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National Measurement System

Explore our Publications section to access the work carried out by our flow measurement experts as part of the NMS research programmes.

Published papers

Read some of our recent academic journal articles to learn more about the research carried out at the UK’s Designated Institute for Flow and Density Measurement.

  • Calibrating and Operating Coriolis Flow Meters With Respect to Process Effects

    Dr Chris MillsMarch 2020, Flow Measurement and Instrumentation, Vol. 71.

    The temperature, pressure and viscosity of produced oil from a reservoir can differ considerably from standard calibration laboratory conditions. The standard practice for calibrating flow meters for the oil & gas industry has been to match the fluid viscosity and, if possible, the fluid temperature and pressure. However, matching all parameters is seldom possible due to the limitations set by the calibration facilities. As such, the parameter that is most often matched is the fluid viscosity. A limitation of the above approach is that temperature and pressure variations are known to influence properties, other than fluid viscosity, that may also be critical to the overall measurement uncertainty.

    To address this, NEL have built and commissioned a fully accredited elevated pressure and temperature (EPAT) liquid flow facility. This facility has been used to investigate the performance of flow meters at elevated pressures and temperatures. It also allows for liquid flow calibrations to be completed close to service conditions. This work will provide traceable data on the performance of Coriolis flow meters when operated at elevated pressures and temperatures. This data can then be used to update the Coriolis ISO standard 10790. At present, the latest revision in 2015 includes little practical guidance for the operation of Coriolis meters at elevated pressures, temperatures and viscosities.

    Unfortunately, the methodology for calibrating and operating Coriolis meters at elevated conditions appears fragmented.

    The purpose of this paper will be to highlight the influence of elevated temperatures, pressures and viscosities and to provide the end user with the correct methodology for calibrating Coriolis meters for these conditions. The paper will also highlight the requirement for the ISO standard 10790 to be updated given the current knowledge level.

    Author: Chris Mills
    Journal: Flow Measurement and Instrumentation
    Volume 71, March 2020, 101649

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

    Marc MacDonald, February 2021, Flow Measurement and Instrumentation, 101915

    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%.

    Author: Marc MacDonald, Marc de Huu, Rémy Maury, Oliver Büker
    Journal: Journal of Flow Measurement and Instrumentation

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  • High-speed density measurement for LNG and other cryogenic fluids using electrical capacitance tomography

    Dr Asaad KenbarJanuary 2021, Cryogenics, Vol 113

    The global custody transfer market for liquefied natural gas (LNG) has grown at a strong pace in the last decade and use of LNG as transport fuel has considerable environmental benefits. The quantity of LNG is traded on the basis of energy transferred, calculated from volume, density and gross calorific value. High-speed, accurate density measurement is therefore of significant commercial value.

    The electrical capacitance tomography (ECT) device described in this paper has the potential to measure the LNG density rapidly, on-line at a moderate cost. Continuous monitoring of variation in LNG density during dynamic LNG flow measurement also gives a good indication of change in fluid quality and thus onset of boiling which is known to affect measurement accuracy. ECT is a leading candidate to be explored for online density measurements through measurement of electrical permittivity, as in addition to average value, it offers the image of permittivity across the whole flow conduit, allowing localised bubbles, boiling or other variations to be identified and measured.

    We report here experiments to explore the use of ECT in cryogenic applications. An 8-electrode test ECT sensor was designed, built and tested in laboratory conditions and then in liquid nitrogen. The resolution and imaging capability in cryogenic conditions are shown to be comparable to that under laboratory conditions. The experiments reported here use liquid nitrogen as an analogue fluid, but the results presented are believed to be representative of many cryogenic fluids. Although the use of ECT has been widely reported in the literature for multiphase flows in general, its use has not previously been reported for cryogenic flows. This paper offers proof of principle for ECT cryogenic multi-phase density and flow measurement.

    Dielectric constant is strongly linked to fluid density, and the ECT sensor design tested here shows an estimated measurement of the relative permittivity of liquid nitrogen of 1.45 with a standard measurement error of 0.034. Measurement stability at cryogenic conditions gave an rms variation of output under static conditions of better than 0.001 relative permittivity units even though it was unguarded and only a single electrode ring. The primary errors are associated with the unguarded nature of the test sensor, which was primarily designed as a proof of concept and material demonstrator.

    In addition, such an ECT sensor would provide clear images of any gas in the liquid and give a good estimation of the concentration and velocity of the gas bubbles. The scope of this work is to provide a proof of concept of the cryogenic ECT sensor.

