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1.
Pitot tubes are commonly used to measure gas flow in ducts. The integration of the velocity profile which allows the calculation of the gas flow is described in several international standards such as ISO 3966 or ISO 10780.The common working principle of Pitot tubes is based on the measurement of the differential pressure between the two different pressure taps. The gas velocity is related to this differential pressure through a flow coefficient depending on the Pitot tube type.In case of stable flow, in a pressurized duct, fluctuations of the in-line pressure, even low, can occur. If the response times of the two pressure lines (static and total) between the Pitot tube head and the differential pressure sensor are not equal, these fluctuations can be seen as fluctuations of the measured differential pressure and then of the calculated velocity.This phenomenon is investigated for different design of Pitot tubes and the difference in behaviour of the two pressure lines is highlighted. 相似文献
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Air velocity and flow measurement using a Pitot tube 总被引：3，自引：0，他引：3
Rex Klopfenstein Jr 《ISA transactions》1998,37(4):257-263
The accurate measurement of both air velocity and volumetric airflow can be accomplished using a Pitot tube, a differential pressure transducer, and a computer system which includes the necessary hardware and software to convert the raw transducer signals into the proper engineering units. The incorporation of sensors to measure the air temperature, barometric pressure, and relative humidity can further increase the accuracy of the velocity and flow measurements. The Pitot tube measures air velocity directly by means of a pressure transducer which generates an electrical signal which is proportional to the difference between the pressure generated by the total pressure and the still air (static pressure). The volumetric flow is then calculated by measuring the average velocity of an air stream passing through a passage of a known diameter. When measuring volumetric flow, the ‘passage of a known diameter’ must be designed to reduce air turbulence as the air mass flows over the Pitot tube. Also, the placement of the pitot tube in the passage will influence how accurately the measured flow tracks the actual flow through the passage. Calibrating the measurement system in a wind tunnel can further increase the accuracy of the velocity and the flow measurements. This objective of this paper is to provide the field engineer with single, concise source of information on flow measurement using a Pitot tube. 相似文献
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Calculation of the Pitot tube correction factor for Newtonian and non-Newtonian fluids 总被引：1，自引：0，他引：1
This paper presents the numerical investigation performed to calculate the correction factor for Pitot tubes. The purely viscous non-Newtonian fluids with the power-law model constitutive equation were considered. It was shown that the power-law index, the Reynolds number, and the distance between the impact and static tubes have a major influence on the Pitot tube correction factor. The problem was solved for a wide range of these parameters. It was shown that employing Bernoulli's equation could lead to large errors, which depend on the magnitude of the kinetic energy and energy friction loss terms. A neural network model was used to correlate the correction factor of a Pitot tube as a function of these three parameters. This correlation is valid for most Newtonian, pseudoplastic, and dilatant fluids at low Reynolds number. 相似文献
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National Metrology Institute of Japan (NMIJ) has established a high air speed standard facility and has been providing a calibration service since 2015. The facility has an air speed range of 40 m/s to 90 m/s with a relative expanded uncertainty (k = 2) of 0.63%. The purpose of this primary standard is mainly to contribute to the improvement of meteorological observation research and to the evaluation of flow field inside a turbo machine and around a high speed vehicle. The reference air speed is derived from the national primary gas flowrate standard of Japan. A conversion device from flowrate to air speed is installed in the test line of the closed-loop calibration facility. The reference air speed at the nozzle exit of the conversion device is obtained by comparing the integral of the air speed profiles and the reference volume flowrate. The total pressure tube used as a transfer standard is then calibrated against the reference air speed at the center of the nozzle exit. The Eiffel-type wind tunnel, which is a working standard for the daily calibration service, is calibrated using this total pressure tube. The present paper describes the calibration system, the traceability chain, and an uncertainty analysis using a validation method. 相似文献
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乌石化公司热电厂在瓦斯计量上选用了德国科隆公司生产的涡街流量计VFM5090,介绍仪表选型、测量原理、安装、故障处理等方面内容。 相似文献
