2 assumes calibration factor S-type Pitot tube was 0.84 and constant or calibrated in the low-turbulence wind tunnel without angle of deflection.But the study found that the actual correction coefficient of S-type Pitot tube is related to the flow velocity,angle of deflection.Transverse flow also has great impact on the calibration factor of S-type Pitot tube.Based on the large diameter flue gas flow simulation wind tunnel device,the influence of different forms of pitot tube on calibration coefficient is studied in this paper.At the beginning of 2017,Chinese Institute of Metrology established a set of large calibre gas flow simulation wind tunnel.The device uses the Laser doppler velocimeter("LDV")measuring system as the original level standard,and then passes the velocity value to the Pitot tube respectively,and transfers the flow value to the flowsic 600 ultrasonic flowmeter.The fan,as the power source of the device,has studied the stability of the flow in the opening mode of the three types of blower,and determines the opening mode of the fan which makes the flow of the test section most stable-the single blower A as the power source of the pitot tube test.Secondly,the uncertainty of the calibration coefficient of the conventional S type pitot tube is evaluated under the device.The uncertainty is 0.37%.Based on the test capability of the large caliber wind tunnel standard device,7 conventional S model and 5 rhombus mop models are selected.The influence of the geometric structure of the skin trusteeship on the calibration coefficient is studied in the range of 1 ~ 30m/s,the results show that:(1)For the conventional S type,the change of the distance between the total and the static pressure holes and the inner diameter of the tube has a certain influence on the calibration coefficient,and the radius of curvature of the tube has no effect on the calibration coefficient.When the hole distance shrinkage,the value of the calibration coefficient becomes smaller and more consistent,the differential pressure between the total and the static pressure holes becomes larger.When the inner diameter of the tube is reduced,the value of the calibration coefficient becomes smaller and the consistency becomes worse,and the differential pressure between the total and the static holes becomes larger.(2)For rhombohedral pitot tube,changing the angle of the total and static pressure hole has a certain effect on the calibration coefficient,and the calibration coefficient increases with the increase of flow rate.When the angle of the inclined surface of the total pressure hole increases,the calibration coefficient becomes smaller and the differential pressure between the static pressure and the total pressure becomes larger.When the angle of the inclined plane of the static pressure hole increases,the calibration coefficient becomes smaller and then becomes larger.The corresponding pressure coefficient of the differential pressure decreases first and then becomes smaller,and the pressure of the static pressure hole becomes smaller then and then becomes larger.(3)It is easy to find out that the two types of S skin trusteeship between conventional and rhombus types are easy to find.The influence of the conventional skin trusteeship and rhombic skin trusteeship on the calibration coefficient is good and bad.The uniformity of the calibration coefficient is better than the diamond,and the fluctuation is smaller;the differential pressure of the rhombus tubing is greater than that of the conventional skins,with higher sensitivity and wider range of velocity measurement.