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Hakan Kaykisizli, Dr.Vahit CiftCi, Ernur Karadogan, Basak Akselli
PRINCIPLE OF CONVERTING THE MECHANICAL MOVEMENTS TO ELECTRICAL SIGNALS BY TURBINE METERS

Turbine meter is a flow measurement device utilizes the angular velocity of rotating blades to measure the flow rate. Pulses for a known time period are counted by turbine meter counting mechanism. The total number of counts for a given time period is proportional to the volumetric flow rate of the turbine meter. National Metrology Institute of Turkey (UME) standard reference turbine meter pulse information is generated by a system called variable reluctance tachogenerator.
This paper explains how mechanical movements of blades are converted to electrical signals and comparing the degree of conformity between the theoretical and experimental results. Meter factor k is utilised to compare experimental and theoretical results. Geometrical calculations and experimental results from the UME reference turbine meter are compared. Vector analysis of the forces acting on the blades showed that blades are moving slower than their geometrically predicted velocity. This is explained by effect of retarding torques on the exit velocity of the fluid.

E. von Lavante, N. Lazaroski, U. Maatje, T. Kettner, V. Lötz-Dauer
NUMERICAL SIMULATION OF UNSTEADY THREE-DIMENSIONAL FLOW FIELDS IN A TURBINE FLOW METER

The complex three-dimensional unsteady flow field in a one-stage turbine gas flow meter was studied by carrying out numerical simulations using the Navier-Stokes solver Fluent. The simulation of all the viscous effects as well as secondary flows, such as the flow in the tip gap and secondary and tertiary vortices in the blade to blade region required a very high grid resolution. Therefore, a series of three-dimensional block-oriented hybrid grids containing between 300 thousand and 1.5 million grid cells was generated and implemented. The aim of the present project was to find the correct operating conditions to subsequently explain the behavior of the mechanical accuracy of the meter, to prove the correctness of the theory of operation a.nd to verify these results by comparison with experimental measurements.

Kazuto Kawakita
PRACTICAL EXPERIENCE ON INSPECTIONS OF ORIFICE PLATES MEASUREMENT SYSTEMS FOR NATURAL GAS

Everyday, in many countries producers and importers supply larg e volumes of natural gas produced from domestic fields or purchased abroad. To attend to this need, a whole host of interlinked and co- ordinated activities and technical installations are required both on the purchase and the sales side. Besides the production and processing facilities, compression stations, transmission and distribution pipelines, operation and control stations, many measuring systems are necessary to quantify the huge volumes of gas commercialized among parts.
Natural gas measurement sys tems can be found in gas production plants, custody transfer stations, citygates, gas processing units and industrial gas consumers. Due to the commercial aspects involved, in most of these cases, gas deliverers and gas receivers operate its own independent measurement systems, always checking if the differences between both measurements are under the tolerances agreed through detailed contracts.
The main objective of gas measuring stations is to perform accurate and reliable measurements of gas volumes, by use of controlled equipment and recognized metering techniques, which can assure an acceptable level of uncertainty for the measurement and that comply with the national regulations for the gas industry. More complete metering systems are able to measure gas flow in terms of energy flow, the effective product under trade.
Though the thousands of turbine meters in operation and the increasing acceptance of multipath ultrasonic flowmeters in the gas industry, one of the most common measurement principle fo r natural gas still used throughout the world is the orifice plate. It is a traditional and well-known technology which origin goes back to 1779 when Giovanni B. Venturi, an Italian physicist, first conceived a differential pressure type flowmeter.
Some of the main advantages of an orifice plate is that it has no moving parts exposed to wear, and it doesn’t require a calibration of the primary element in a laboratory since the discharge coefficient of an orifice plate can be calculated by empiric relations like the Reader-Harris-Gallagher (RG) equation.
Two of the main disadvantages of the orifice plate is the significant pressure drop and the relatively low rangeability, making it suitable especially for metering stations operating under a relatively low flowrate variation regime and installed in pipelines where a permanent pressure loss is not a critical factor.