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The current study proposes a cost-effective technique wherein a camera can be used anomalously in tandem with the working of a pitot tube in determining the velocity distribution within a boundary layer. The technique involves the traversal of a pitot tube at a uniform velocity inside the width of boundary layer and simultaneously imaging the change in meniscus location of liquid column in the corresponding manometer, inside a wind tunnel set-up. The study aims in establishing a relation between the traversal velocity and the free stream velocity. The proposed approach holds the advantage of providing velocity values at equally spaced locations within the boundary layer, with the number of values depending on the velocity of retraction (traversal away from the surface) as well as the frame rate of recording. Experiments were performed at different combinations of retraction velocity () and Fan Speed for establishing the method. An optimum velocity at which the pitot tube should be retracted was determined based on convergence of trend of the variation in instantaneous meniscus locations to a standard reference trend. Results show that dimensionless optimum velocity () defined as the optimum ratio between tunnel velocity () and is related to the Fan Speed (FS) by FS. Additionally, with regard to the manual traversing performed, the probability density function plots show that traversing manually at introduces higher non-uniformity in the results, thereby preferable to perform the traversal closer to values of . Using the results obtained from the developed imaging technique, the velocity variation within the boundary layer was studied. The technique was successful in precisely locating the prominent points inside a boundary layer for a particular flow condition. Finally as a case study, the imaging approach was also utilized in determining the effect of roughness change across the seam of a cricket ball on its aerodynamics. This case study also shows that the technique is successful in obtaining the flow characteristics of a general boundary layer as well as a flow separation case. 相似文献
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Accurate calibrations of multi-hole Pitot tubes require thousands of measurements spanning ranges of the fluid's velocity, and the pitch and yaw angles. When calibrating a commercially-manufactured multi-hole Pitot tube in NIST's low-turbulence wind tunnel, we found hysteresis in certain ranges of airspeed, pitch angle, and yaw angle. In the worst case, the hysteresis caused a calibration error of 30%. We demonstrate that the hysteresis was caused by a flow instability associated with flow separation. A turbulence intensity of only 1% removes the hysteresis; however, the calibration depends on the turbulence intensity over the entire range of our measurements (0.25–2%). Therefore, multi-hole Pitot tubes should be calibrated and used at the same turbulence levels. 相似文献
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In the monitoring of greenhouse gas emission from industrial smoke-stacks, the most common device used to measure the stack gas velocity is the S-type Pitot tube in South Korea, which is used to estimate the volumetric flow rate by what is termed the Continuous Emission Monitoring System (CEMS). The S-type Pitot tube installed in the stack is inevitably affected during velocity measurements by velocity changes, yaw and pitch angle misalignments due to the harsh environments. Various geometries of the S-type Pitot tube can affect the characteristics of the S-type Pitot tube coefficients, including the degree of sensitivity to velocity changes and yaw and pitch yaw angle misalignments. Nevertheless, there are no detailed guidelines pertaining to the S-type Pitot tube geometry considering accurate and reliable measurements in the ISO, EPA and ASTM international standards. In the present study, S-type Pitot tubes with various geometric parameters, in this case the distance between the impact and wake orifices and the bending angle of the orifices, were manufactured by a 3D printer. Wind tunnel experiments were conducted in the Korea Research Institute of Standards and Science (KRISS) air speed standard system to determine the optimal geometry of an S-type Pitot tube for the accuracy velocity measurements in actual smokestacks which undergo velocity changes and yaw and pitch angle misalignments. Particle image velocimetry was also used to understand the flow phenomena around an S-type Pitot tube under various geometric and misalignment conditions by means of qualitative visualization. The results indicate that S-type Pitot tubes with a long effective length have more constant distributions of the S-type Pitot tube coefficients when the velocity changes from 2 m/s to 15 m/s. The error indexes for yaw angle misalignments show that S-type Pitot tube models with large effective lengths are less affected by yaw angle misalignments. The S-type Pitot tube coefficients were mostly insensitive to the both positive and negative pitch angle misalignments regardless of the velocity and geometry of the various models tested. 相似文献
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在DN25水流量标准装置上对装有梯形漩涡发生体的涡街流量计在低雷诺数下进行试验研究,利用数字信号处理方法(频谱分析方法)得到涡街脱落频率,较传统模拟信号处理方法在保证较好线性度的基础上,有效地扩展了测量下限。绘制雷诺数—仪表系数曲线,发现梯形发生体在低雷诺数下仪表系数K呈递减趋势,当Re>2 000时K趋于常数,这与圆柱发生体在低雷诺数时曲线递增的趋势截然相反。通过分析得知,管道内流速分布的影响、发生体形状的影响和流速与频率关系的影响是导致上述变化趋势的3个主要影响因素。 相似文献
10.
