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.     

A new mass & time primary standard for natural gas in China and the uncertainty evaluation

A new mass-time primary standard for high pressure natural gas, which is based on electromagnetic balance and hydraulic fast-acting valves, was set up at the beginning of 2017 in Chengdu, China. The full load of the electromagnetic balance is 3 tons and the measurement uncertainty of mass is better than 1.0g(k = 2). The opening and closing time of the hydraulic fast-acting valves can achieve 33 ms±3 ms.The operation pressure and flowrate range of the facility is (4–60)bar.a and (5–410)m³/h respectively. In accordance with the preliminary tests, the estimate uncertainty of sonic nozzles calibration is between 0.10% and 0.12%(k = 2). The operation principle, testing results and the uncertainty evaluation are presented in the paper as well as some improving ideas.     

A new calibration facility for water flowrate at high Reynolds number

A new test facility has been constructed for the National Metrology Institute of Japan (NMIJ) and the National Institute of Advanced Industrial Science and Technology (AIST) for calibration of feedwater flowmeters used in nuclear power stations at Reynolds numbers of up to 18 million. This very large Reynolds number is achieved in a 600 mm pipe at a flowrate of 3.33  m³/s (12,000  m³/h) and a water temperature of 70  ^°C. This calibration facility consists of a circulation loop with four pumps and four reference flowmeter sets, a prover system, a heating and cooling unit, and other components. The expanded uncertainty of this facility is 0.077%. The present paper describes, in detail, the new facility, the calibration method of the reference flowmeter, experiments for flow field, uncertainty estimation, and the results of an example calibration.     

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.     

An orifice meter for bidirectional air flow measurements: Influence of gas thermo-hygrometric content on static response and bidirectionality

This paper presents the design and calibration of an ISO non-compliant orifice plate flowmeter whose intended use is for respiratory function measurements in the bidirectional air flow range ±9 L/min.The novelty of the proposed sensor consists of a plate beveled in both upstream and downstream sides: a symmetrical geometry is adopted in order to perform bidirectional measurements of flow rate. A mathematical model is introduced to quantify the influence of temperature on the sensor output. Four different positions of the pressure static taps are evaluated in order to maximize bidirectionality. An index is also introduced in order to quantitatively estimate the anti-symmetry of the sensor's response curve.Trials are carried out to evaluate the influence on sensor output of air temperatures (22 °C, 30 °C and 37 °C) at different values of relative humidity (5%, 55% and 85%). Experimental data show a quite good agreement with the theoretical model (R²>0.98 in each condition).The influence of air temperature on the sensor output is minimized by introducing a correction factor based on the theoretical model leading to measurement repeatability better than 2% in overall range of calibration. The mean sensitivity in the calibration range is about 2 kPa L⁻¹·min allowing to obtain a sensor discrimination threshold lower than 0.2 L/min in both directions. The time constant of the whole measurement system, equal to 2.40±0.03 ms, leads to a bandwidth up to 80 Hz making the sensor suitable for respiratory function measurements.     

Study on the parallel pressure differential type gas laminar flow sensing technique

Parallel pressure differential (PPD) type laminar flow sensing technique was invented several years ago to reduce nonlinear effect in a traditional laminar flow element (LFE). In this paper, the internal flow of each branch in a PPD LFE is numerically simulated for gas flow. The results show that the relative deviation of the pressure drops of the two branches in a PPD LFE is within ±0.05% as inlet mass flow being the same, indicating that the flow resistance characteristics of the two branches are consistent, which means that the hypothesis of a same flow rate for the two branches in a real PPD LFE is tenable. There is little difference, ±0.01%, in the local pressure losses of the two upstream capillaries outlet flows, which can be ignored in a real measurement, further verifying that the theoretical analysis of the PPD principle is reliable. Capillary length effect in a PPD LFE is also examined. The bigger capillary length, the higher measurement precision can be achieved for a certain length range. For instance, it is suggested that the length of the short components should not be shorter than the laminar flow dimensionless entrance length defined by X_e (L_e/d/Re, where L_e is the entrance length) = 0.035, for flow measurement uncertainty within ±1.0%. The simulation and experiment results of gas flow show that the suitable value of K_exp is 1, and in the flow range of (0.0256–5.2985) m³/h measurement error of a PPD LFE is within ±0.8% only with expansion correction, indicating that the PPD laminar flow measurement technique is suitable for the gas flow.     

