Comparison of velocity and turbulence profiles downstream of perforated plate flow conditioners

This paper presents the results obtained when placing different designs of perforated plate flow conditioner downstream of two common flow-disturbing installations in turn: a single 90° bend and a twisted S bend. The results comprise a series of LDV measurements of velocity and r.m.s. fluctuation velocity profiles made in two perpendicular planes at locations between 3 and 41 pipe diameters (D) downstream of the conditioners. The flow conditioners were placed at 4D downstream of the flow-disturbing installations. Measurements were also made without the inclusion of a flow conditioner for comparison. Several designs of flow conditioner give profiles within 5% of a fully developed profile 11D downstream of the conditioner; so significant reductions in lengths of meter runs should be possible. The Spearman (NEL) design performs at least as well as other contemporary designs and is available for inclusion in the relevant standards. These measurements were carried out in a water pipeline.     

Influence of upstream disturbances on performance of an LDV-based cryogenic flow meter standard – CFD modelling and preliminary measurements with air

Increasing trade of liquefied natural gas (LNG) imposes stringent requirements for accurate flow rate measurement of this high energy content fluid. To satisfy this demand, a flow meter has been developed by CEASAME Exadebit which is based on velocity measurement behind a contraction nozzle using Laser Doppler Velocimetry technique (LDV). For this instrument, a calibration factor is defined relating the measured velocity to the flow rate. This calibration factor depends on the Reynolds number and it can be sensitive to the velocity profile behind the nozzle outlet and to presence of upstream flow disturbances such as bends, valves, etc. when the meter is installed on-site. In this paper, CFD modelling, using OpenFoam software, was employed to analyse the sensitivity of the calibration factor to flow disturbances for two types of disturbing elements; a U-bend and half-plate orifice. The CFD model was validated by comparison with experimental data for the calibration factor and velocity profiles obtained from preliminary LDV measurements with air. Two measurement setups were considered where the velocity is measured either in one point at the nozzle axis or integrated along a line across the nozzle diameter. The results show that the considered disturbing elements cause deviations in the calibration factor in the order of tenths of percent and that the maximal sensitivity of the line-setup to these disturbances is approximately half of the maximal sensitivity of the point-setup. On the other hand, it was shown that the line-setup is more sensitive to the LDV positioning than the point-setup.     

Ultrasonic pulse-Doppler flow meter application for hydraulic power plants

At hydraulic power stations, Pitot tubes have commonly been used to measure flow rates in steel penstocks for performance testing of hydraulic turbines. Due to the difficulties of Pitot tube installation, transit-time ultrasonic flow meters are becoming a popular replacement, but their accuracy is sensitive to velocity profiles that depend on Reynolds numbers and pipe surface roughness. Ultrasonic pulse Doppler flow meters have recently gained favor as suitable tools to measure flow rates in steel penstocks because they can measure instantaneous velocity profiles directly. Field tests were conducted at an actual hydraulic power plant using an ultrasonic pulse Doppler flow meter, and it was found capable of measuring velocity profiles in a large steel penstock with a diameter of over one meter and Reynolds number of more than five million. Furthermore, two ultrasonic transducers were placed on the pipe surface to validate the multi-line measurement of asymmetric flow. Each transducer recorded the velocity profile simultaneously from the pipe centerline to its far wall during plant operation. Velocity profiles were obtained from three-minute measurements to improve the accuracy of flow rate measurements.     

Point-velocity methods for flow-rate measurements in asymmetric pipe flow

Laser Doppler velocimetry (LDV) is characterized by its ability to determine local fluid velocities with high accuracy. Therefore, LDV may also be used for precise flow-rate measurements of turbulent flow in circular ducts. The uncertainty of the measurement depends mainly on the asymmetry of the axial velocity distribution and on the point-velocity method chosen to estimate the flow-rate. LDV-measurements in conjunction with velocity-area methods have been performed under different asymmetric flow conditions yielding errors in the range of one per cent. The experimental data have been transformed into analytical flow profiles, in order to investigate combinations of single-point measurements. As a result, a new multi-point method with variable centre-point factor is introduced, that reduces both the effort and uncertainty in the measurement.     