    Authors: Andrew Hunt, Jihar Rusli, Menne Schakel. Asaad Kenbar
    Journal: Cryogenics
    Volume 113, January 2021

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  • Quantative evaluation of the joint effect of uncertain parameters in CO2 storage in the Sleipner project using data-driven models

    Dr Behzad NobakhtDecember 2020, International Journal of Greenhouse Gas Control, Vol 103

    Several researchers have studied the Sleipner model to understand the inherent flow physics better, to find a satisfactory match of the CO2 plume migration. Various sources of uncertainty in the geological model and the fluid have been investigated. Most of the work undertaken on the Sleipner model employed the one factor at a time (OFAT) method and analysed the impact of uncertain parameters on plume match individually.

    In this study, we have investigated the impact of some of the most cited sources of uncertainties including porosity, permeability, caprock elevation, reservoir temperature, reservoir pressure and injection rate on CO2 plume migration and structural tapping in the Sleipner. We tried to fully span the uncertainty space on Sleipner 2019 Benchmark (Layer 9) using a vertical-equilibrium based simulator. To the best of our knowledge, this is the first time that a study has focused on the joint effect of six uncertain parameters using data-driven models. This work would raise our scientific understanding of the complexity of the impact of the reservoir uncertainty on CO2 plume migration in a real field model. The caprock elevation was shown to be the most important parameter in controlling the plume migration (overall importance of 26 %) followed by injection rate (24 %), temperature (22 %), heterogeneity in permeability (13 %), pressure (9 %) and porosity (6 %).

    Authors: Masoud Ahmadinia, Seyed M Shariatipour, Odd Andersen, Behzad Nobakht
    Journal: International Journal of Greenhouse Gas Control
    Volume 103, December 2020

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  • Design of gravimetric primary standards for field-testing of hydrogen refuelling stations

    Marc MacDonald, June 2020, Journal of Flow Measurement and Instrumentation

    The Federal Institute of Metrology METAS developed a Hydrogen Field Test Standard (HFTS) that can be used for field verification and calibration of hydrogen refuelling stations. The testing method is based on the gravimetric principle. The experimental design of the HFTS as well as the description of the method are presented here. The HFTS has been tested at METAS with nitrogen gas at −40 °C to mimic a refuelling process in the field. Laboratory tests have shown that icing on the pipes of the HFTS have a non-negligible impact on the results. Field-testing with the HFTS has also been performed at the Empa hydrogen refuelling station with hydrogen at up to 70 MPa. The major uncertainty components have been identified and assigned values. The required expanded uncertainty of 0.3% could be achieved. A detailed uncertainty budget has been presented and shows that the scale is the largest contributor; buoyancy corrections only play a minor role. For the lowest uncertainty measurements, appropriate waiting times or cleaning methods to get rid of icing are required.

    Author: Marc MacDonald
    Journal: Journal of Flow Measurement and Instrumentation
    01 June 2020

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  • Hydrogen refuelling station calibration with a traceable gravimetric standard

    Marc MacDonald, August 2020, Journal of Flow Measurement and Instrumentation

    Of all the alternatives to hydrocarbon fuels, hydrogen offers the greatest long-term potential to radically reduce the many problems inherent in fuel used for transportation. Hydrogen vehicles have zero tailpipe emissions and are very efficient. If the hydrogen is made from renewable sources, such as nuclear power or fossil sources with carbon emissions captured and sequestered, hydrogen use on a global scale would produce almost zero greenhouse gas emissions and greatly reduce air pollutant emissions.The aim of this work is to realise a traceability chain for hydrogen flow metering in the range typical for fuelling applications in a wide pressure range, with pressures up to 875 bar (for Hydrogen Refuelling Station - HRS with Nominal Working Pressure of 700 bar) and temperature changes from −40 °C (pre-cooling) to 85 °C (maximum allowed vehicle tank temperature) in accordance with the worldwide accepted standard SAE J2601. Several HRS have been tested in Europe (France, Netherlands and Germany) and the results show a good repeatability for all tests. This demonstrates that the testing equipment works well in real conditions. Depending on the installation configuration, some systematic errors have been detected and explained. Errors observed for Configuration 1 stations can be explained by pressure differences at the beginning and end of fueling, in the piping between the Coriolis Flow Meter (CFM) and the dispenser: the longer the distance, the bigger the errors. For Configuration 2, where this distance is very short, the error is negligible.