Assessment of combined V/Z clamp-on ultrasonic flow metering

Clamp-on ultrasonic flow metering can provide a non-invasive and portable means for flow measurement. However, it indicates flow rates with low measurement accuracy at low flow velocity in pipe flows. Typical accuracy of the clamp-on ultrasonic flow metering amounts as low as ±1% if the flow velocity in a pipe is greater than 0.5 m/s. The accuracy can be increased greater than ±2% if the flow velocity is lowered smaller than 0.5 m/s. Inner pipe diameter can be also an influential factor in flow metering when the exact value of the inner diameter is not known. The inner pipe diameter cannot be found if the pipe is too large to measure or if there are erosions or adhesions on the inner pipe surface due to small particles in the flow. These shortcomings of the clamp-on ultrasonic flow metering can be overcome by combining two transit times along a Z-shaped and a V-shaped ultrasonic path. This technique is termed combined V/Z clamp-on ultrasonic flow metering. With the water flow standard system in KRISS, this combined technique exhibited intermediate performance between the two flow metering techniques along the Z-shaped and the V-shaped ultrasonic paths. Notably, the combined technique showed better performance (expanded uncertainty less than 0.76%, k = 2) than the two flow metering techniques (1.61% and 1.17%, k = 2) in the flow range of (100–400) m³/h with pipe diameter of 250 mm.     

On-site calibration system for trace humidity sensors

A portable device for calibration of trace humidity sensors and an adopted calibration procedure have been developed. The calibration device is based on humidity generation by permeating water through polymeric membrane tubes. Water vapour transmission rates for various polymers were experimentally determined in order to select the most suitable polymeric material. The developed trace humidity generator consists of a gas-flow polymeric hose immersed in a water reservoir thermostated by a sensor-controlled heater. Mole fractions of water vapour between 1 μmol mol⁻¹ and 350 μmol mol⁻¹ (equivalent to frost-point temperatures from −76 °C to −31 °C) were generated by varying either the operating temperature or gas flow. The operating temperature can be varied from 20 °C to 60 °C and kept stable within 0.1 K. Uncertainty analysis indicated that the trace humidity generator produces gas flows of constant humidity amounts with a relative expanded uncertainty less than 3.4% (k = 2) of the generated value.     

Development and validation of a dynamic primary standard for unsteady liquid flow calibration

LNE-CETIAT liquid flow laboratory is the French Designated Institute for liquid water flow rate from 1 g h⁻¹ to 50 t h⁻¹. Historically, its primary standards are based on the flying start and stop gravimetric method. The best relative expanded uncertainty for liquid mass flow rate is 0.05% (k = 2). In the scope of the Joint Research Project Metrowamet and its mission to maintain and develop the French standards for liquid flow, LNE-CETIAT has developed and validated a dynamic primary standard for unsteady liquid flow calibration. This paper will first present the developped system, which is composed of a dynamic flow generator and a dedicated measuring system together with its own software for data acquisition and processing. The validation, realized by intra and inter-laboratory comparisons for static and dynamic flows, is presented in the third chapter. Finally, the validation of the measurement and calibration capabilities, based on internal tests and inter-laboratory comparisons are presented.     

Gas Oil Piston Prover,primary reference values for Gas-Volume

The paper describes the design, measurement results and uncertainty analyses of the hydraulic driven piston-prover system which has been in operation at VSL since 2008. The 12-meter long, 0.6 m bore piston-prover is used for the realization of Reference Values for Gas-Volume at pressures between 1 and 65 bar(a) at several gases. The principle is based on the displacement of a piston acting as a Gas–Oil separator. The standard has a flow-rate range from 5 to 230 m³/h. The system is designed to calibrate reference meters. The Calibration and Measurement Capability (CMC) of the system is proven to be smaller than 0.1% (k=2). The paper also explains the coherence between the Gas–Oil piston-prover and other traceability generators and ‘flow rate bootstrapper systems’.     