Systematic investigation of pipe flows and installation effects using laser Doppler anemometry—Part II. The effect of disturbed flow profiles on turbine gas meters—a describing empirical model

For systematic investigations of installation effects and for finding efficient ways to minimise these effects, a research project was initiated at the PTB. It covers the design of an automated test facility using a laser Doppler anemometer, the measurement of velocity profiles downstream of several pipe configurations and flow conditioners, as well as the measurement of the change in the gas meter behaviour, namely the shift of the error curve due to the disturbed velocity profiles.

Part I of this paper (presented in this issue) describes the test facility for the investigation of installation effects and shows the relation between pipe configuration and disturbed flow profile for a wide variety of pipe configurations and flow conditioners.

The second part compares the error shift of turbine meters with the characteristic of disturbed flow profiles. For this, three flow field parameters are used to quantify the disturbances of the velocity profiles such as the swirl intensity, flatness and asymmetry of the profile. Considering this, an empirical model is presented to explain the error shift of a turbine meter as a function of these three flow field parameters. The model will be verified for three types of turbine meters and the results will be discussed.     

Effects of water in oil and oil in water on single-phase flowmeters

The effect of two-phase flow on the performance of a range of single-phase flowmeters has been investigated experimentally using the National Standard Multiphase Flow facilities at NEL. The flowmeters tested were 2-inch and 4-inch positive displacement meters, venturi meters, helicoidal and flat-bladed turbine meters, 2-inch U-tube, 3-inch and 1.5-inch straight tube Coriolis meters and a 4-inch vortex shedding meter. The flowmeters were tested in oil flow with water and water flow with oil. The second component fractions were varied from 3% up to 15% by volume. The aim of the project was to quantify the effect of second-phase fluid components on the basic uncertainty of a range of single-phase. These tests have provided evidence of the suitability of particular flowmeters for two-component flow applications. Comparisons have been made between generic type and size of flowmeter. The oil-in-water and water-in-oil tests indicated that the uncertainty in the outputs of the flowmeters tested were generally within ±1% relative to the reference flowrates, although some errors as high as 5–10% were also observed. Most of the measurements from the turbine flowmeters and the positive displacement flowmeters were within ±0.4% of the reference flowrates.     

Experimental and computational studies on flow behavior around counter rotating blades in a double-spindle deck

Experimental and computational studies were performed to determine the effects of different blade designs on a flow pattern inside a double-spindle counter rotating mower deck. In the experimental study, two different blade models were tested by measuring air velocities using a forward-scatter LDV system. The velocity measurements were taken at several different azimuth and axial sections inside the deck. The measured velocity distributions clarified the air flow pattern caused by the rotating blades and demonstrated the effects of deck and blade designs. A high-speed video camera and a sound level meter were used for flow visualization and noise level measurement. In the computational works, two-dimensional blade shapes at several arbitrary radial sections have been selected for flow computations around the blade model. For three-dimensional computation applied a non-inertia coordinate system, a flow field around the entire three-dimensional blade shape is used to evaluate flow patterns in order to take radial flow interactions into account. The computational results were compared with the experimental results.     

Calibration of hydrogen Coriolis flow meters using nitrogen and air and investigation of the influence of temperature on measurement accuracy