Zhang Haijun;Yang Qin;Zhao Wei;Jiang Feilong; 《Lubrication Science》2024,36(3):231-237
It is very crucial to solve the Reynolds equation quickly and accurately using the numerical methods in the research field of fluid lubrication. For the static Reynolds equation of self-acting gas journal bearings, the typical solution algorithm of the finite difference method is put forward and a new solution algorithm of the finite difference method is proposed. Secondly, the Reynolds equation is solved numerically with the same parameters and the pressure distribution of gas bearings is obtained. Finally, the numerical solution from the new solution algorithm can be obtained with less number of iterations and the less computing time under the different computational grids and bearing numbers. Therefore, the new solution algorithm of the finite difference method is superior to the typical solution algorithm of the finite difference method. 相似文献
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雷诺气体润滑方程仅涉及轴承气膜内的静压分布,对静压气体轴承流道特性的准确刻画还需要研究轴承流道内的气流速度场。将忽略惯性力的纯粘性等温气膜和等熵流动的供气孔拼接,建立了单供气孔环面节流圆盘止推轴承的流道简化模型,给出流道各部分气流马赫数、雷诺数和压力分布的计算公式。结果表明,气膜中气流速度随矢径变化的性质,取决于速度梯度为零的矢径位置;气膜中的气流雷诺数随矢径的增加不断减小。实际的计算结果表明,只要气膜入口截面上的气流马赫数小于临界声速,整个轴承流道将工作在亚音速,供气压力或气膜高度的变化对气膜起始区域边界层发展段长度的影响很小,供气孔始末端截面上压力和温度的变化也很小,忽略惯性力的纯粘性等温雷诺模型基本能够适用轴承的整个亚音速工况。气膜起始区域边界层发展段的长度,可以用气膜中雷诺数大于临界雷诺数的区域长度来近似。 相似文献
12.
In greenhouse gas emission monitoring from industrial stacks, the most common device used to measure stack gas velocity is the S-type Pitot tube. Various factors such as the Reynolds number and misalignment of the installation angle can be additional error sources for the S-type Pitot tube coefficients due to harsh environments. Manufacturing quality of the S-type Pitot tube is also a factor affecting on the measurement uncertainty of stack gas velocity. In the present study, wind tunnel experiments were conducted in Korea Research Institute of Standards and Science (KRISS) standard air speed system to examine the effects of various factors on the S-type Pitot tube coefficients. Numerical simulations were also used to understand flow phenomena around the S-type Pitot tube in the presence of misalignment and distortion of the geometry. The results indicate that misalignment of the pitch and yaw angle change within ±10° changes the S-type Pitot tube coefficients by approximately 2% compared with normal values. The manufacturing quality resulted in unstable values of the coefficients within 2%. However, variations of the Reynolds number (ReD=3.0×103–2.2×104) had no significant effect on the S-type Pitot tube coefficients. 相似文献
13.
The hardware and software of an experimental test system which has been designed, constructed and operated for the analysis of transitional characteristics of a laminar time-dependent flow field into turbulence with comprehensive uncertainty analysis are the major contents of the paper. Therefore presentation herein aims to offer an application case in terms of time-dependent measurement and data acquisition technology using an electronic digital mass flow control (MFC) unit at laboratory site instead of previously used pressure driven mechanisms. The flow field is a sinusoidal pulsatile one in order to simulate the real practice and to utilize the simplicity in production, control and analysis of oscillation. The previous background and the updated portrait on the transitional pulsatile flow [1], [2] are outlined to determine the relevant flow parameters and their critical ranges, the details of the measurement and data acquisition systems and the proposed methodologies. The production of the controlled pulsatile flow and the generated flow characteristics, the methodology for the analysis, accuracy and sensitivity of the measurement and data acquisition chains are given for the purpose. The overall uncertainties of the velocity and pressure measurement chains are found to be ±3.2% and ±1.3%, respectively. The range of the experimental research devised to investigate the interactive influences of oscillation frequency, f and velocity amplitude ratio, A1 in the intermediate and the inertia dominant regions of pulsatile flow field with an emphasis on transition to turbulence is presented via sample measurements of mean velocity and pressure waveforms as solid outputs without going into details on physical aspects of flow dynamics. 相似文献
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ＩＭＰＲＯＶＥＭＥＮＴＳＯＮＴＨＥＣＯＮＦＩＧＵＲＡＴＩＯＮＡＮＤＯＰＴＩＭＵＭＰＡＲＡＭＥＴＥＲＳＯＦＨＩＧＨ一ＳＰＥＥＤＴＨＲＵＳＴＢＥＡＲＩＮＧＳＩＭＰＲＯＶＥＭＥＮＴＳＯＮＴＨＥＣＯＮＦＩＧＵＲＡＴＩＯＮＡＮＤＯＰＴＩＭＵＭＰＡＲＡＭＥＴＥＲ... 相似文献
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针对高转速轴配流中旋转径向小孔出流流量系数开展了实验研究。研究中涉及到两种流动方向,即自旋转缸体中心流过径向小孔向外离心运动称为正向流动,反之则为反向流动。结果表明：旋转小孔出流流量系数同时显著地受离心力和科氏力的影响;因离心力的赋能作用,正向流动时流量系数随转速的增加而变大,反向流动时离心力对小孔内流动有抑制作用,使流量系数随转速的增加而变小;两个方向的科氏力综合效果使正向流动流量系数随出流雷诺数增加而变小,反向流动流量系数随出流雷诺数的增加而变大;当出流雷诺数足够大时,两种流动方向、不同孔型的流量系数各自都有一个稳定值;各种孔型的正向流动流量系数稳定值分布均在0.65～0.80范围内。 相似文献