Liquid low-flow calibration rig using syringe pump and weighing tank system

A calibration rig consisting of a syringe pump and a weighing tank system that can operate in the flow rate range of 0.02–60 L/h was developed in this study. This paper discusses the design considerations of the calibration methods, the development of the rig, the calibration results, and the uncertainty analysis conducted on the rig. A weighing tank system that minimizes the effects of outlet tube contact and evaporation was developed. The syringe pump system was designed using a servomotor, a precise ball screw, and a linear encoder, and it was calibrated using the developed weighing tank system via the standing start and stop method over the target range of flow rates with light oil and industrial gasoline. Several flowmeters were calibrated using the syringe pump via the flying start and finish method. During the flowmeter calibration stage, the effect of the evaporation error was eliminated because the calibration rig can form a closed pipeline system. The influence of dissolved gas and the position dependence of the syringe pulse factor on the calibration accuracy were investigated experimentally. As a result, all obtained syringe pulse factors were found to be within ±0.02% of each other. The preliminary expanded uncertainties (k=2) of the calibration rig were estimated to be 0.066% and 0.070% for mass and volumetric flows, respectively.     

Calibration of an ultrasonic flow meter for hot water

If we want to keep the number of necessary characterisation measurements within acceptable limits, we need to be confident that a flow instrument design reacts in a predictable and straightforward way to systematic influences. In this paper, the important systematic influences for an ultrasonic flow meter (UFM) for feed water flow are identified to decide which characterisations have to be carried out in addition to a typical baseline calibration with water at 20 °C. In heat metering applications where there are temperatures up to 120 °C it is for example known that the temperature influence on the flow instrument is important and this also applies to higher temperatures such as in the feed water control of power plants. One of the critical systematic temperature influences that affects most flow instruments is the thermal expansion of the meter body. From June 2009 to March 2010, the “Heat and Vacuum” department of the Physikalisch-Technische Bundesanstalt conducted a measurement campaign to characterise the influence of thermal expansion of a meter body on the calibration of an 8 inch (DN 200) five chord UFM for feed water application in the temperature range from 4 °C to 85 °C and flow range from 50 m³ h⁻¹ to 900 m³ h⁻¹. An overview of the procedures and facility used for the calibration is given and the measurement conditions under which the calibrations were performed are detailed. It is shown that a linear model of the thermal expansion effect is appropriate for the investigated conditions.     

Development of an experimental setup for microflow measurement using interferometry

The precise measurement of micro and nanoflow of incompressible liquids (below 1 μL/h) is a complex task due to several factors involved in, namely, evaporation, adsorption and the existence of air bubbles within the system. Nevertheless, the importance of its measurement is undeniable in equipment such as insulin pumps, or medical drug delivery devices for new-born, microchip flow pumps, to mention few.The work herein presented was developed in a partnership between the Volume and Flow Laboratory (LVC) of the Portuguese Institute of Quality (IPQ) and the Department of Mechanical and Industrial Engineering (DEMI) of The New University of Lisbon under the project MeDD II – Metrology for Drug Delivery. It had the main objective of conceiving a new Portuguese standard for the measurement of ultra-low flow using interferometry, with a target uncertainty of 1% (k = 2). Therefore, the new setup relies on an interferometer made up of a laser unit, two retroreflector cubes, one beam splitter, as well as a flow generator (a Nexus syringe pump) and a computer for data acquisition.Experimental tests on a Flow generator and a Coriolis flow meter were carried out at different flow rates. With the innovative methodology developed during the present research, it was possible to measure flow rates of an incompressible fluid (water) down to 1 μL/h with an uncertainty of 3% (k = 2).     

Direct measurement of skin-friction in shock/boundary-layer interaction flows

The direct measurement of skin friction at high speed is extraordinarily complicated due to the interference from various extraneous forces and the short test-time of high-speed facilities. The present study deals with the design and performance assessment of a skin friction sensor in a hypersonic flowfield with shock-boundary layer interaction, which is a predominant high-speed flow phenomenon. The experiment was conducted in the IIT Bombay Shock Tunnel (IITB-ST); the sensor was exposed to a flow with freestream Mach number, total enthalpy, and Reynolds number of 8.4, 0.69 MJ/kg, and 2.60 × 10⁶ m⁻¹, respectively. The shock-boundary layer interaction was induced by an oblique shock impinged on a flat plate, with a flow turn angle of 15°. The low magnitude average skin friction could be measured with an uncertainty of ±21%. The comprehensive study conducted confirmed the suitability of the skin friction sensor for high-speed applications in impulse facilities.     

Determination of the thermal conductivity of composted material

The objective of this study was to develop a reliable method for the determination of the thermal conductivity of composted material using the TP08 probe. Study was set out to determine whether the selection of a signal fragment used to establish thermal conductivity (λ), has a significant influence on the results. Also minimum number of measurements was determined for every phase of the composting process. No significant differences were reported between results, but certain changes in the value of λ were noted. In successive stages of the process, thermal conductivity of composted material were: 0.31 ± 0.09, 0.45 ± 0.14, 0.27 ± 0.03 and 0.37 ± 0.17 W m⁻¹ K⁻¹.     