The performance of four Coriolis flow meters designed for use in hydrogen refuelling stations was evaluated with air and nitrogen by three members of the MetroHyVe JRP consortium; NEL, METAS and CESAME EXADEBIT.A wide range of conditions were tested overall, with gas flow rates ranging from (0.05–2) kg/min and pressures ranging from (20–86) bar. The majority of tests were conducted at nominal pressures of either 20 bar or 40 bar, in order to match the density of hydrogen at 350 bar and 20 °C or 700 bar and −40 °C. For the conditions tested, pressure did not have a noticeable influence on meter performance.When the flow meters were operated at ambient temperatures and within the manufacturer's recommended flow rate ranges, errors were generally within ±1%. Errors within ±0.5% were achievable for the medium to high flow rates.The influence of temperature on meter performance was also studied, with testing under both stable and transient conditions and temperatures as low as −40 °C.When the tested flow meters were allowed sufficient time to reach thermal equilibrium with the incoming gas, temperature effects were limited. The magnitude and spread of errors increased, but errors within ±2% were achievable at moderate to high flow rates. Conversely, errors as high as 15% were observed in tests where logging began before temperatures stabilised and there was a large difference in temperature between the flow meter and the incoming gas.One of the flow meters tested with nitrogen was later installed in a hydrogen refuelling station and tested against the METAS Hydrogen Field Test Standard (HFTS). Under these conditions, errors ranged from 0.47% to 0.91%. Testing with nitrogen at the same flow rates yielded errors of −0.61% to −0.82%.     

The consistency of pressure effects between three identical Coriolis flow meters

Coriolis flow meters are one of the most popular flow measurement technologies in the world today for high accuracy measurement of single-phase liquids, gases and even slurries. They are capable of measuring both mass and density directly and can also infer the volume flow. They can be installed in challenging process environments and have been successfully deployed with non-Newtonian fluids, high viscosity fluids, pulsating flows and even at extreme temperatures and pressures.However, it is known that operating most Coriolis flow meters at a pressure which differs from the original calibration pressure requires compensation else significant measurement errors will occur. Pressure compensation coefficients appear to vary by manufacturer, meter geometry and sensor material. Furthermore, the manufacturer published pressure compensation coefficients are not fully traceable. To date, there has not been sufficient research exploring the consistency of the pressure compensation for identical Coriolis flow meters.This paper presents the findings of a research conducted at the TÜV SÜD National Engineering Laboratory (NEL) Elevated Pressure and Temperature (EPAT) oil flow facility to investigate the pressure effect uniformity for matching Coriolis devices. The first stage of the experimental programme calibrated three identical DN80 Coriolis flow meters at a range of pressures with no pressure compensation applied. A pressure compensation coefficient was then derived from the data and the Coriolis meters were then calibrated at two alternative pressures to ascertain the robustness of the coefficients and whether the compensation could be extrapolated successfully.From the experimental results, it can be concluded that the pressure effect for the three DN80 Coriolis flow meters was extremely repeatable and consistent with a discrepancy of less than 0.025% between the devices at 80 bar. Whilst the mass flow was significantly affected by fluid pressure, the fluid density did not appear to be influenced. The pressure corrected results were also well within the manufacturer specification of ±0.1%.     

锥形流量计下游支撑及取压位置的试验研究

锥形流量计应用广泛,其国际标准正在起草中。锥形流量计发展过程遇到两个问题：安全性和制造一致性差,具有双支撑结构的锥形流量计可解决此问题。为保证增加的双支撑结构不会影响锥形流量计的测量性能和较短的表体长度,需要研究下游支撑和下游取压位置。根据锥形流量计尾流流场的速度分布和压力分布的状况设计相关的改进试验,选择合适的下游支撑和下游取压位置。试验使用的锥形流量计经过特殊设计：锥体、下游支撑位置、下游取压位置都可以按照要求变换位置。试验得到适用于不同直径管道的下游取压位置和支撑位置的选取规律。不同管径和等效直径比下的锥形流量计试验数据显示：改进后的双支撑形式的锥形流量计样机比悬臂梁锥形流量计具有更好的流出系数不确定度。     

Influence of flow disturbances on the performance of industry-standard LNG flow meters

