BS 5857-1 2-1980 Methods for measurement of fluid flow in closed conduits using tracers - Measurement of water flow - Constant rate injection method using non-radioactive tracers《密.pdf

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1、BRITISH STANDARD BS5857-1.2: 1980 ISO2975-II: 1975 Methods for Measurement of fluid flow in closed conduits, using tracers Part 1: Measurement of water flow Section 1.2 Constant rate injection method using non-radioactive tracers ISO title: Measurement of water flow in closed conduits Tracer methods

2、 Part II: Constant rate injection method using radioactive tracers UDC 532.542:532.574.87 CONFIRMED JANUARY 2008BS5857-1.2:1980 This BritishStandard, having been prepared under the directionof the Industrial-process Measurementand Control Standards Committee, waspublished under theauthorityofthe Exe

3、cutiveBoardand comesintoeffecton 31March1980 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference PCL/2 Draft for comment77/28087DC ISBN 0 580 11247 0 Cooperating organizations The Industrial-process Measurement and Control Standards Committee, under whos

4、e direction this BritishStandard was prepared, consists of representatives from the following Government department and scientific and industrial organizations: British Gas Corporation British Industrial Measuring and Control Apparatus Manufacturers Association British Steel Corporation CBMPE (Counc

5、il of British Manufacturers of Petroleum Equipment) Control and Automation Manufacturers Association (BEAMA) Department of Industry (Computers Systems and Electronics) Electrical, Electronic, Telecommunications and Plumbing Union Electricity Supply Industry in England and Wales* Electronic Engineeri

6、ng Association Engineering Equipment Users Association* Institute of Measurement and Control Institution of Electrical Engineers Institution of Gas Engineers Oil Companies Materials Association Post Office Engineering Union Scientific Instrument Manufacturers Association Sira Institute The organizat

7、ions marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this BritishStandard: Department of Energy (Gas Standards) UnitedKingdom Atomic Energy Authority Amendments issued since publication Amd. No. Date

8、 of issue CommentsBS5857-1.2:1980 BSI 12-1999 i Contents Page Cooperating organizations Inside front cover National foreword ii 0 Introduction 1 1 Scope and field of application 1 2 Principle 1 3 Required conditions 2 4 Choice of measuring length 3 5 Procedure 4 6 Errors in flow rate measurement 5 7

9、 Analysis methods presently used for water flow rate measurement 6 Figure Determination of the duration of injection 3BS5857-1.2:1980 ii BSI 12-1999 National foreword This BritishStandard has been prepared under the direction of the Industrial-process Measurement and Control Standards Committee, and

10、 is identical with ISO2975-II:1975 “Measurement of water flow in closed conduits Tracer methods Part II: Constant rate injection method using non-radioactive tracers” published by the International Organization for Standardization (ISO). Terminology and conventions. The text of the International Sta

11、ndard has been approved as suitable for publication, without deviation, as a BritishStandard. Some terminology and certain conventions are not identical with those used in BritishStandards; attention is especially drawn to the following. The comma has been used throughout as a decimal marker; in Bri

12、tishStandards it is current practice to use a full point on the baseline as the decimal marker. Wherever the words “International Standard” appear, referring to this standard, they should be read as “BritishStandard”. A British Standard does not purport to include all the necessary provisions of a c

13、ontract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to13 and a back cover.

14、This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS5857-1.2:1980 BSI 12-1999 1 0 Introduction This International Standard is the second of a series of standards covering tracer method

15、s of water flow measurement in closed conduits. The complete series of standards will be as follows: Part I: General; Part II: Constant rate injection method using non-radioactive tracers; Part III: Constant rate injection method using radioactive tracers; Part IV: Integration (sudden injection) met

16、hod using non-radioactive tracers; Part V: Integration (sudden injection) method using radioactive tracers; Part VI: Transit time method using non-radioactive tracers; Part VII: Transit time method using radioactive tracers. 1 Scope and field of application This International Standard specifies the