Constant pressure primary flow standard for gas flows from 0.01 cm3/min to 100 cm3/min (0.007–74 μmol/s)

We describe a flow standard for gas flows in the range from 0.01 sccm to 100 sccm with a relative standard uncertainty (68% confidence) of 0.03% at 1 sccm (1 sccm≡1 cm³/min of an ideal gas at 101325 Pa and 0 °C ≈ 0.74358 μmol/s). The flow standard calibrates a secondary meter by withdrawing a piston from a cylinder held at constant pressure P while gas flows from the secondary meter into the cylinder. The flow standard can operate anywhere in the range 10 kPa<P<300 kPa, and it can act as a flow source as well as a flow receiver. The flow standard incorporated features that improved its convenience and lowered its cost without sacrificing accuracy, specifically (1) dry sliding seals made with commercially available, easily replaced, o-rings, (2) a compact design based on a commercially available, hollow piston, and (3) a linear encoder with a small Abbe error.     

Classification of vertebral column disorders and lumbar discs disease using attribute weighting algorithm with mean shift clustering

In this article, a new data pre-processing method has been suggested to detect and classify vertebral column disorders and lumbar disc diseases with a high accuracy level. The suggested pre-processing method is called the Mean Shift Clustering-Based Attribute Weighting (MSCBAW) and is based primarily on mean shift clustering algorithm finding the number of the sets automatically. In this study, we have used two different datasets including lumbar disc diseases (with two classes-our database) and vertebral column disorders datasets (with two or three classes) taken from UCI (University of California at Irvine) machine learning database to test the proposed approach. The MSCBAW method is working as follows: first of all, the centres of the sets automatically for each characteristics in dataset by using the mean shift clustering algorithm are computed. And then, the mean values of each property in dataset are calculated. The weighted datasets by multiplying these mean values by each property value in the dataset that have been obtained by dividing the above mentioned mean values by the centres of the sets belonging to the relevant property are achieved. After the data weighting stage, three different classification algorithms that included the k-NN (k-Nearest Neighbour), RBF–NN (Radial Basis Function–Neural Network) and SVM (Support Vector Machine) classifying algorithms have been used to classify the datasets. In the classification of vertebral column disorders dataset with two classes (normal or abnormal), while the obtained classification accuracies and kappa values were 78.70% ± 0.455 (the classification accuracy ± standard deviation), 81.93% ± 0.899, and 80.32% ± 0.56 using SVM, k-NN (for k = 1), and RBF–NN classifiers, respectively, the combinations of MSCBAW and SVM, k-NN (for k = 1), and RBF–NN classifiers were obtained 99.03% ± 0.977, 99.67% ± 0.992, and 99.35% ± 0.9852, respectively. In the classification of second dataset named vertebral column disorders dataset with three classes (Normal, Disk Hernia, and Spondylolisthesis), while the obtained classification accuracies and kappa values were 74.51% ± 0.581, 78.70% ± 0.659, and 83.22% ± 0.728 using SVM, k-NN (for k = 1), and RBF–NN classifiers, respectively, the combinations of MSCBAW and SVM, k-NN (for k = 1), and RBF–NN classifiers were obtained 99.35% ± 0.989, 96.77% ± 0.948, and 99.67% ± 0.994, respectively. As for the lumbar disc dataset, while the obtained classification accuracies and kappa values were 94.54% ± 0.974, 94.54% ± 0.877, and 93.45% ± 0.856 using SVM, k-NN (for k = 1), and RBF–NN classifiers, respectively, the combinations of MSCBAW and SVM, k-NN (for k = 1), and RBF–NN classifiers were obtained 100% ± 1.00, 99.63% ± 0.991, and 99.63% ± 0.991, respectively. The best hybrid models in the classification of vertebral column disorders dataset with two classes, vertebral column disorders dataset with three classes, and lumbar disc dataset were the combination of MSCBAW and k-NN classifier, the combination of MSCBAW and RBF–NN classifier, and the combination of MSCBAW and SVM classifier, respectively.     

