GB/T 2624-1993 Flow measurement throttling devices - Measuring the flow of fluids filling a circular tube using orifice plates, nozzles and venturi tubes
Some standard content:
National Standard of the People's Republic of China
Flow measurement throttling device
Measurement of fluid flow by means of orifice plates, nozzles and Venturi tubes instrted in circulan cross-section conduits running full GB/T 2624..-93
Replaces GB2624-81
This standard is equivalent to the international standard IS0) 5167-1 (1991) "Measurement of flow by differential pressure device Part · Orifice plates, nozzles and Venturi tubes installed in circular cross-section conduits full of fluid". 1 Content and scope of application
This standard specifies the structural form and technical requirements of orifice plates, nozzles and Venturi tubes in throttling devices, as well as the use, installation and operating conditions, inspection rules and inspection methods of throttling covers. At the same time, the necessary information on the calculated flow rate and its related uncertainty is also given.
This standard applies to the following pressure taking methods: angle pressure taking, flange pressure taking, 1) and 1)/2 pressure taking, and throttling devices with orifice plates, nozzles and venturi tubes as throttling devices. Each throttling device can only be used within the specified limit. The throttling devices specified in this standard are subject to the following conditions: the fluid must fill the circular tube and the throttling device; the flow of the fluid through the measuring section must remain subsonic, stable or only change slowly with time; the fluid must be a single-phase fluid or can be considered as a single-phase fluid. This standard does not apply to pipes with a nominal diameter less than 50mm and a nominal diameter greater than 1200mm, or pipe Reynolds number less than 3150.
2 Reference standards
ZBN10002 Flow measurement and instrumentation terms
7BY002 Basic environmental conditions and test methods for transportation and storage of instruments and meters ZBY003 General technical conditions for instrument packaging 3 Codes and terms
3.1 Codes
The codes used in this standard are shown in Table 1.
Table 1 Symbol
Flow coefficient
The throttle hole or throat diameter of the throttle under working conditions State Technical Supervision Bureau 1993-02-03 Approved quantity
Dimensionless
Implementation on 1993-08-01
GB/T 2624—93
Continued Table 1
Relative uncertainty of the inner diameter of the upstream pipe under working conditions (inner diameter of the upstream pipe of the classic Venturi tube)
Asymptotic velocity coefficient
Equivalent absolute roughness (see 7.3.1)
Pressure tapping distance
Relative pressure tapping distance, L—1/D
Absolute static pressure of the fluid
Mass flow rate
Volume flow rate
Arc radius
Roughness height parameter
Reynolds number
Reynolds number related to D
Reynolds number related to d Related Reynolds number
Fluid temperature
Average axial velocity of the fluid in the pipe
Diameter ratio, β-d/D
Specific heat ratio
Pressure loss
Expansion coefficient
Equal entropy index
Dynamic viscosity of the fluid
Kinematic viscosity of the fluid, —p
Relative pressure loss
Density of the fluid
Pressure ratio, t=P2/P
Diffusion angle
Dimensionless
Dimensionless
Especially dimensionless
ML'T 2
dimensionless
dimensionless
dimensionless
especially dimensionless
dimensionless
ML\IT-2
dimensionless
dimensionless
MI-T-1
dimensionless
dimensionless
dimensionless
Note: () The code M in the dimension stands for mass, the code L stands for length, the code T stands for time, and the code θ stands for temperature. ) Subscript 1 represents the parameters on the plane of the upstream pressure tapping port, and subscript 2 represents the parameters on the plane of the downstream pressure tapping port. 3.2 Terminology
GB/T 2624--93
In addition to the relevant terms in ZBN10002, this standard also specifies the following terms; 3.2.1 Throttling device A set of devices that cause the fluid flowing in the pipeline to produce a static pressure difference. The whole set of throttling devices consists of a throttling device, a pressure taking device, and a front and rear straight pipe section that meets the requirements.
Synonym, differential pressure device differentialpressuredevice 3.2.2 Throttling element Throttling element An element in the throttling device that causes fluid contraction and produces differential pressure on its upstream and downstream sides. The throttling elements included in this standard include orifice plates, nozzles, and Venturi single tubes.
