1、 Engineering Technical Note Prepared by the AGA Operating Section Distribution Measurement Committee 400 N. Capitol St., N.W., 4thFloor Washington, DC 20001 U.S.A. Phone: 202-824-7000 Fax: 202-824-7082 Web site: www.aga.org Fluidic Oscillation Measurement for Natural Gas Applications Copyright 2005
2、American Gas Association All Rights Reserved Catalog No. XQ0503 September 2005 iiTABLE OF CONTENTS TABLE OF CONTENTS iii DISCLAIMER AND COPYRIGHT.v ACKNOWLEGDEMENTvi ABSTRACT.vii 1 INTRODUCTION.1 1.1 Task Group Scope 1 1.2 Engineering Technical Note Scope 1 2 PRINCIPLE OF OPERATION.2 2.1 Introductio
3、n 2 2.2 Theory of Fluidic Oscillation Measurement.2 2.2.1 Oscillation Principle 2 2.2.2 Flow Tranquilizer 2 2.2.3 Jet Formation Nozzle. 3 2.2.4 The Coanda Effect . 3 2.2.5 Oscillation Chamber 3 2.2.6 Reynolds Number Relationship 4 2.2.7 Characterization 5 2.2.8 Sensing Method 6 3 METER CONSTRUCTION
4、7 3.1 General 7 3.2 Body 7 3.3 Sensing Elements .7 3.4 Electronics7 4 PERFORMANCE CHARACTERISTICS .8 4.1 Meter Error and Uncertainty 8 4.2 Meter Performance Curve 8 4.3 Pressure Loss8 4.4 Maximum Flow Rate8 4.5 Minimum Flow Rate and Rangeability 8 4.6 Pulsation Effects.9 4.7 Meter Endurance 9 5 UNCE
5、RTAINTY ANALYSIS AND METER ERROR.10 6 INSTALLATION REQUIREMENTS 11 6.1 Piping Configuration 11 6.2 Sizing Considerations.11 6.3 Pressure and Temperature Measurements 11 6.4 Contamination Strainers and Filters 11 6.5 Over-Range Protection .12 6.6 Bypass 12 6.7 Vibration 12 6.8 Orientation12 6.9 Pulsa
6、tion 12 6.10 Gas Composition 12 iii7 FIELD CHECKS.14 7.1 General 14 7.2 Transfer Proving.14 7.3 Differential Pressure Measurement Verification14 7.4 Meter Diagnostics.15 8 CALIBRATION17 9 RECOMMENDATIONS18 9.1 Industry 18 9.2 Users 18 9.3 Manufacturers.18 9.4 Researchers.18 10 APPENDICES .19 Appendi
7、x A OIML Disturbance Test Piping 21 Appendix B Reference Literature25 Appendix C Fluidic Oscillation Measurement Use in the Water Distribution Industry .26 Appendix D Uncertainty Analysis of Fluidic Oscillation Meters .27 FORM FOR SUGGESTION TO CHANGE 31 ivDISCLAIMERS AND COPYRIGHT The American Gas
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18、rm for Suggestion to Change AGA Engineering Technical Note on Fluidic Oscillation Measurement - Natural Gas Applications“ and sending it to: Operations Rich Dewar, Actaris US Gas; Edward Bowles, Southwest Research Institute; Alex Podgers, American Meter Co.; Chuck Brunson, Actaris US Gas; and Andrew
19、 Carver, Actaris Metering Systems is appreciated. In addition, the following list includes those who provided information for the technical note, reviewed the drafts, offered comments and helped in the writing of this document. Their contributions are acknowledged with thanks. Though every attempt w
20、as made to include in the list everyone who contributed, we sincerely regret if any omissions have occurred. Last Name First Name Organization Camden Terry Vectren Energy Cancilla Philip Dominion Peoples Chun Ed Pacific Gas therefore, there is a theoretical minimum flow rate at which this occurs. Be
21、low this theoretical minimum rate, the gas will simply diffuse into the measuring chamber, passing evenly by both sides of the obstacle. - 4 - -3-2-101230 200000 400000 600000 800000 1000000Reynolds NumberError %error %=(1- (referencevolume)/(metervolume) x100Atm60psia100psia150psiaFigure 2.4 2.2.7
22、Characterization A fluidic oscillator, once characterized, will have an “incremental volume” associated with that meter. The incremental volume is the volume of gas at metering temperature and pressure that is needed to flip the gas jet once and is determined at the time of calibration of the meter;
23、 this incremental volume is the reciprocal of the Meter Factor. The factors that could influence the characteristic incremental volume are dimensional changes in the jet formation nozzle or oscillation chamber that constrain the pressure nodes P1(on either side of the cavity) and P2(as shown in Figu
24、re 2.3). So with no moving parts, these dimensions should be stable with respect to time. - 5 - 2.2.8 Sensing Method SensorsOnce an oscillating fluid flow has been created, its oscillations must be sensed and communicated to some instrument for volume determination. Given todays technology, the most
25、 practical means to achieve this appears to be by converting the oscillations into electrical signals for electronic devices to calculate the volume of gas passing through the meter. The most common methods of detecting fluidic oscillations in gas measurement applications are pressure detection or t
26、hermal sensing. The thermal-detection method, in which a change in the density of the fluid produces a signal, has already been implemented. Thermo-resistive sensors detect the passage of the jet, and this can be accomplished with two elements positioned on either side of the gas jet and, therefore,
27、 subjected to the same conditions. Figure 2.5 shows such an installation. Figure 2.5 The only difference in the signal between the two sensors is the momentary difference in density that each sensor detects due to the different velocities in the gas jet. As the jet deflects toward one of the sensor
28、elements, the density of the fast moving gas will be lower than the density over the other element. In this way, the sensors are able to relay the jet oscillation frequency to the electronic device for purposes of volume determination. - 6 - 3 METER CONSTRUCTION 3.1 General The fluidic oscillation m
29、easurement meter consists of two basic components, the body and the sensing elements. The meter also may include electronics as part of the oscillation sensing system, pulse accumulator, and any volume corrections that are incorporated. 3.2 Body The body and all other parts of the pressure-containin
30、g structures should be designed and constructed of materials suitable for the service conditions for which the meter is rated. The bodys end connections should be designed in accordance with the appropriate flange or threaded-connection standards. The body should be identified to show the following:
31、 1. Manufacturers name. 2. Maximum and minimum capacities in actual volume units. 3. Maximum allowable operating pressure. 4. Serial Number. 5. Date of manufacture. 6. An arrow indicating the direction of designed flow. 3.3 Sensing Elements The fluidic oscillation meter is designed to establish an o
32、scillating gas jet that is stable within the conditions specified. This can be accomplished by specifying those conditions and through the design and geometry of the meter body, but a means must be provided to detect and communicate the oscillations to a pulse accumulator/volume totalizer device. Th
33、e actual technology of the sensing elements will depend on the manufacturers design, but the elements should be suitable for natural gas application without causing any adverse effects. A technology currently in use involves a pair of thermal sensors to detect the “swing” of the oscillation. This me
34、thod appears very conducive for a system having its own electronics for sensing and volume totalizing. Finally, depending on the particular sensor technology adopted in the meter, it may be possible to monitor the sensor performance for possible degradation due to contaminant buildup on the surface.
35、 3.4 Electronics The metrological function of a fluidic oscillation device is in the physical portion of the meter, and once the meter has been characterized, the electronics would have only a signal detection and volume- totaling function. The meter electronics also could carry out a diagnostic fun
36、ction, which would verify the operation of the meter and have the ability to report alarm conditions. The integration of volume correction, communications, data-logging, etc., within the meter should become a viable option as technology improvements occur, providing there is a level of integration t
37、hat ensures no loss of data between the separate functions. - 7 - 4 PERFORMANCE CHARACTERISTICS 4.1 Meter Error and Uncertainty Manufacturers specify upper and lower limits for the flow error within which the fluidic oscillation meter should operate. The upper and lower limits may be functions of th
38、e flow rate, the meter installation conditions, or the gas conditions and typically will allow more error near the lower end of the meters operating range. 4.2 Meter Performance Curve The meter error at a given flow rate can be determined from a meter performance curve, which is produced by calibrat
39、ing the meter against a standard (prover) at several different flow rates, then plotting the percent error in flow reading versus the prover flow rate. The resulting error curve can be plotted against the prover flow rate or Reynolds Number, depending on the intended purpose of the curves. In additi
40、on, plots may be used to quantify a meters Repeatability and the meters Reproducibility characteristics, as needed by the meter user and as described in Appendix D. The total uncertainty or the “Expanded Uncertainty” (see NIST TN-1297) then can be produced by incorporating these characteristics (tur
41、n-off turn-on or day-to-day Reproducibilities) with the appropriate ones associated with the calibration facility or prover. When plotted against prover flow rate, the meter performance curves, at various pressures and temperatures, are generally a family of distinctive curves. A useful method is to
42、 produce the meter factor corrected to standard reference conditions and plot these against the Reynolds Number. When the meter error is plotted against the Reynolds Number, meter performance curves tend to show the effects of dynamics including flow profile effects. 4.3 Pressure Loss As with any me
43、ter that obstructs the gas flow, a fluidic oscillation meter is a restriction in the piping system, and will cause a pressure drop proportional to the meters flow rate. With no moving parts, the high flow and pressure drop will not damage the fluidic oscillation meter, but they may produce undesirab
44、le low outlet pressure for the downstream system. Manufacturers product literature for pressure drop information should be consulted when sizing the meter. 4.4 Maximum Flow Rate The maximum flow rate (or maximum capacity rating) for a fluidic oscillation meter is the highest flow rate at which the m
45、eter will operate within some specified certainty or error limit. Depending on the oscillation sensing method, the maximum flow rate of the meter also could be limited by the capability of the sensors. The maximum flow rate typically remains the same for all pressures and temperatures within the sta
46、ted meter operating range. The maximum flow rate also can be expressed in terms of a “standard” flow rate by making the appropriate pressure, temperature, and compressibility corrections. 4.5 Minimum Flow Rate and Rangeability The minimum flow rate (or minimum capacity rating) for a fluidic oscillat
47、ion meter is the lowest flow rate at which the meter will operate within some specified certainty or error limit. Obviously, the - 8 - minimum flow rate depends on the uncertainty limit chosen. Usually, this uncertainty limit is set at 2.0% error. Generally the minimum flow rate is a function of (1)
48、 obtaining a minimum Reynolds Number (as discussed in Section 2.2.6), and (2) the ability of the oscillation sensors to detect the presence of the jet. The minimum flow rate also can be expressed in terms of a “standard” flow rate by making the appropriate pressure, temperature, and compressibility
49、corrections. 4.6 Pulsation Effects While pulsation effects typically seen in distribution measurement applications are negligible, pulsation cannot be ignored when meters are installed in series and in close proximity to a pulsation source. Significant pulsation effects at certain resonances may adversely affect the accuracy. This is particularly true of non-positive displacement meters (e.g., ultrasonic, turbine, or fluidic