A. Saglam, P. M. A. van der Kam, G. J. van Essen, D. H. Hebels
TIME DEPENDENT PERFORMANCE OF TURBINE GAS METERS

Gastransport Services in the Netherlands, uses turbine gas meters to measure the gas flow to local gas distribution companies, large industrial customers and power plants GTS operates approximately 1100 city gate stations, at a delivery pressure of usually 8 bar.
In the Netherlands, the procedures for determining the operational performance of the turbine meters are agreed upon between Gastransport Services and its customers. As a result of this agreement, Gastransport Services inspects the total population of turbine meters by means of the well-known variables-acceptance-sampling. Each year, 60 turbine meters are selected randomly from the total population. Subsequently, the selected turbine meters are calibrated traceable to international standards by Netherlands Measurment Institute (NMi). The information from these recalibrations is used to study the stability of the turbine meters.
Because, through the years a lot of information has been gathered on the turbine meters performance, the presence of statistically significant relationships (correlation) between the performance in time of the meters on the one hand and properties like the construction year, the pressure class, the size, the maximum allowable flow rate and/or the recalibration period of the meter on the other hand, can be investigated. In this presentation, analysis-of-variance and the quadrant-correlation-test are used to test for the presence of such correlations.
The aforementioned five properties were analysed for the presence of correlation at two different calibration pressures and with different definitions of drift to express the performance in time of gas turbine meters. For a specific calibration pressure and a specific type of drift, the performance in time dependents on the recalibration period and the size of the turbine meter. Furthermore, the correlation analysis, showed that a turbine gas meter seems to reach a steady state in time, expressed in terms of shift of the weighted mean error.

E. von Lavante, R. Kramer, B. Mickan
FLOW BEHAVIOR IN SONIC MICRO-NOZZLES

Detailed investigation of flow fields associated with sonic Venturi nozzles with extremely small Reynolds numbers used for flow metering was carried out. The range of Reynolds numbers considered in this work extended from Re = 323 to Re = 452. In the experimental part, global parameters such as discharge coefficient Cd were investigated independently for two different diameters, d = 25 µm and d = 35 µm. Both discovered flow phenomena that were not explainable using simple linear theories. Therefore, in the numerical part of the present investigation, the corresponding flow fields were simulated using compressible viscous flow solvers ACHIEVE and Fluent. The qualitative agreement of the numerical and experimental results was satisfactory; the comparison enabled the authors to explain most of the physical phenomena observed.

Gabriel Moniz Pereira, Bodo Mickan, Rainer Kramer, Dietrich Dopheide, Ernst von Lavante
INVESTIGATION OF FLOW CONDITIONING IN PIPES

It is a well-known and recognised fact that the behaviour of flow rate and volume measuring devices can be affected very strongly by the flow conditions prevailing in their inlet pipe section. Disturbed velocity profiles caused by pipe configurations such as bends, headers, pressure regulators and convergent or divergent pipe sections in front of a flow meter can lead to deviations of the meter reading by up to several percents.
Thus, flow conditioning normally means the generation of fully developed flows in the inlet of meters to avoid installation effects. Since this is in practice not always possible, it is necessary to investigate the influence of flow perturbations to the behaviour of flow meters. Such investigations are normally part of pattern approval in legal metrology. Hence, in case of pattern approval flow conditioning means the generation of disturbed flows with a definite and reproducible level of perturbation. The International Organisation of Legal Metrology OIML defined therefore standard pipe configurations (e.g. in OIML Recommendation R 32) to perform perturbations test within pattern approvals.
The test configurations recommended by OIML were defined for applications in atmospheric air. The main reason for this narrowed view was the huge effort necessary to perform perturbation test under high pressure conditions. In praxis this leads to several problems, mainly if the meter under test (e.g. some ultra sonic meters) works only with high pressure gas or the meter behaviour have strong dependence on Reynolds number or pressure. In the first case the economic effort for pattern approval is very high and only a few test facilities are able to handle such configurations and in the second case it is a very sensitive question to transfer results from low pressure to high pressure conditions.
In this paper some results of investigation in the field of installation effects and flow conditioning done in PTB are shown concerning following points:
- differences of flow conditioning using real pipes under low and high pressure conditions,
- a new concept (perturbation plate) for generating definite disturbed flows which can easily performed under high pressure conditions and
- basic investigations to improve the application of CFD simulations to determine flow profiles from geometry of piping.