3.2.3 Standard throttling element standardthrottlingelement Within the use limit specified in this standard, the throttling element that can be designed, manufactured, installed and used according to the data and requirements provided in this standard is a standard throttling element. That is, standard orifice plate, standard nozzle, standard venturi tube (hereinafter referred to as orifice plate, nozzle, venturi tube), etc. 3.2.4 Orifice
The opening with the smallest cross-sectional area in the throttling part. The throttling hole of the standard throttling part is round and concentric with the throttling part. Synonym: throat
3.2.5 Orifice plate
The orifice plate is a thin plate with circular perforations obtained by machining. Its cylindrical surface of throttling hole is perpendicular to the upstream end face of the orifice plate, its edge is sharp, and the thickness of the orifice plate is relatively small compared with the diameter of the orifice plate. 3.2.6 Nozzle
The throttling part whose axial section is composed of a circular arc-shaped contraction part and a cylindrical throat. 3.2.7 Venturi tube
The throttling part whose axial section is composed of an entry contraction part, a cylindrical throat and a conical diffusion section. 3.2.8 diameter ratio
The ratio of the diameter of the orifice (or throat) of a throttling device to the inside diameter of the measuring pipe upstream of the throttling device. When the inside diameter of the cylindrical section at the inlet of the throttling device is equal to the inside diameter of the pipe (such as the classic Venturi tube), the diameter ratio is the ratio of the throat diameter to the inside diameter of the cylindrical section at the upstream pressure tapping plane. 3.2.9 wall pressure tapping A hole drilled in the pipe wall, the inner edge of which is flush with the inner surface of the pipe. The wall pressure tapping is usually a circular hole, but it can also be an annular gap. 3.2.10 differential pressure The difference in static pressure measured at the wall pressure tapping, one at the pressure tapping upstream of the throttling device and the other at the pressure tapping downstream of the throttling device, when any height difference between the upstream and downstream pressure tappings has been taken into account. The term "differential pressure" applies only to the difference in static pressures obtained at the pressure tapping locations specified in this standard. 3.2.11 Pressure ratio pressure ratio
The ratio of the absolute static pressure at the downstream pipe wall pressure tapping port to the absolute static pressure at the upstream pipe wall pressure tapping port. 3.2.12 Reynolds number Reynolds number
A dimensionless parameter that characterizes the ratio of the inertial force to the viscous force of a fluid. The Reynolds number used in this standard can be the Reynolds number expressed by the upstream condition parameters of the fluid and the upstream pipe diameter, as shown in formula (1). It can also be the Reynolds number expressed by the upstream condition parameters of the fluid and the orifice diameter or throat diameter of the throttling device, as shown in formula (2). Rep
3.2.13 Isentropic exponent GB/T 2624-.93
The ratio of the relative change in pressure to the relative change in density under reversible adiabatic (isotropic) conversion conditions. It changes with the properties of the gas and with changes in its temperature and pressure.
There are many gases and vapors whose isobaric indices have not been published so far. In order to calculate the flow rate, these gases can be regarded as ideal gases in this standard and the isobaric indices can be replaced by the specific heat ratio. 3.2.14 discharge coefficient For incompressible fluids, the discharge coefficient C is the ratio of the actual flow value through the throttling device to the theoretical flow value. It is a dimensionless pure number and can be determined using formula (3).
C = _4qm V-
d2 V2 × p
For a given throttling device under certain installation conditions, this value is only related to the Reynolds number. For different throttling devices, provided that these devices are geometrically similar and under the same Reynolds number, the value of is the same. This standard is based on experimentally determined data and provides an equation for calculating the discharge coefficient C. The relationship between the outflow coefficient C and the flow coefficient is:
C=α/E
Where: E is the asymptotic velocity coefficient and is determined by the following formula: E
So the flow coefficient α can be determined by the following formula: i
α=CXEwwW.bzxz.Net
3.2.15 Expansibility factor
Taking into account the compressibility of the fluid, when a given throttling device is calibrated with a compressible fluid (gas), the ε,C value can be obtained by formula (4), which depends on the Reynolds number, the differential pressure value and the gas isentropic index value. Wherein the outflow coefficient C is the value determined by direct calibration in the liquid at the same Reynolds number. Therefore, the expansibility coefficient is a coefficient determined by formula (5). 49m V1= p4
rda 24P × p
Cnd2 2P × pi
When the fluid is incompressible, E, is equal to 1; when the fluid is compressible, E, is less than 1.18
（４）
GB/T2624-93
Experiments show that E, has nothing to do with the Reynolds number. For a given throttling device with a known diameter ratio, E, depends only on the differential pressure, static pressure, etc. The value of ε, given in this standard for the orifice plate is determined by experimental methods. The values of ε, given in this standard for the nozzle and the venturi tube are calculated using the general energy equation for thermodynamics.
3.2.16 Roughness criterion Roughness height parameter R. is the arithmetic mean deviation from the average line of the measured profile. The so-called average line is a line whose sum of the squares of the distances from the effective surface is the smallest. For machined surfaces, R. can be measured with standard equipment. Many pipelines use relative roughness. The equivalent absolute roughness K can be determined by experiment. Appendix F (reference) lists the K values of different pipeline materials.
