Calculation of the Pitot tube correction factor for Newtonian and non-Newtonian fluids

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.     

A Pitot tube system for obtaining water velocity profiles with millimeter resolution in devices with limited optical access

An automated, miniature, S-type Pitot tube system was created to obtain fluid velocity profiles at low flows in equipment having limited optical access, which prevents the use of standard imaging techniques. Calibration of this non-standard Pitot tube at small differential pressures with a custom, low-pressure system is also described. Application of this system to a vertical, high-pressure, water tunnel facility (HWTF) is presented. The HWTF uses static flow conditioning elements to stabilize individual gaseous, liquid, or solid particles with water for optical viewing. Stabilization of these particles in the viewing section of the HWTF requires a specific flow field, created by a combination of a radially expanding test section and a special flow conditioner located upstream of the test section. Analysis of the conditioned flow field in the viewing section of the HWTF required measurements across its diameter at three locations at 1 mm spatial resolution. The custom S-type Pitot tube system resolved pressure differences of <100 Pa created by water flowing at 5–30 cm/s while providing a relatively low response time of ~300 s despite the small diameter (<1 mm) and long length (340 mm) of the Pitot tube needed to fit the HWTF geometry. Particle imaging velocimetry measurements in the central, viewable part of the HWTF confirmed the Pitot tube measurements in this region.     

光电非接触式表面流速测量

针对水工物理模型试验中尚无简单易行的表面流速测量方法,提出了一种新型光电非接触式表面流速直接测量法。在对光束入射水体后散射光强度公式进行推导的基础上,根据水体浅层泥沙浓度的统计继承效应,得出了经上下游浅层泥沙调制的散射光强成相关特性的结论。根据上下游散射光的相关特性,推导了流速测量公式,并分析了上下游测量间距、水流流速、采样率对测量结果的影响。搭建了实验系统,在6种不同标定流速下,分析了不同含沙量对测量精度的影响。实验结果表明,在0～50kg/m36种不同含沙量情况下,实测流速与标定流速的一致性均较好,但水体在10～50kg/m3适量含沙情况下,测量精度较不含沙情况有所提高,测量绝对误差均小于0.1m/s,相对误差能控制在8%以内。     

皮托管在气流测量中一些问题的探讨

皮托管在气流速度测量中受多种因素影响。怎样使测量的数据准确可靠，除了仪器设备外，还要找出影响测量结果的其他原因并对其修正，就显得十分重要。本文的主要目的就是探讨在气流测量中风速的有关修正问题（如水的密度、压力损失、压缩性影响）。以国家气象计量站的设备和测量数据为例，经过水的密度、压力损失、压缩性影响的修正，60m／s时，其修正量为-0．5m／s。这就是为什么在高速时，标准风速偏高的原因。这一结果对于国内国际比对，使气流速度的量值与世界统一具有重要意义。     

Experimental research into a new design of flow-averaging tube

This paper presents the results of investigations into a new design of flow-averaging tube (FAT). The design uses two flow-averaging profiles that affect each other. One of these profiles receives a positive pressure p⁺, and the other a negative pressure p⁻. The differential pressure obtained, , is considerably higher than the differential pressure in other probes on the market. The research reported here aimed to optimize the respective positioning of the profiles. The experiments were performed in an aerodynamic tunnel. Subsequently, tests of prototypes with the profiles were conducted in pipelines with diameters of 104–296 mm. The results are presented in the form of the characteristics of the flow coefficient K as a function of the mean velocity of the air passing through a pipeline. It was found that the new probe design was associated with relatively high measured differential pressures. The observed characteristics are flat over an extensive flow range. This makes it possible to use a constant flow value without degrading the measurement uncertainty.     

The effect of turbulence on a multi-hole Pitot calibration

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.     

Experimental and numerical investigations of the factors affecting the S-type Pitot tube coefficients

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 (Re_D=3.0×10³–2.2×10⁴) had no significant effect on the S-type Pitot tube coefficients.     