In the last decade significant progress has been achieved in the development of measurement traceability for LNG inline metering technologies such as Coriolis and ultrasonic flow meters. In 2019, the world's first LNG research and calibration facility has been realised thus enabling calibration and performance testing of small and mid-scale LNG flow meters under realistic cryogenic conditions at a maximum flow rate of 200 m³/h and provisional mass flow measurement uncertainty of 0.30% (k = 2) using liquid nitrogen as the calibration fluid. This facility enabled, for the first time, an extensive test programme of LNG flow meters under cryogenic conditions to be carried out to achieve three main objectives; the first is to reduce the onsite flow measurement uncertainty for small and mid-scale LNG applications to meet a target measurement uncertainty of 0.50% (k = 2), the second is to systematically assess the impact of upstream flow disturbances and meter insulation on meter performance and the third is to assess transferability of meter calibrations with water at ambient conditions to cryogenic conditions. SI-traceable flow calibration results from testing six LNG flow meters (four Coriolis and two ultrasonic, see acknowledgment section) with water in a water calibration facility and liquid nitrogen (LIN) in the LNG research and calibration facility under various test conditions are fully described in this paper. Water and LIN calibration data were compared and it was observed that the influence of removing the meter insulation on mass flow rate measurement accuracy can be more significant (meter error > ±0.50%) than the influence of many typical upstream disturbances when the meter is preceded by a straight piping length equal to twenty pipe diameters (20D) with no additional flow conditioning devices, in particular for ultrasonic meters. The results indicate that the correction models used to transfer the water calibration to cryogenic conditions (using LIN) can potentially result in mass flow rate measurement errors below ±0.5%, however, the correction models are specific to the meter type and manufacturer. This work shows that the target measurement uncertainty of 0.50% can be achieved if the expanded standard error of the mean value measured by the meter is smaller than 0.40% (k = 2). It is planned to repeat these tests with LNG in order to compare the results with the LIN tests presented in this paper. This may reveal that testing with an explosion safe and environmentally friendly fluid such as LIN produces representative results for testing LNG flow meters.     

Flow rate measurement in flows with asymmetric velocity profiles by means of distributed thermal anemometry

Flow rate in closed conduits is one of the most frequently measured parameters in industrial processes and in gas and water supply. For an accurate measurement, flow meters typically require a fully developed symmetric flow profile with preferably no radial or tangential velocity components. This is commonly secured by mounting flow meters in a pipe at a sufficiently long distance downstream any change in cross-section or pipe direction. In this paper, we introduce a new approach for flow rate measurement of gases or liquids that employs a novel spatially resolving fluid velocity sensor basing on thermal anemometry. The new principle allows accurate flow rate measurements for non-axisymmetric velocity profiles, even directly after pipe bends, T-junctions or other alterations in the pipe geometry. This is exemplified for air flow in three different pipe bend configurations.     

Note: Ultrasonic liquid flow meter for small pipes

An ultrasonic flow meter for small pipes is presented. For metal pipe diameter smaller than 10 mm, clamp-on ultrasonic contrapropagation flow meters may encounter difficulties if cross talk or the short acoustic path contributes to large uncertainty in transit time measurement. Axial inline flow meters can avoid these problems, but they may introduce other problems if the transducer port is not properly positioned. Three types of pipe connecting tees are compared using the computational fluid dynamics (CFD) method. CFD shows the 45° tee has more uniform velocity distribution over the measuring section. A prototype flow meter using the 45° tee was designed and tested. The zero flow experiment shows the flow meter has a maximum of 0.002 m∕s shift over 24 h. The flow meter is calibrated by only 1 meter factor. After calibration, inaccuracy lower than 0.1% of reading was achieved in the laboratory, for a measuring range from 15 to 150 g∕s (0.29 to 2.99 m∕s; Re = 2688 to 26,876).     

