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1.
The compressibility of fluids in a Coriolis mass flowmeter can cause errors in the meter’s measurements of density and mass flow rate. These errors may be better described as errors due to the finite speed of sound in the fluid being metered, or due to the finite wavelength of sound at the operating frequency of the meter. In this paper, they are investigated theoretically and calculated to a first approximation (small degree of compressibility). The investigation is limited to straight beam-type (and does not consider shell-type) Coriolis meters. A lumped-parameter (coupled oscillator) model is used to explain the process causing the errors, and a simple 2-D continuum mechanics model is used to derive expressions for the magnitudes of the errors. Applications might be to Coriolis metering of gases, or to two-phase mixtures in the form of aerated liquids.  相似文献   

2.
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%.  相似文献   

3.
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 NEL'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 NEL's 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.  相似文献   

4.
A lumped parameter, aeroelastic model of Coriolis mass flow and density meters is presented which addresses the effects of compressibility and inhomogeneity introduced by aerated fluids. The model addresses U-tube Coriolis meters containing radially outward and inward flows of a aerated fluid. The mass flow rate and density of the fluid measured by the Coriolis meter are given by solution of an eigenvalue problem governing the dynamics of the aeroelastic system. Mass flow is determined by the phase lag between the displacement of the out-bound and in-bound tubes in the lowest frequency bending mode of the system. Fluid density is related to the natural frequency of this mode.The aerated fluid is assumed to be a well-mixed, dispersed bubbly flow in which the bubbles are small compared to the diameter of the tube. Under this assumption, the effects of compressibility can be incorporated using a lumped parameter model of the first acoustic cross mode of the tube. The effects of inhomogeneity introduced by the bubbles are incorporated using a lumped parameter model of a bubble in a oscillatory acceleration field contained in an viscous, incompressible fluid. The resulting aeroelastic equations of motion for the Coriolis meter show that the behavior of the system is influenced by non-dimensional parameters characterizing the aerated mixtures including reduced frequency, void fraction, and fluid viscosity parameters.The model is used to examine the effect of aeration for a range of parameters considered to be broadly representative of the commercially available Coriolis meters. Results show that aeration can significantly influence the aeroelastic behavior of Coriolis meters, but that, if appropriately considered, Coriolis meters can be used to provide accurate characterization of aerated fluids.  相似文献   

5.
The last ten years have seen an increasing use of Coriolis flowmeters in the measurement of small flows of liquids. The performance of Coriolis meters under pulsating flow conditions was not well known, however. This paper presents some investigations on such flowmeters in the presence of monofrequent and polyfrequent pulsating flows. The linearity of the flow characteristics is checked mathematically and the mechanical resonances of the measuring tubes are determined. Two U-tube type Coriolis meters are tested and the measuring error resulting from the pulsation of the flow is examined. The investigations are carried out with monofrequent pulsation by a special test rig flow and with geared and piston type pumps (polyfrequent excitation).  相似文献   

6.
This paper discusses Small Volume Provers (SVPs), used in the oil and gas industry to validate the performance of custody transfer meters. Recently Coriolis mass flow meters have been introduced for custody transfer; while these offer reduced maintenance requirements over traditional PD and turbine meters, proving Coriolis flow meters using SVP is challenging. This paper presents SVP results for a Coriolis meter which matches or exceeds the most stringent requirements for custody transfer. This is achieved in part by using a novel signal processing technique which reduces the dominant component of the measurement noise, associated with so-called Coriolis mode vibration, with negligible loss of dynamic response.  相似文献   

7.
Coriolis mass flow measurement of gas under normal conditions   总被引:2,自引:0,他引:2  
This paper presents a new method of directly measuring the mass flow of gas using the well-known Coriolis principle, which has proved successful for mass flow measurement of liquids. The prototype consists of two U-shaped tubes, forming a device resembling very much a tuning fork, which is stimulated by electromagnetic actuators to perform autonomous bending oscillations. By this means the fluid is subjected to a radial velocity that, in combination with the axial velocity of the flow, induces harmonic Coriolis forces of the same frequency. This causes the U-shaped tube to perform torsional oscillations that superimpose on the bending oscillations. Both oscillations can be detected via electromagnetic transducers.

The amplitude of the torsional oscillation induced by the Coriolis forces is very small as the density of gas is very low. It can be amplified by tuning the eigenfrequencies of torsion and bending in a control loop. This results in an amplification of the torsional amplitude by a factor of 102, allowing the mass flow of gas to be measured under normal conditions.  相似文献   