基于阵列探头的 PFA 管超声导波流量测量

PFA管材耐腐蚀性好、性能稳定,被广泛应用在半导体等行业的药液运输中,为精确控制药液的用时和用量,需要研究小管径PFA管的非接触式流量测量方法。本文使用超声阵列外卡探头在PFA细管上激励超声导波,并利用导波测量流量。首先比较超声斜探头模态选择和阵列探头模态选择原理的不同,说明阵列探头的频率选择特性,进而设计阵列探头阵元宽度、厚度并制作了三种间距的阵列探头,通过频率扫描得到阵列探头的激励接收特性,比较分析了阵列探头的模态选择效果,并进行了流量测量实验。结果表明阵列探头可增强接收信号强度,提高测量灵敏度,改变阵列间距可以选择不同导波模态,在3 mm PFA管上选择L(0,5)导波模态时流速范围0～6.70 m/s内的测量结果误差限为±0.22 m/s。     

New techniques for multi-component flow velocity measurement using high-frequency pulsed diode lasers

The application of high-frequency pulsed laser diodes for fringe-type laser Doppler anemometry allows multi-component flow velocity measurements by using only one receiver and one signal processing chain. This is effected by synchronization of the laser pulses with the sampling process of the data acquisition system. Consequently, an identical wavelength can be used for all components. The experimental verification of this new technique is described. The technique permits the design of miniaturized and low cost optical flow sensors which can be used for low and high speed flows.     

用于两相流流速测量的极性导向式自适应算法

提出利用导向式自适应算法处理两相流的流动噪声信号,以估计出的流动噪声传输参数计算两相流流速,对这种算法的收敛性和流速测量性能进行了论证.当流动噪声信号量化为1 bit时,则形成极性导向自适应算法,它便于用比较简单的硬件实现快速运算,适于制作成专用的流速检测集成芯片.理论分析和实验结果表明,这种方法测量结果的实时性和分辨率优于相关法.文中给出气水两相流垂直管段与极性相关法进行对比实验的结果.     

Application of averaging bidirectional flow tube for measurement of single-phase flow rate in a piping system

A new instrument, an averaging bidirectional flow tube (BDFT), is proposed to measure single-phase flow rates. This averaging BDFT has unique measuring characteristics foremost among which is the capability to measure bidirectional flow and insensitivity of the fluid attack angle. Single phase calibration tests were conducted to demonstrate the performance of the averaging BDFT. Likewise, to enhance the applicability of the averaging BDFT on various flow conditions, flow analyses using CFD code were performed focusing on design optimization of the BDFT. The calibration test results indicated that this averaging BDFT has a linearity within 0.5 % in the Reynolds (Re) number range of above 10,000 where it is meaningful in terms of application. The flow analyses results demonstrate a good linearity of the averaging BDFT with various design features. Therefore, averaging BDFT can be applied for measurement of flow rates within a wide range of flow conditions. This paper was recommended for publication in revised form by Associate Editor Won-Gu Joo Kyoung-Ho Kang received his B.S. and M. S. degrees in Nuclear Engineering from SNU (Seoul National University), KOREA in 1993 and 1995, respectively. He then received his Ph.D. degree in Nuclear and Quantum Engineering from KAIST (Korea Advanced Institute of Science and Technology) in 2009. Dr. Kang is currently a senior researcher at the Korea Atomic Energy Research Institute in Daejeon, Korea. Dr. Kang’s research interests include analysis and experiments for the nuclear safety, thermal hydraulics, and experiments and modeling for the severe accidents. Byong-Jo Yun received his B.S. degree in Nuclear Engineering from SNU (Seoul National University), KOREA in 1989. He then received his M.S. and Ph.D. degrees from SNU in 1991 and 1996, respectively. Dr. Yun is currently a principal researcher at the Korea Atomic Energy Research Institute in Daejeon, Korea. Dr. Yun’s research interests include analysis and experiments for the nuclear safety, thermal hydraulics, two-phase flow, scaling analysis, and development of instrumentation for two-phase flow. Dong-Jin Euh received his B.S. degree in Nuclear Engineering from Seoul University, Korea, in 1993. He then received his M.S. and Ph.D. degrees from same university in 1995 and 2002, respectively. Dr. Euh is currently a researcher at thermal hydraulic safety research department of Korea Atomic Energy Research Institute in Daejeon, Korea. Dr. Euh’s research interests include two-phase thermal hydraulics in the Nuclear Systems and Fundamental Phenomena. Won-Pil Baek has been working at KAERI as the general project manager (director) for development of nuclear thermalhydraulic experiment and analysis technology since 2001. He received his B.S. degree in nuclear engineering from Seoul National University and his M.S. and Ph.D. degrees from KAIST. In 1991–2000, he worked for KAIST as a researcher and research professor. Currently he also serves as an executive editor of the Nuclear Engineering and Technology, an international journal of the Korean Nuclear Society. His research interests include critical heat flux, integral effect tests, modeling, nuclear safety, and advanced reactor development.     