Micro-flow metering and viscosity measurement of low viscosity Newtonian fluids using a fibreoptical spatial filter technique

The paper describes an experimental method that is capable of measuring liquid flows of the order of millilitres per hour. Volume flow of laminar flows of Newtonian liquids in pipes or channels can be determined by measurement of the centreline velocity and application of the equation of Hagen-Poiseuille. Micro-flow meters with double fibre-array sensor were developed for the measurements of liquid volume flow in capillaries and micro-channels. The main units of the micro-flow meters are a laser-diode system, a double fibre-array sensor and different transparent capillaries or micro-channels. The accuracy of the measured water volume flow was tested with a balance and a syringe pump with given volume flow. Furthermore, the influence of the size of tracer particles on the volume flow results was also determined. This method of flow metering of Newtonian liquids needs no calibration and the results are not influenced by changes in temperature, pressure or nature of Newtonian liquid. An additional measuring result is the determination of the viscosity function by the application of a stripe model of the two-dimensional micro-channel flow. Possible applications of the fibreoptical micro-flow meter lie in micro- volume flow measurements of different Newtonian liquids and in viscosity measurements of Newtonian and non-Newtonian liquids.     

Performance of the LDA Volumetric Flow Rate Standard Under Severely Disturbed Flow Conditions

Flow meters in thermal power plants are operated at high temperatures and pressures and often encounter disturbed flow profiles. This leads to an increased measurement uncertainty, limiting the safe operating range of flow rates and thus, the plant's power output. To respond to this shortcoming, the laser optical flow rate standard (LFS) was developed. The LFS is designed to allow the on-site calibration of industrial flow meters in power plants at high temperatures and pressures. It makes use of the laser Doppler anemometry (LDA), as a fundamental and non-invasive method, to measure the velocity field simultaneously with two LDA systems. The volumetric flow rate is then determined by means of integration. Here, we present flow rate measurements for a fully developed pipe flow and for six pipe diameters downstream of a disturbance generator. The mean deviation in flow rate between the two LDA systems was 0.05%, with a mean deviation from the gravimetric reference flow rate of 0.12%. The highest deviations from the reference were 0.21% and 0.31%, for the first and second system respectively.     

Accurate mass flow and density of bubbly liquids using speed of sound augmented Coriolis technology

Speed of sound augmented Coriolis technology utilizes a process fluid sound speed measurement to improve the accuracy of Coriolis meters operating on bubbly liquids. This paper presents a theoretical development and experimental validation of speed of sound augmented Coriolis meters. The approach utilizes a process fluid sound speed measurement, based on a beam-forming interpretation of a pair of acoustic pressure transducers installed on either side of a Coriolis meter, to quantify, and mitigate, errors in the mass flow, density, and volumetric flow reported by two modern, dual bent-tube Coriolis meters operating on bubbly mixtures of air and water with gas void fractions ranging from 0% to 5%. By improving accuracy of Coriolis meters operating on bubbly liquids, speed of sound augmented Coriolis meters offer the potential to improve the utility of Coriolis meters on many existing applications and expand the application space of Coriolis meters to address additional multiphase measurement challenges.The sources of measurement errors in Coriolis meters operating on bubbly liquids have been well-characterized in the literature. In general, conventional Coriolis meters interpret the mass flow and density of the process fluid using calibrations developed for single-phase process fluids which are essentially incompressible and homogeneous. While these calibrations typically provide sufficient accuracy for single-phase flow applications, their use on bubbly liquids often results in significant errors in both the reported mass flow, density and volumetric flow. Utilizing a process fluid sound speed measurement and an empirically-informed aeroelastic model of bubbly flows in Coriolis meters, the methodology developed herein compensates the output of conventional Coriolis meters for the effects of entrained gas to provide accurate mass flow, density, volumetric flow, and gas void fraction of bubbly liquids.Data presented are limited to air and water mixtures. However, by influencing the effective bubble size through mixture flow velocity, the bubbly liquids tested exhibit decoupling characteristics which spanned theoretical limits from nearly fully-coupled to nearly fully-decoupled flows. Thus, from a non-dimensional parameter perspective, the data presented is representative of a broad range of bubbly liquids likely to be encountered in practice.     