17、constant rate injection method using non-radioactive tracers for the measurement of water flow rate in closed conduits. 2 Principle Flow rate measurement by a constant rate injection method is based on a comparison between the concentration C 1of a tracer, continuously introduced with a known volume

18、 rate of flow q, and the concentration of samples C 2taken at some place beyond the mixing distance. The mixing distance is defined as the shortest distance at which the variation in concentration of the tracer over the cross-section is less than some pre-determined value (for example:0,5%). (See cl

19、ause6 of partI.) The tracer rate at the injection point is equal to the rate at which it passes the sampling point: q C 1 + Q C 0 =(Q + q) C 2 where C 0is the initial concentration in the stream which is flowing at the rate Q. Hence: Generally C 1is much greater than C 2which leads to a simplificati

20、on of equation(1) as follows: When C 2is much greater than C 0 , the equation can be reduced still further to Flow rate Q can thus be determined by comparing the concentration of the injected solution with the concentration of samples removed from the conduit. In order to increase the accuracy it is

21、 recommended that the standard solution be prepared to a given dilution ratio N stwhich shall be approximately equivalent to the dilution ratio N which is expected in the sample taken from the measuring cross-section. The standard solutions and the samples taken from the measuring cross-section shal

22、l be compared using identical methods, and the following formula is applicable: The flow rate to be determined can be found from the formulaBS5857-1.2:1980 2 BSI 12-1999 3 Required conditions 3.1 Tracer For the constant rate injection method the tracer shall meet the general requirements defined in5

23、.1 of partI. A list of generally used tracers is given in5.1.1 of part I and their advantages with respect to the radioactive tracers are stated in5.2.1.3 and with respect to other non-radioactive tracers in5.2.2 of part I. 3.2 Duration of injection The duration of injection shall be such that stabl

24、e concentration conditions are established at all points of the measuring cross-section over a sufficient period of time. Constant concentration shall be obtained for a period of at least several minutes. A suitable duration of injection may be determined by a preliminary investigation involving the

25、 instantaneous injection of a dye such as fluorescein or a radioactive tracer. Curves1 and2 of the Figure may be plotted for a given flow rate from the observation of the moment when the tracer (dye or activity) appears and disappears in each cross-section. If it is required to achieve steady condit

26、ions for a period of time%t in a selected measuring cross-section S, it is sufficient to add this period of time%t to the time t 1corresponding to the disappearance of the tracer at this point (i.e.on curve2) and to plot through the resulting point C a curve1 parallel to curve1 characteristic of the

27、 appearance of the dye (or activity). The ordinate at the origin of this curve gives the duration of the injection to obtain a concentration level of duration%t at cross-section S. In practice, to obtain a concentration level of duration%t at cross-section S, a calculation is made of the minimum req

28、uired period of injection by adding to the value of%t the time t 2 =AB taken by the instantaneously injected tracer to pass throughS. The time interval t 1between the beginning of the injection and the establishment of stable conditions can be read from curve2 (ordinate of point B) and is directly o

29、btained by measuring the time interval between the instantaneous injection and the tracer disappearance in cross-section S. In the case of central injection, straight measuring length and turbulent flow, time t 2 =AB may be estimated from the relationship The fraction of maximum concentration remain

30、ing after time t 2as given by this formula is0,3%. It is possible, when no preliminary injection is made, to check the appearance of the concentration level, and therefore the minimum injection time, by taking samples and analysing them during the measurement, with the apparatus used for the measure

31、ment. This procedure enables the concentration variation to be determined as a function of time. where U is the mean velocity of the flow; X is the distance to the injection point; D is the conduit diameter.BS5857-1.2:1980 BSI 12-1999 3 4 Choice of measuring length 4.1 Mixing distance The mixing dis

32、tance is defined in6.1 of part I and may be calculated theoretically according to6.2.1 of partI. Figure 3 of part I indicates the measured variation of the actual mixing distance according to the required accuracy in the case of a central injection, and in the case of three other injection methods.

