1、 Reference number ISO/TR 9824:2007(E) ISO 2007TECHNICAL REPORT ISO/TR 9824 First edition 2007-04-01 Hydrometry Measurement of free surface flow in closed conduits Hydromtrie Mesurage du dbit des coulements surface dnoye dans les conduites fermes ISO/TR 9824:2007(E) PDF disclaimer This PDF file may c
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6、ht office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2007 All rights reservedISO/TR 9824:2007(E) ISO 2007 All rights reserved iii Contents Page Foreword iv 1 Scope . 1 2 Normative references .
7、 1 3 Terms and definitions. 1 4 Characteristics of a closed conduit system 1 4.1 Physical structure. 1 4.2 Construction 2 4.3 Flow conditions. 2 4.4 Environment 2 5 Selection of method 3 5.1 General. 3 5.2 Factors . 3 6 Methods of measurement 4 6.1 Volumetric methods . 4 6.2 Tracer and dilution meth
8、od . 5 6.3 Flow measurement structures. 6 6.4 Ultrasonic Doppler 17 6.5 Transit time ultrasonic flow meters 18 6.6 Electromagnetic method 21 6.7 Slope-area method 23 6.8 Non-contact methods. 25 6.9 Spot flow measurements, evaluation and verification 26 7 Final selection of method 26 Annex A (informa
9、tive) Guide to the selection of methods. 27 Bibliography . 30 ISO/TR 9824:2007(E) iv ISO 2007 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards
10、 is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take p
11、art in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to
12、 prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. In exceptional circumstances, when a te
13、chnical committee has collected data of a different kind from that which is normally published as an International Standard (“state of the art”, for example), it may decide by a simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely informativ
14、e in nature and does not have to be reviewed until the data it provides are considered to be no longer valid or useful. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all s
15、uch patent rights. ISO/TR 9824 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 1, Velocity area methods. This first edition of ISO/TR 9824 cancels and replaces ISO/TR 9824-1:1990 and ISO/TR 9824-2:1990, of which it constitutes a technical revision. TECHNICAL REPORT ISO/TR
16、 9824:2007(E) ISO 2007 All rights reserved 1 Hydrometry Measurement of free surface flow in closed conduits 1 Scope This Technical Report provides a synopsis of the methods of flow gauging that can be deployed in closed conduits flowing part full, i.e. with a free open water surface. It provides a b
17、rief description of each method with particular reference to other International Standards where appropriate, the attributes and limitations of each technique, possible levels of uncertainty in the flow determinations and specific equipment requirements. The uncertainties quoted herein are expanded
18、uncertainties with a coverage factor of 2 and an approximate confidence level of 95 %. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of
19、 the referenced document (including any amendments) applies. ISO 772, Hydrometric determinations Vocabulary and symbols 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 772 and the following apply. 3.1 free surface flow in closed conduits flow within
20、closed conduits, under the influence of gravity only, and normally having a free surface 4 Characteristics of a closed conduit system 4.1 Physical structure Closed conduits can be located below ground (e.g. sewer) or above ground (e.g. culvert). Systems constructed underground usually incorporate a
21、means of access through a suitable sized shaft (manhole) sealed at the surface with a secure, but removable, cover. Access shafts may be provided at frequent intervals along the length of the conduit. It is normal to locate shafts at points of structural change in the system, such as bends, or junct
22、ions, or where for some reason, inspection or entry to the system may be required. Access will be subject to strict health and safety conditions and operatives may require special training. Also, access may not be allowed during or following a period of rainfall. ISO/TR 9824:2007(E) 2 ISO 2007 All r
23、ights reserved4.2 Construction 4.2.1 Material Conduits can be made from a variety of materials such as dry stone blocks, vitreous clayware, concrete, cast iron, steel, galvanized iron or steel, asbestos and glass reinforced plastic. In addition, the conduit may have been formed out of the natural be
24、drock. The roughness of the surface of the conduit may range from smooth to extremely rough. The roughness may be influenced by organic growths, deposits of sediment, rust, cracks, holes and other imperfections. 4.2.2 Cross-sectional shape Closed conduits are most commonly circular or rectangular in
25、 shape. They may also be ovoid, horseshoe, barrel or triangular. For the purposes of this Technical Report, they are considered to range in diameter from 150 mm upwards. 4.3 Flow conditions Flow in closed conduits can vary from clear water, free from contaminants (e.g. spring flows), to liquids cont
26、aining both floating and suspended material (e.g. foul sewer), and in some cases effluents of a corrosive nature. The fluid itself may be an admixture of several substances each with its own characteristic properties. Discharges may vary over a wide range from reverse flow, through zero to many cubi
27、c metres per second. For some applications, measurement equipment should be capable of withstanding inundation and measuring surcharge flow. The flow, especially that generated from impervious catchments, may exhibit rapid changes in discharge over short durations and may range from subcritical to s
28、upercritical. 4.4 Environment 4.4.1 Within the conduit The atmosphere within a conduit system may be assumed to be in equilibrium with the liquid in the conduit. If the atmosphere is of a toxic and/or corrosive nature, precautions should be taken to protect the equipment from its effects or choose a
29、 method for which this is not a problem. It is possible that under certain circumstances, the atmosphere may be of a potentially highly explosive nature. Therefore, the equipment to be installed within the confines of the conduit system should be intrinsically safe. For example, all electrical circu