Examination of disturbed pipe flow and its effects on flow measurement using orifice plates

In a great number of measurements the influence of a disturbed flow on the flow coefficient of a standard orifice plate was investigated. Single bends and double bends out of plane with and without spacer tubes were used as typical disturbances. Experiments were also performed using a combination with a star-shaped flow straightener. The necessary correction factors of the flow coefficient were determined for upstream straight length shorter than detailed in ISO 5167. The flow velocity profiles produced by the disturbances were examined and on this basis profile numbers were calculated. The examinations presented here show that the existing standard should be revised as regards the definition of the fully developed turbulent flow profile and the selection of the required upstream straight lengths.     

皮托静压管的流量测量及不确定度评估

本文介绍了皮托静压管的结构原理及使用场合,讨论了使用皮托静压管进行流量测量时的测量计算方法,分析了实际测量条件下不同因素对流量测量结果的影响,并对测量结果的不确定度进行评估.     

Open channel flow measurement using international standards: introducing a standards programme and selecting a standard

This paper discusses the benefits and practicalities in introducing a standards programme in the field of open channel flow measurement. The work of ISO Technical Committee TC/113 and its subcommittees are discussed and the role of an ISO Technical Report (ISO/TR 8363) in identifying a measurement method is highlighted.     

On the impact of anemometer size on the velocity field in a closed wind tunnel

In the present paper, experimental and numerical investigations of the flow around different types and sizes of anemometers are presented and discussed.The measurements of the flow field at different distances upstream of the anemometer are performed with a laser Doppler Anemometer. The computational results are in good agreement with the experimental ones since the observed deviations are of the same order of magnitude. These results show that anemometers may induce a strong distortion of the velocity field, even far upstream of the anemometer. This distortion has to be taken into account in the anemometer calibration field to yield reliable and consistent measurements.     

Simulation on refrigerant flow in adiabatic capillary tube

This paper proposes a new mathematical model to calculate flow characteristics of the adiabatic capillary tube, which is aimed at solving problems existing in some earlier models. The Stocker’s model was modified with consideration of various effects due to sub-cooling, area concentration, and rolling diameter. The new model can be used not only for R22, but also for its substitutes such as R410A and R407C. A comparison of simulation results of the modified model with those in literature showed that the errors are within 10%. The flow characteristics are finally analyzed. __________ Translated from Journal of hydrodynamics, Ser. A, 2006, 21(3): 318-323 [译自: 水动力学研究与进展]     

薄膜谐振Lamb波传感器测量液体流速矢量的方法

针对液体流速测量领域中微型流量传感器高品质因数、高灵敏度的性能要求。本文设计一种双端增强型薄膜谐振结构实现Lamb波传感器的高品质因数,利用传感器反对称模式(A01模式)在薄膜-液体界面处的消逝波实现液体流速矢量测量。所制作的双端增强型薄膜谐振Lamb传感器A01模式的主峰品质因数为703,A01模式的频率移动量与液体流速大小存在线性关系,频率移动方向与液体流动方向存在对应关系。流速实测灵敏度约为270 Hz/mm/s,传感器稳定性噪声小于0.2Hz,流速最低检测极限值(LOD)为2.2μm/s,流量最低检测极限值(LOD)为18.3nL/min。结果表明,双端增强型薄膜谐振Lamb波传感器可以实现液体流速高灵敏度矢量测量。     

Investigation of the batch measurement errors for single-straight tube Coriolis mass flowmeters

Batch flow is a typical method for calibrating Coriolis flowmeters. It is also an important application for Coriolis flowmeters in the process industry. Batch processes of short duration or from empty have been identified as an important development for Coriolis flowmeters. The measurement of total mass by a commercially available single-straight tube Coriolis flowmeter compared with a weigh scale is presented in this paper. A theoretical understanding for short batch is also provided by numerical simulations of both deterministic and probabilistic parameters. The simulation results agree with the batch tests and may, at least partially, explain the experimental findings.     

基于接触理论的弹簧管刚度测量技术的研究

本文研究了弹簧管头部与夹具孔间的接触变形对弹簧管的刚度测量精度的影响，基于Hertzian接触理论建立了接触模型及其误差分析模型。首先，给出弹簧管刚度测量原理和测量中的受力分析，然后，将测量力引起的接触力简化为均匀线分布后建立接触模型，最终建立测量误差和接触变形的量化关系。通过理论分析和实验验证，接触变形直接降低了测量精确度并增大了测量的不重复性误差。