8.
In recent years, the Coriolis mass flow meters (CMF), devices based on the Coriolis effect over a vibrating pipe, have developed better metrological performance and they are now a reasonable alternative for the custody transfer measurements. Nowadays, many custody transfer operations require measurement of the net volume (volume measured at a certain reference temperature) and, therefore, it is not feasible to use the CMF as a mass flow meter. However, the actual CMF can be used as net volume meters because they have special equipment to measure density and temperature, and a flow computer. In this work, firstly a mathematical simplification of the physical model is proposed for the CMF. We part from the dimensional analysis of the flow-phase relationship produced by the Coriolis force, the main physical principle behind these devices. A simplified formula is obtained and it permits identifying the magnitudes of influence of the CMF as a mass meter. Secondly, its metrological properties are characterized. For such purpose, a 4” straight tube commercial meter has been calibrated in volume, in the 50 to 165 m3/h range against a standard container and a bidirectional prover, employing gas oil and kerosene (JET-A1). These calibrations have turned out to be compatible with the ones performed by the manufacturer in mass and using water. Then it is verified that the CMF fulfills the requisites of the legal metrology: maximum error allowed, linearity and repeatability. Skewness is observed in the relative error (expressed in %) of the CMF and it has been researched to be due to systematic effects related to constructive parameters of the meter. Lineal correlation is verified between relative error and temperature, and between relative error and flow rate, with negative slopes of −0.03% °C−1 and −0.001% h/m3 respectively.  相似文献   

9.
Coriolis mass flow meters provide accurate measurement of single-phase flows, typically to 0.2%. However gas–liquid two-phase flow regimes may cause severe operating difficulties as well as measurement errors in these flow meters. As part of the Sensor Validation (SEVA) research at Oxford University a new fully digital coriolis transmitter has been developed which can operate with highly aerated fluids. This paper describes how a neural network has been used to correct the mass flow measurement for two-phase flow effects, based entirely on internally observed parameters, keeping errors to within 2%. The correction strategy has been successfully implemented on-line in the coriolis transmitter. As required by the SEVA philosophy, the quality of the corrected measurement is indicated by the on-line uncertainty provided with each measurement value.  相似文献   

10.
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.  相似文献   

11.
Entrained gas has been regarded as disturbance to measurements based on Coriolis meters, since measurement accuracy can be degraded because of this disturbance. Recent research from Endress + Hauser has discovered that different types of gas bubbles, namely free bubbles and suspended bubbles, have various impact on the meter measurement performance. It is important to understand the error mechanism for different effects, namely bubble effect and resonator effect, which are introduced by different bubble types, and to take the corresponding measures to cope with the effects. It is also crucial to identify the bubble pattern in the measuring tube of a Coriolis meter to make a diagnosis and reduce the negative influence of the disturbance accordingly. For free bubbles that typically cause inhomogeneity of a medium, the fluctuation of the resonance frequency of the measuring tube in a Coriolis meter is directly correlated to the existence of this type of bubbles, since this medium under a flowing condition causes density fluctuation to the meter as gas density is typically much lower than that of a liquid. For homogenous suspended bubbles that lead to a significantly increased compressibility of a medium, the innovative Multi-Frequency Technology in Promass Q sensor offers the means to qualitatively detect the existence of this type of bubbles and quantitatively calculate the volume fraction of the gas phase, based on its ability to derive the speed of sound in a medium containing such bubbles. Identification of the type of bubbles helps not only for crediting the measurement reliability, but also for obtaining more detailed medium properties, and in turn a better process insight, with which a process optimization can be enabled to improve the quality of production.  相似文献   

12.
Metering on gas-liquid two-phase flow is challenging even though the Coriolis Mass Flowmeters (CMFs) outperform most of other flow measurement technologies owing to their ability to directly measure the fluid mass flowrates. This is due to complexity of the dynamics of the gas-liquid two-phase flow. Thus, Coriolis Mass Flowmeters have been undergoing modifications to improve their accuracy on measuring complex flows but still the variation of error due to bubble entrainment and the mechanisms responsible of these errors remain less understood. Hence there is a strong need to conduct further characterization on the performance of CMFs on measurement on gas-liquid two-phase flow.This study aims to analyse the performance of a U-shape CMF on metering gas-liquid two-phase flow via both CFD simulation and experimental measurements. For simulation, a two-way coupling of Fluid-Structure Interaction was used to minimize the inaccuracy in simulation results. It has the ability to count on influences of fluid forces on the tube deformation and the reaction of the oscillating-fluid conveying tube to the overall dynamics of the system.The results show that at low nominal flowrates (NFRs), the flow/phases separation occurs and dominates the previously identified factors of errors such as bubble theory effect/friction damping effect and cause positive errors. The error associated with bubble theory effect or friction damping is negative i.e. the CMFs under-estimate the mass flowrates of the mixture. Our study, however, found negative errors only at high nominal mass flowrates. In addition, it is to be noted also that even though the theoretically predicted error due to mixture compressibility in some literatures could be positive, it is important to carry out further experimental and computational studies for analysis. In this study, it is observed that the oscillations of separated fluid phases amplify the amplitude of tube oscillation and hence leading to distortion of the displacements of the CMF tube. This could lead to up to 14.9% of positive error in CMFs’ measurements at the low nominal mass flowrates.It is believed that these results can serve as baselines for future studies on corrections and compensations of CMFs’ errors on measurement on gas entraining fluid flow encountered in fuel bunkering and LNG metering processes.  相似文献   

13.
The use of Coriolis mass flow metering for two-phase (gas/liquid) flow is an emerging theme of both academic research and industrial application. The key issues are maintaining flow-tube operation, and modelling and correcting for the errors induced in the mass flow and density measurements. Experimentally-derived data is used to illustrate that these errors vary most notably with gas void fraction (GVF) and liquid flow rate, but other factors such as flow-tube geometry and orientation, and fluid properties such as viscosity are also influential. While undoubtedly a universal two-phase flow correction model is the ultimate research goal, there is currently no obvious candidate to explain the range of behaviours observed. This paper describes and demonstrates an empirical methodology that has proven effective in developing good correction models for a given choice of Coriolis flow-tube and flow mixture.

