BS 5857-1 3-1980 Methods for measurement of fluid flow in closed conduits using tracers - Measurement of water flow - Constant rate injection method using radioactive tracers《密封管道中.pdf

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1、BRITISH STANDARD BS 5857-1.3: 1980 ISO2975-III: 1977 Methods for measurement of Fluid flow in closed conduits, using tracers Part1: Measurement of water flow Section1.3 Constant rate injection method using radioactive tracers ISO title: Measurement of water flow in closed conduits Tracer methods Par

2、tIII: Constant rate injection method using radioactive tracers UDC 532.542:532.574.87:539.16 CONFIRMED JANUARY 2008BS5857-1.3:1980 This BritishStandard, having been prepared under the directionof the Industrial-process Measurement and Control Standards Committee, was published underthe authority of

3、the Executive Board and comesintoeffect on 31March1980 BSI 12-1999 The following BSI references relate to the work on this standard: Committee referencePCL/2 Draft for comment77/28089DC ISBN 0 580 12489 9 Cooperating organizations The Industrial-process Measurement and Control Standards Committee, u

4、nder whose 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 CBM

5、PE (Council 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

6、Engineering 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

7、organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee untrusted with the preparation of this BritishStandard: Department of Energy (Gas Standards) United Kingdom Atomic Energy Authority Amendments issued since publication Amd

8、. No. Date of issue CommentsBS5857-1.3:1980 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 1 4 Choice of measuring length 2 5 Procedure 3 6 Methods of analysis and c

9、omputation 5 7 Choice of radioactive tracers 7 8 Example of calculation of flow rate 8 9 Estimation of error 11 Figure 1 Determination of the duration of injection 3 Figure 2 Error on the mean count rate for a certain number of samples 13BS5857-1.3:1980 ii BSI 12-1999 National foreword This BritishS

10、tandard has been prepared under the direction of the Industrial-process Measurement and Control Standards Committee and is identical with ISO2975-III:1976 “Measurement of water flow in closed conduits Tracer methods PartIII: Constant rate injection method using radioactive tracers” published by the

11、International Organization for Standardization (ISO). Terminology and conventions. The text of the International Standard has been approved as suitable for publication, without deviation, as a BritishStandard. Some terminology and certain conventions are not identical with those used in BritishStand

12、ards; attention is especially drawn to the following. The comma has been used throughout as a decimal marker. In BritishStandards 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 sho

13、uld be read as “BritishStandard”. Additional information. In the table in7.2 the SI unit for concentration is the Bq/cm 3where1Bq=3.7 10 10 Ci. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct appl

14、ication. 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. This standard has been updated (see copyright date) and may have had amend

15、ments incorporated. This will be indicated in the amendment table on the inside front cover.BS5857-1.3:1980 BSI 12-1999 1 0 Introduction This International Standard is the third of a series of standards covering tracer methods of water flow measurement in closed conduits. The complete series of stan

16、dards will be as follows: PartI: General; PartII: Constant rate injection method using non-radioactive tracers; PartIII: Constant rate injection method using radioactive tracers; PartIV: Integration (sudden injection) method using non-radioactive tracers; PartV: Integration (sudden injection) method

17、 using radioactive tracers; PartVI: Transit time method using non-radioactive tracers; PartVII: Transit time method using radioactive tracers. 1 Scope and field of application This International Standard specifies the constant rate injection method using radioactive tracers for the measurement of wa

18、ter 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 rate of flow q, and the concentration of samples C 2taken at some place beyond the dis

19、tance 1) . 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 example0,5%). (See clause6 of part1.) The tracer rate at the injection point is equal to the rate at which it pa

20、sses 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 simplification of equation(1) as follows: When C 2is much greater than C 0 , the equation can be reduce

21、d 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. 3 Required conditions 3.1 Tracer For the constant rate injection method the tracer shall meet the general requirements defined in5

22、.1 of partI. A list of generally used tracers is given in5.1.2 of partI and their advantages with respect to non-radioactive tracers are stated in5.2.1.1 and5.2.1.2. 3.2 Duration of injection The duration of injection shall be such that stable concentration conditions are established at all points o

23、f the measuring cross-section over a sufficient period of time. Constant concentration shall be obtained for a period of at least several minutes. 1) Another method can be contemplated which would not involve sampling. . . . (1)BS5857-1.3:1980 2 BSI 12-1999 Determination of the injection duration A

24、suitable duration of injection may be determined by a preliminary investigation involving the instantaneous injection of a dye such as fluorescein or a radioactive tracer. Curves1 and2 ofFigure 1 may be plotted for a given flow rate from the observation of the moment when the tracer (dye or activity