33、Methods for reducing the mixing distance are described in6.3 of part I. 4.2 Experimental checking It is seldom possible in conduits to check experimentally the homogeneity of the mixture and the duration of the tracer passage resulting from an instantaneous injection in a large number of cross-secti

34、ons. In practice, therefore, the experimentation consists of a) determining the minimum period of injection in the measuring length chosen by a preliminary test (see3.2); b) checking, where possible, at the time of the measurement, that the mixture is homogeneous, by taking samples from at least two

35、 points of the measuring cross-section. In the case of high accuracy measurements (for example0,2%), it is necessary to check the homogeneity of the mixture, prior to the measurement itself, when a doubt exists on the quality of this mixture; c) studying, whenever possible by taking samples from ano

36、ther cross-section further downstream, whether there are any systematic differences between the mean concentrations at the two measuring cross-sections. In particular, this method permits verification that the injected tracer is not absorbed in the measuring length either by entrained products in th

37、e liquid or by the conduit walls. 1) 4.3 Losses and additions The losses and additions of the same liquid as that in the measuring length do not affect the results provided certain conditions are met as described in6.5.1 of part I. Figure Determination of the duration of injection 1) See5.1 of part

38、I.BS5857-1.2:1980 4 BSI 12-1999 5 Procedure 5.1 Preparation of the concentrated solution It is essential for the injected solution to be homogeneous. The homogeneity of the solution can be obtained by vigorous mixing, by means of a mechanical stirrer or a closed circuit pump. It is advisable to prep

39、are the injection solution in a separate container from the supply container with water filtered using an appropriate procedure. However, if mixing is carried out in the supply container, the latter shall have sufficient capacity so that it is not necessary to add liquid or tracer during the injecti

40、on. The solution shall be taken at a certain level above the bottom of the container, and every precaution shall be taken so that undissolved particles of the tracer are not carried in the solution injected. In the case of an injection of long duration, provision shall be made as required to avoid a

41、 variation of the solution concentration with time (for example by evaporation under the influence of ambient temperature). 5.2 Injection of the concentrated solution The concentrated solution shall be injected into the conduit at a constant rate and for a sufficient duration to ensure a satisfactor

42、y period of constant concentration at the measuring cross-section (see3.2 and4.2). Several devices may be used for the injection of the concentrated solution. For all devices it must be possible to check the following: that the injection system is always free from leaks; that the injection rate is c

43、onstant over the whole injection duration. To this end, any entrained impurities which may be contained in the solution shall be eliminated as they could partly or totally block the injection circuits. One of the possible devices is a positive displacement pump driven by a constant speed motor. 5.3

44、Measurement of injection flow rate The accuracy with which the injection rate can be measured depends on the measuring instruments used. The accuracy of the device shall be taken into account in the estimation of the total error on flow measurement. Various measuring devices can be used provided the

45、y comply with one of the following requirements: a) they satisfy a principle based on the measurement of the basic quantities of mass, length, time, directly involved in the definition of the quantity of flow; b) they are calibrated in the conditions of use by measuring basic quantities involved in

46、the flow rate definition (for example calibrated capacity method weighing method, etc.); c) they are installed and used in conformity with the requirements of a Standard making it possible to calculate the accuracy obtained. In the case of high accuracy measurements (for example0,2%), it is necessar

47、y to measure the injection rate in accordance with itemsa) orb). The various devices may either give instantaneous values of the injection rate or allow the computation of one or several average values during the injection period. 5.3.1 Among the devices satisfying the first requirement, positive di

48、splacement pumps or calibrated tanks can be mentioned. The former shall preferably be driven by an electric synchronous motor and the constancy of discharge checked by measuring the frequency of the electrical supply. The use of the level drop in a tank as a measurement of the average flow rate requ

49、ires that the tank be calibrated according to the permissible rules provided for this type of operation. If the dimensions of the tank are measured to estimate the capacity, care shall be taken that no deformation occurs during filling and that horizontal areas are measured over a sufficient number of sections to determine the relationship between height and volume with an error consistent with the required accuracy of flow rate. Another method of calibration consists of determining the relationship between the height and the volume by mea