Douglas Baumoel
THE DESIGN AND APPLICATION OF CLAMP-ON ULTRASONIC FLOWMETERS FOR CUSTODY TRANSFER AND CHECK METERING GAS APPLICATIONS

Recent advances in externally mounted sensor design and related electronics have enabled gas meters using clamp-on, non-intrusive, ultrasonic transducers to provide performance equal to or better than meters using conventional insert transducer technology. It is acknowledged that this claim will be met with skepticism; however, the following pages provide evidence of this performance capability. This paper also presents the technical challenges to this design, and how they were overcome. We will review the applicability, benefits, and limitations of the various configurations of this technology.

Torbjörn Löfqvist, Kestutis Sokas, Jerker Delsing
SPEED OF SOUND MEASUREMENTS IN GAS-MIXTURES AT VARYING COMPOSITION USING AN ULTRASONIC GAS FLOW METER WITH SILICON BASED TRANSDUCERS

This paper concerns speed of sound measurements performed in three different gas mixtures at constant temperature and pressure while the concentration of the gases was varied. The performed experiments used an ultra sonic, sing-around, gas flow meter equipped with silicon based transducers. The center frequency of the transducers was 800 kHz. Speed of sound was measured in mono-, di- and triatomic gases: argon (Ar), oxygen (O2) and carbon dioxide (CO2), in either air or nitrogen (N2) as a background gas. The gas under investigation was mixed with the background gas in a test chamber and the concentration of the gas under examination was varied between 0% and 100%. A gas chromatograph was used in order to accurately determine the composition of the gas mixture. The experiments show that measured speed of sound, as a function of gas composition, agrees with the speed of sound obtained from theory. The achieved data also show that the speed of sound measurements was performed with low standard deviation. Thus, one can conclude that this type of ultrasonic gas flow meter is well suited in determining gas concentration in a binary gas mixture as well as flow velocity. The technique could be of value in both industrial and medical applications.

Sampo Sillanpää, Martti Heinonen
THE MIKES MEASURING SYSTEM FOR GAS MASS FLOW

Due to the increasing need for traceable gas flow measurements in Finland, the development of a national measurement standard for gas mass flow was initiated at the Centre for Metrology and Accreditation (MIKES) in 2002. A primary calibration system based on dynamic weighing was constructed to provide traceability directly to the national mass and time standards. The MIKES gas flow measuring system includes also a commercial calibrator based on laminar flow elements. It is used as a working standard when calibrating mass flow meters for customers. The calibration range encompasses 0,4 mg / s to 625 mg / s. The relative standard uncertainty of the gravimetric system is between 0,2 % and 0,4 %.

Noel Bignell
EFFECT OF GAS TYPE ON THE THERMAL PROPERTIES OF SMALL SONIC NOZZLES

A previous study (Bignell and Choi, Flow Meas. & Instrum. 13 (2002) 17-22) of the effect of temperature on the coefficient used to characterise small sonic nozzles is reviewed. Adiabatic cooling of the gas stream in the throat causes the body of nozzles to be cooled but a heater and temperature control system allow the temperature of the nozzle to be held constant. Using a gas flow standard that can operate in continuous mode, measurements were made of nozzle coefficients at different temperatures using air, argon, nitrogen and carbon dioxide. The nozzle coefficient changes with the gas type and linearly with the temperature of the body of the nozzle. The first of these changes is explained by changes in the real gas correction factor for argon but not for carbon dioxide. The temperature changes are much greater than those due to the area, the discharge coefficient and the real gas correction factor. It is necessary to invoke the properties of the thermal boundary layer to explain these changes, which are found to be greater for gases having a higher specific heat ratio.

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