30、its should be constructed so that they cannot cause ignition of the atmosphere. The extremes of the atmospheric environment within which the equipment is expected to operate need to be ascertained in terms of temperature, humidity, pressure and gases. 4.4.2 External environment Where elements of the
31、 equipment are situated outside the conduit system, the external environmental conditions should be ascertained. Examples of these external conditions are a) atmospheric temperature and relative humidity ranges, b) likelihood of electrical interference, and c) likelihood of mechanical shock. ISO/TR
32、9824:2007(E) ISO 2007 All rights reserved 3 5 Selection of method 5.1 General In selecting the most appropriate method, the factors in 5.2 should be taken into account. 5.2 Factors 5.2.1 Frequency and duration of measurement The response of the conduit system to inputs of storm run-off may require m
33、easurements to be taken at frequent intervals to allow the hydrograph to be defined. The recording intervals may need to be one minute or less. The duration of flow measurement at a site should be consistent with the intended use of the data. 5.2.2 Physical conditions The physical conditions that ma
34、y affect the choice of method are a) ease of access to the site, b) dimensions of the conduit, c) upstream and downstream conduit integrity, d) junctions, bends, connections, bifurcations, inlets and outlets, e) bed load, silt load and suspended solids, f) range of depth and discharge, g) range of v
35、elocity, h) flow directions, i) atmosphere within the conduit, e.g. temperature, humidity and quality, j) the nature and concentration of dissolved, floating and suspended solids. The material/pollutant may be classified into four groups: 1) pollutants and sediments in solution; 2) finely suspended
36、sediments with median diameter = 0,062 mm; 3) coarse sediments where median diameter = 3,5 mm; 4) gross solids where particulate matter is greater than 6 mm in any two dimensions. 5.2.3 Site surveys It is desirable that a preliminary survey is made to decide on the suitability of the site taking due
37、 account of the various physical conditions as listed in 5.2.2. In addition, it may be necessary to abide by specific national or local health and safety regulations that could be in force for persons working in closed conduits or confined spaces. ISO/TR 9824:2007(E) 4 ISO 2007 All rights reserved6
38、Methods of measurement 6.1 Volumetric methods 6.1.1 Description In the volumetric method, the change in level of fluid in a reservoir is measured over time to deduce flow-rate, given a known relationship between fluid depth and volume. Account needs to be taken of any simultaneous inflows and outflo
39、ws that are occurring. For example, for a wet well system that is emptied by a pump turned on and off by high and low level switches, the inflow may be calculated from the time to fill, i.e. when the pumps are off. The discharge may also be calculated from the time to empty when the pumps are on, as
40、suming that the inflow is constant. This method may be applied where fluid depth is monitored by fixed point level switches or a continuous level sensor. Using this method, flow-rate is averaged over the time period to fill or empty the tank, hence short-term peaks or troughs in the instantaneous fl
41、ow-rate may not be captured. The use of continuous level measurement equipment to take intermediate readings may enable any variations in the flow-rate to be identified. 6.1.2 Attributes and limitations Fluid level can be measured by non-contact means minimizing maintenance requirements. This method
42、 requires a flow computer but otherwise no additional sensors need be installed, as those already in place to control the pump switching are used. The method can only be used where there is an appropriate tank, wet well or reservoir. The volume/depth relationship can be difficult to determine for ir
43、regularly shaped reservoirs or those with intrusions and internal structures. This method is usually not practical in an underground system. Sediment and sludge building up in the reservoir can change the volume/depth relationship. 6.1.3 Equipment The following will be needed to apply this method: a
44、) a suitable reservoir; b) a means of determining fluid level at two or more points in the reservoir; c) a suitably programmed flow computer. 6.1.4 Application This method may either be used for short-term flow surveys, calibration and verification of permanently installed equipment or as a permanen
45、t means of measurement. 6.1.5 Uncertainties The performance of this method is dependent on the certainty with which the volume/depth relationship of the reservoir is known, the resolution and accuracy of the equipment used to measure the fluid depth in the tank and the presence and character of the
46、inflows and outflows. The resolution of the level sensor(s) should be considered against the changes in depth which may be encountered using a reservoir with large surface area, ISO/TR 9824:2007(E) ISO 2007 All rights reserved 5 i.e. the volume change in a reservoir with a large cross-sectional area
47、 will change greater for a given change in fluid depth than one with a smaller cross-sectional area. Uncertainties (with a coverage factor of 2 and an approximate confidence level of 95 %) of less than 2 % are achievable for a clean reservoir having a precisely defined volume/depth relationship and
48、using a high resolution depth sensor with an uncertainty within 0,5 %. Generally with a good installation, the uncertainty will be of the order of 5 %. 6.2 Tracer and dilution method 6.2.1 Basic principles The basis of the tracer and dilution method is to inject a substance into the flow that can be
49、 easily distinguished from the bulk liquid and thereafter detect that substance at a point downstream. There are two distinct ways in which the method may be applied: a) transit time that measures the time taken for a sudden injection of tracer to travel from one point to another; b) dilution gauging which compares the concentration of the tracer injected into the bulk fluid with the concentration detected downstream of the injection point. This can be further subdivided into constant rate injection or tracer integration methods. The c