    Author: Marc MacDonald
    Journal: Journal of Flow Measurement and Instrumentation
    01 August 2020

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  • Gas Hydrates in Sustainable Chemistry

    Dr Edris JoonakiJune 2020, Chemical Society Reviews

    Gas hydrates have received considerable attention due to their important role in flow assurance for the oil and gas industry, their extensive natural occurrence on Earth and extraterrestrial planets, and their significant applications in sustainable technologies including but not limited to gas and energy storage, gas separation, and water desalination. Given not only their inherent structural flexibility depending on the type of guest gas molecules and formation conditions, but also the synthetic effects of a wide range of chemical additives on their properties, these variabilities could be exploited to optimise the role of gas hydrates. This includes increasing their industrial applications, understanding and utilising their role in Nature, identifying potential methods for safely extracting natural gases stored in naturally occurring hydrates within the Earth, and for developing green technologies. This review summarizes the different properties of gas hydrates as well as their formation and dissociation kinetics and then reviews the fast-growing literature reporting their role and applications in the aforementioned fields, mainly concentrating on advances during the last decade. Challenges, limitations, and future perspectives of each field are briefly discussed. The overall objective of this review is to provide readers with an extensive overview of gas hydrates that we hope will stimulate further work on this riveting field.

    Author: Dr Edris Joonaki
    Journal: Chemical Society Reviews 
    Advance Article

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  • Coriolis Meter Density Errors Induced by Ambient Air and Fluid Temperature Differentials

    Dr Gordon Lindsay, June 2020, Flow Measurement and Instrumentation, Vol 73

    Coriolis metering technology is widely applied throughout industry. In addition to the mass flow rate, a Coriolis meter can measure fluid density based on the resonant frequency of the flow tube vibration. There is currently increasing interest in utilising this density measurement capability as the primary process value in applications such as precision control for fluid property conditioning, and fluid contamination monitoring.

    However, within these applications, ambient temperature variation can be significant.

    This paper details research data obtained using TÜV SÜD National Engineering Laboratory's ‘Very Low Flow’ single-phase facility. The rig was modified to include a programmable temperature enclosure in which a Coriolis meter was installed. Two commercial meter models from the same manufacturer were tested. Both meters showed fluid density errors when subjected to fluctuations in the surrounding ambient air temperature. The fluid properties of the test medium were confirmed to be stable using the UKAS standard reference instrumentation.

    Previous temperature effects research for Coriolis meters have focussed on the process fluid temperature and there is little published data on the effects of ambient temperature.

    Authors: Gordon Lindsay, Norman Glen, John Hay, Seyed Shariatipour, Manus Henry
    Journal: Flow Measurement and Instrumentation
    Volume 73, June 2020, 101754

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  • Thermodynamic and Transport Properties of Hydrogen Containing Streams

    Dr Edris Joonaki,June 2020, Nature Scientific Data

    The use of hydrogen (H2) as a substitute for fossil fuel, which accounts for the majority of the world’s energy, is environmentally the most benign option for the reduction of CO2 emissions. This will require gigawatt-scale storage systems and as such, H2 storage in porous rocks in the subsurface will be required. Accurate estimation of the thermodynamic and transport properties of H2 mixed with other gases found within the storage system is therefore essential for the efficient design for the processes involved in this system chain. In this study, we used the established and regarded GERG-2008 Equation of State (EoS) and SuperTRAPP model to predict the thermo-physical properties of H2 mixed with CH4, N2, CO2, and a typical natural gas from the North-Sea. The data covers a wide range of mole fraction of H2 (10–90 Mole%), pressures (0.01–100MPa), and temperatures (200–500K) with high accuracy and precision. Moreover, to increase ease of access to the data, a user-friendly software (H2Themobank) is developed and made publicly available.

    Author: Dr Edris Joonaki (co-author)
    Journal: Nature Scientific Data

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

    Emmelyn Graham01 June 2020, Journal of Flow Measurement and Instrumentation

    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.

    Author: Emmelyn Graham
    Journal: Journal of Flow Measurement and Instrumentation
    01 June 2020

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  • High frequency pressure loss measurements of laminar-turbulent transitional flow

    Dr Chris Mills, August 2020, Journal of Flow Measurement and Instrumentation

    This paper presents a method for identifying, via pressure measurements at frequencies ranging from 10 Hz–142 Hz, laminar-turbulent transitional flow. The fluctuations in pressure can be successfully used as a diagnostic to infer whether the flow is fully laminar, turbulent or transitioning between the two defined regions. The critical Reynolds number of a flow can be determined from the diagnosis of the pressure loss data at high-frequency when monitored with respect to time. With sufficient resolution of the data, the swift movement between laminar and turbulent flow can be witnessed.

    Author: Dr Chris Mills
    Journal: Journal of Flow Measurement and Instrumentation
    01 August 2020

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Submitted Pre-Print 

  • Influence of Flow Disturbances on Measurement Uncertainty of Industry-Standard LNG Flow Meters

    Dr Asaad Kenbar and Dr Menne Schakel, June 2020

    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/hr and provisional mass flow measurement uncertainty of 0.30% (k = 2) using liquid nitrogen as the calibration fluid. This facility enabled the work described in this paper 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 acknowledgement section) with water and liquid nitrogen (LIN) under various test conditions are fully described in this paper. 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). This was the case for about 85% of the LIN test results.

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