Uncertainty evaluation of a 10N·m dead weight torque standard machine and comparison with a 1kN·m dead weight torque standard machine

A 10N·m dead weight torque standard machine (10-N·m-DWTSM) has been developed and evaluated since 2006 at the National Metrology Institute of Japan (NMIJ), a part of the National Institute of Advanced Industrial Science and Technology (AIST). Previously, the lengths of a moment arm, made of a low-thermal-expansion alloy (Super Invar), and the sensitivity limit of the fulcrum were evaluated. However, it is known that mechanical parts made of Super Invar vary in size with time. Therefore, the sensitivity limit of the fulcrum should be investigated under real calibration conditions. In this study, the moment arm lengths and the sensitivity limit of the fulcrum were re-evaluated. The moment arm lengths were found to have increased by an average of 6.3 μm in five years. The relative combined standard uncertainty of the moment arm length, w_arm, was re-evaluated in consideration of the uncertainty of the secular length change and was found to be 1.8 × 10⁻⁵. The sensitivity limit of the fulcrum was investigated by using a highly accurate, small-rated-capacity torque measuring device. The relative combined standard uncertainty due to the sensitivity limit of the fulcrum was 2.5 × 10⁻⁵ in the 0.1–10N·m torque range. The uncertainty budget table of the 10-N·m-DWTSM was completed. The relative expanded uncertainty of torque realized by the 10-N·m-DWTSM, W_tsm, was evaluated in the 0.1–10N·m torque range and was found to be 6.6 × 10⁻⁵, with a coverage factor, k, being equal to 2. In addition, the 10-N·m-DWTSM was compared with the existing 1-kN·m-DWTSM at NMIJ by using small-rated-capacity torque measuring devices at 5N·m and 10N·m torque steps. Two loading conditions were adopted in this comparison. The comparison results showed good agreement within the uncertainties in all cases. Thus, the torque realized by the 10-N·m-DWTSM was shown to be equivalent to that achieved by the 1-kN·m-DWTSM.     

An ultra high-pressure test rig for measurements of small flow rates with different viscosities

Within the framework of a research project regarding investigations on a high-pressure Coriolis mass flow meter (CMF) a portable flow test rig for traceable calibration measurements of the flow rate (mass - and volume flow) in a range of 5 g min⁻¹ to 500 g min⁻¹ and in a pressure range of 0.1 MPa to 85 MPa was developed. The measurement principle of the flow test rig is based on the gravimetrical measuring procedure with flying-start-and-stop operating mode. Particular attention has been paid to the challenges of temperature stability during the measurements since the temperature has a direct influence on the viscosity and flow rate of the test medium. For that reason the pipes on the high-pressure side are double-walled and insulated and the device under test (DUT) has an enclosure with a separate temperature control. From the analysis of the first measurement with tap water at a temperature of 20 °C and a pressure of 82.7 MPa an extensive uncertainty analysis has been carried out. It was found that the diverter (mainly due to its asymmetric behaviour) is the largest influence factor on the total uncertainty budget. After a number of improvements, especially concerning the diverter, the flow test rig has currently an expanded measurement uncertainty of around 1.0% in the lower flow rate range (25 g min⁻¹) and 0.25% in the higher flow rate range (400 g min⁻¹) for the measurement of mass flow. Additional calibration measurements with the new, redesigned flow test rig and highly viscous base oils also indicated a good agreement with the theoretical behaviour of the flow meter according to the manufacturers׳ specifications with water as test medium. Further improvements are envisaged in the future in order to focus also on other areas of interest.     

Velocity distribution of liquid phase at gas-liquid two-phase stratified flow based on particle image velocimetry

Horizontal gas-liquid flows are commonly encountered in the production section of the oil and gas industry. To further understand all parameters of the pipe cross-section, this paper use particle image velocimetry to study the circular pipe cross-section liquid velocity distribution rule. Firstly the focus is on the software and hardware combination of image correction system, to solve the influence of different refractive indexes of medium and pipeline curvature caused by image distortion. Secondly, the velocity distribution law of the corrected stratified flow (the range of liquid flow of 0.09-0.18 m³/h, and gas flow range of 0.3-0.7 m³/h) cross-section at different flow points of the pipeline cross-section at x=0 and in the Y direction at the maximum liquid velocity is studied. It is found that these distribution laws are caused by the influence of the interphase force of the gas-liquid interface and the resistance of the pipe wall. The current measurements also produce a valuable data set that can be used to further improve the stratified flow model for gas-liquid flow.