Estimation of uncertainty of mean velocity of flue gas in a conduit as determined by the traverse method within the gravimetric measurement of particulate concentration

In gravimetric measurements of dust emissions from industrial technological plants, the required mean gas velocity in a conduit is often determined by Pitot traverse method. It is commonly seen as a method giving good approximate values of mean gas velocity, although the actual rate of this approximation is not considered in the analysis of measurement results. It was seen that there was a need to establish what magnitude of error might occur in practice due to the small number of measurement points and typical non-uniformity of the gas velocity profiles in conduits of rectangular cross-section. The calculations were based on the concept of treating a measurement plane as one consisting of a set of elementary planes. The elementary gas velocity profiles in these elementary planes were simulated, the mean velocity for these profiles were calculated based on point velocity values, and the measurement uncertainty of this mean velocity determined. This uncertainty results in the uncertainty of the mean velocity across the entire measurement plane. It appears that, depending on the number of measurement points and gas velocity profile non-uniformity, the value is not small and is of the order of several percent, and hence needs to be taken into account in the budget of the combined uncertainty of mean velocity, which in turn contributes to the uncertainty of gas volumetric flow rate and dust pollutant mass flow rate.     

Water flow measurement in large bore pipes: an experimental comparison between two different types of insertion flowmeters

In this paper the metrological behavior of two different insertion flowmeters (magnetic and turbine types) in large water pipes is described. A master-slave calibration was carried out in order to estimate the overall uncertainty of the tested meters. The experimental results show that (i) the magnetic insertion tested flowmeter performs the claimed accuracy (+/- 2%) within all the flow range (20:1); (ii) the insertion turbine tested meter, instead, reaches the claimed accuracy just in the upper zone of the flow range.     

Uncertainty analysis of the high pressure closed loop gas flow standard facility in NIM

High pressure air flow standard facilities, including the pVTt facility, sonic nozzle facility and closed loop facility were built in NIM at the end of 2014. The high pressure closed loop gas flow facility was the first closed loop facility in China. The system has 4 sets of 100 mm diameter turbine meters for the reference meters with a flow range of (40–1300) m³/h and a pressure range of (190–2500) kPa. To avoid uncertainties introduced during installation, the reference meters were designed to be calibrated in situ using the sonic nozzle facility. The uncertainty in the pressure measurement was reduced by installing an absolute pressure transducer in the manifold upstream of the reference meters, with differential pressure transducers used to measure the pressure drops across the reference flow meter and the test flow meter. The relative expanded uncertainty for the test meter can reach 0.20% (k = 2) as verified by comparison the sonic nozzle facility and the closed loop facility measurements.     

Vertically installed Venturi tubes for wet-gas flow measurement: Possible improvements to ISO/TR 11583 to extend its range of applicability

Venturi tubes are commonly used for wet-gas flow measurement, and the majority of commercial wet-gas flow meters generally include a Venturi tube installed vertically with embedded secondary instrumentation. The presence of the liquid causes an increase in the measured differential pressure and results in the Venturi tube over-reading the actual amount of gas passing through the meter. Most of the research in the literature is focused on the investigation of the over-reading for horizontally oriented Venturi tubes, thus limiting the development of over-reading correlations for vertical installation. An experimental campaign was recently conducted at the TÜV SÜD National Engineering Laboratory (NEL) high-pressure wet-gas loop, where three Venturi tubes of the same nominal diameter (4”) but different throat to inlet diameter ratio (0.4, 0.6, 0.75) were tested, installed vertically after a blind tee. The results of this experimental campaign are presented in this paper and the effects of various parameters (line pressure, gas Froude number, diameter ratio) on the over-reading are briefly discussed. It is shown that the over-reading correlation included in the ISO/TR 11583:2012 and developed for horizontally oriented Venturis, is not applicable to vertically oriented Venturis. However, if modified, the correlation included in the ISO/TR 11583 is capable of meeting its stated uncertainty limits for the experimental data presented here for vertically installed Venturis.