A growing proportion of the world’s oil reserves may be described as “heavy”, implying high density and high viscosity. Of the various metering challenges heavy oil poses, one of the most significant is its ready entrainment of gas, and the difficulties entailed in separating gas from the oil. Accurate two-phase measurement of heavy oil is therefore an especially desirable technical goal.

Trials were carried out at the National Engineering Laboratory (NEL), Scotland on a 75 mm flowmeter using a high viscosity oil. Flowrates from 1 kg/s to 10 kg/s were examined, with gas void fraction (GVF) up to 80%. The resulting models were tested online in a commercial Coriolis mass flow meter and demonstrated good performance for both steady and slugging two-phase flows, with the corrected measurements typically within 1%–5% of the nominal mass flow and density.

Field trials in Venezuela have confirmed the performance of this two-phase solution.

While research continues into the development of a generic two-phase correction, this case study demonstrates that the current state of the art can provide, for economically important fluids, tailored models with good two-phase flow performance.  相似文献   


14.
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.  相似文献   

15.
The paper identifies the requirements for both a Coriolis flow-tube and the associated flow-transmitter, to achieve an ultra-fast dynamic response. A ‘new’ meter was assembled using a commercially available straight flow-tube, selected for its high drive (fundamental resonant) frequency of about 750 Hz (water-filled) and this was interfaced with a newly extended version of Oxford’s digital transmitter technology. This new transmitter gives measurement updates that are calculated every half drive-cycle, at 1.5 kHz, and are output via a high precision frequency pulse signal. Dynamic response tests in the laboratory and during a field trial have shown the ‘new’ meter to have a response time at least an order of magnitude faster than was reported previously [Clark C, Cheesewright R. Experimental determination of the dynamic response of Coriolis mass flow meters. Flow Measurement and Instrumentation 2006;17:39–47] from tests on the fastest response commercially available Coriolis meters. The ‘new’ meter shows a typical delay of 3.8 ms between a change in fluid flow rate and the corresponding change in the frequency output. Suggested further developments of the new transmitter technology indicate a route that could be followed to produce transmitters suitable for the newly emerging micro-machined Coriolis flow-tubes, which have fundamental resonant frequencies in the range 10–30 kHz.  相似文献   

16.
对流体在科里奥利质量流量计(以下简称科氏流量计)内的扭转运动状况进行了分析,得到运动速度与粘度的关系.通过对弯曲振动运动进行分析,结合流体运动及内摩擦力耗能情况,提出了一种新的粘度检测方法,导出了流体动力粘度与科氏流量计振动参数的关系,通过实验验证了方法的正确性.分析了影响粘度测量精度的部分因素.该方法简单、实用,拓展了科氏流量计的应用领域.  相似文献   

17.
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%.  相似文献   

18.
Effect of fluid pressure on Coriolis mass flowmeter''s performance   总被引:4,自引:0,他引:4  
This paper presents some tests which have been carried out on a commercial model of Coriolis mass flowmeter under medium-pressure conditions (p > 15 bar), utilizing a primary standard flow calibration facility. The experimental results show that the fluid pressure affects the accuracy of the tested meter, which provides underestimated readings (i.e. negative errors). Finally, some diagrams which allow to correct the output signal (or the reading) provided by the tested meter (according to the operating fluid pressure) are also presented.  相似文献   

19.
The problem of computing accurate Coriolis distortion modes in mass flow meters is discussed. This is illustrated by several numerical results, and it is tentatively suggested that the problem is due mainly to computer rounding error rather than any fundamental weakness in the finite element method or the eigensolvers. An empirically evaluated successful method, using a shifted inverse iteration, for computing high quality results is given.  相似文献   

20.
The current status of available work regarding the pressure effect on Coriolis mass flowmeters is reviewed, which shows significant improvement in the latest generation of Coriolis flowmeters. A theoretical method using the linear damping model is proposed to understand the pressure effect. This new method applied to Coriolis flow sensors provides intuitive insight into the flow-generated signal by studying undamped natural frequencies and mode shapes. Most importantly this method can be used to model virtually any shape and configuration of flow sensors as found in the practical design. It is found that when the pressure changes it alters the superimposed contribution and the mass flow measurement can deviate from the reference condition. Experimental results from both low and high pressure flow tests are reported, which are in general agreement with the theoretical prediction. Further specific work is finally suggested which may advance our understanding and improve the Coriolis mass flow measurement technology.  相似文献   

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