25、) appears and disappears in each cross-section. If it is required to achieve steady conditions 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)

26、 and to plot through the resulting point C a curve1 similar to curve1 characteristic of the 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 co

27、ncentration level of duration %t at cross-section S, a calculation is made of the minimum required period of injection by adding to the value of %t the time t 2 =AB taken by the instantaneously injected tracer to pass through S. The time interval t 1between the beginning of the injection and the est

28、ablishment of stable conditions can be read from curve2 (ordinate of point B) and is directly obtained 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, t

29、 2 =AB may be estimated from the relationship The fraction of maximum concentration remaining 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 continu

30、ously sampling the flow and measuring its count rate, with the apparatus used for the measurement. This procedure enables the concentration variation to be determined as a function of time. 4 Choice of measuring length 4.1 Mixing distance This is defined in6.1 of partI and may be calculated theoreti

31、cally according to6.2.1 of partI. Figure3 of partI indicates the measured variation of the actual mixing distance according to the required accuracy in the case of central injection and in the case of three other injection methods. Methods for reducing the mixing distance are described in6.3 of part

32、I. where U is the mean velocity of the flow; X is the distance to the injection point; D is the conduit diameter.BS5857-1.3:1980 BSI 12-1999 3 4.2 Experimental checking It is seldom possible in conduits to check experimentally, in a large number of cross-sections, the homogeneity of the mixture and

33、the duration of the tracer passage resulting from an instantaneous injection. 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 measurem

34、ent, that the mixture is homogeneous by taking samples from at least two 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

35、 this mixture; c) studying, whenever possible by taking samples from another 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

36、 not absorbed in the measuring length either by entrained products in the liquid or by the conduit walls. 2) 4.3 Losses and additions The losses and additions of the same liquid as that in the measuring length do not affect results provided certain conditions are met as described in6.5.1 of partI. 5

37、 Procedure 5.1 Handling of radio-isotopes The use of radio-isotopes (storage, transportation, handling) shall comply with any existing statutory regulations. Figure 1 Determination of the duration of injection 2) See5.1 of partI.BS5857-1.3:1980 4 BSI 12-1999 5.2 Preparation of the concentrated solut

38、ion It is essential for the injected solution to be homogeneous. 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 prepare the injection solution in a separate container from the supply container with water f

39、iltered 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 injection. The solution shall be taken at a certain level above the bottom of the container, and

40、 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 variation in time of the solution concentration (forexample by evaporation under the inf

41、luence of the ambient temperature). To minimize possible adsorption effects with the radioactive tracer it is advisable to add to this solution a carrier constituted by a certain amount of non-radioactive substance identical to that containing the radioactive tracer. 5.3 Injection of the concentrate

42、d solution The concentrated solution shall be injected into the conduit at a constant rate and for a sufficient duration to ensure a satisfactory period of constant concentration at the measuring cross-section. The injection may be made by means of a positive displacement pump. It shall be possible

43、to check the following: that the injection system is always free from leaks; that the injection rate is constant over the whole injection duration. 5.4 Measurement of injection rate The measurement of injection rate shall be based on the measurement of the basis quantities of mass, length, time, dir

44、ectly involved in the definition of the quantity of flow. The injection system shall be calibrated before and after the tests. The mean value of injection rate shall be used in the calculation of flow rate provided that the two calibrations do not differ by more than a value consistent with the over

45、all required accuracy of flow measurement (for example1%). When the injection is carried out by means of a positive displacement pump driven by a synchronous motor, which is the normal method, the checking of flow rate consists in fact in the measurement of the frequency of the electrical supply. 5.

46、5 Sampling 5.5.1 Samples Samples shall be taken: from the conduit, to verify that the background concentration of tracer in the flow system is constant; from the conduit, to determine the tracer concentration in the measuring cross-section, to check that the tracer concentration is homogeneous in th

47、e sampling cross-section and to check the concentration level (see4.2); from the injected solution, to check the homogeneity of the tracer concentration (see5.2); from the injection solution, to compare the concentration of tracer in the injected solution with the concentration of tracer in the samp

48、les taken from the conduit. In practice, samples shall be taken under the following conditions: two or three samples of the liquid flowing in the conduit upstream from the injection section during injection or, when variations of the background concentration along the meaning length are suspected, i

49、n the sampling cross-section before and after the passage of the solution; three to five samples of the injected solution at the outlet of the injection equipment immediately before and after the injection period; at least five samples of the diluted solution in the conduit, if possible from at least two points in the measuring cross-section (at least three at the same point), distributed in time during the passage of the solution.BS5857-1.3:1980 BSI 12-1999 5 5.5.2 Sampling equipment Sampling shall be carried out during t