4 Measurement principle and calculation method
4.1 Measurement principle
The fluid filling the pipeline flows through the throttling device in the pipeline. The flow beam will form a local contraction at the throttling device, thereby increasing the flow rate and reducing the static pressure. Therefore, a static pressure difference (or differential pressure) is generated before and after the throttling device. The higher the flow rate of the fluid, the greater the differential pressure of dust before and after the throttling device. Therefore, the flow rate of the fluid when it flows through the throttling device can be measured by measuring the differential pressure. This measurement method is based on the law of conservation of energy and the flow continuity equation.
Assuming that the uncalibrated throttling device is geometrically and dynamically similar to the throttling device that has been fully experimentally calibrated, that is, it meets the requirements of this standard, the relationship between mass flow and differential pressure is determined by formula (6) or formula (7) within the uncertainty specified in this standard. The relationship between volume flow and differential pressure is determined by formula (9). Ym
4.2 Calculation method of throttling device diameter ratio
2 V2AP × P1
\d2 2AP X pz
2 = e × V1 +AP/P2
（6）
（9）)
When determining the diameter ratio of the throttling device installed in the pipeline, C and =1 or E2 in the basic formula (6) or (7) are generally unknown. Therefore, the type of throttling device used, the flow rate and the corresponding differential pressure value should be determined first. Then the relevant 9㎡ and △P values are introduced into formula (10), and finally the throttling diameter ratio is determined by iteration method, which can be referred to Appendix E (reference). Cep2
Y1- β4
(10）
where and ε can be substituted into the upstream fluid density and expansion coefficient, or into the downstream fluid density and expansion coefficient, respectively. 19
4.3 Calculation of flow rate
GB/T2624--93
Substitute the known quantities into formula (6) or formula (7) to obtain the flow rate. For convenience, Tables A1 to A16 in Appendix A (Supplement) give the C value and ε value respectively. The C value is a function of β, Ren and D. The values in the table are not for accurate interpolation, nor are they allowed to be extrapolated. 4.3.1 Except for the Venturi tube. The C value is related to Ren, which itself is related to Qm. In this case, the final value of C (final value of Qm) must be obtained by iteration. For the iteration procedure, initial value estimation and assumptions, see Appendix E (reference). 4.3.2 AP is the differential pressure defined in 3.2.10. 4.3.3 The d and D in the formula are the diameter values under operating conditions. The values measured under any other conditions must be corrected for the values of d and D according to the temperature and pressure values of the fluid at the time of measurement. 4.3.4 The density and viscosity of the fluid under operating conditions must be known when calculating the flow rate. 4.4 Determination of density
The density at the plane of the upstream or downstream pressure tapping can be measured directly, or it can be calculated based on the data of the static pressure, temperature and other characteristics at the corresponding plane.
4.4.1 The static pressure of the fluid should be measured at the plane of the upstream or downstream pressure tapping. 4.4.1.1: In general, the static pressure tapping is separated from the upstream or downstream pressure tapping used to measure the differential pressure. Unless it is necessary to measure the upstream or downstream pressure separately, it is allowed to connect a static pressure tapping to the upstream or downstream pressure tapping for measuring the differential pressure, but it must be ensured that this double connection does not cause any error in the differential pressure measurement. 4.4.1.2 The static pressure value used in the calculation of this standard should be the value on the horizontal plane at the center of the measuring cross section, which may be different from the pressure value measured at the pipe wall.
4.4.2 The fluid temperature is preferably measured downstream of the throttling device, and the thermometer socket or sleeve should occupy as little space as possible. If the thermometer socket or sleeve is located downstream, the distance between it and the throttling device should be equal to or greater than 5L (when the fluid is a gas, it shall not exceed 15D)); if the thermometer socket or sleeve is located upstream, the distance between it and the throttling device should meet the requirements of Table 2. If the fluid is a gas, its upstream temperature can be calculated from the temperature measured downstream. Within the scope of application of this standard, it can be assumed that the upstream and downstream temperatures of the fluid are the same. 4.4.3 Any method of determining the density, static pressure, temperature and viscosity of the fluid is acceptable provided that the velocity distribution at the measurement cross section is not disturbed in any way.
4.4.4 The temperature of the throttling element and the temperature of the fluid upstream of the throttling element may be considered to be the same (see 6.1.10). 5 General requirements for measurement
5.1 Throttling devices
5.1.1 Throttling devices shall be manufactured, installed and used in accordance with the provisions of this standard. When the manufacturing and use conditions of the throttling device exceed the limits specified in this standard, the throttling device must be calibrated separately. 5.1.2 The throttling device shall be checked regularly to ensure that it is consistent with this standard. It should be noted that even apparently neutral fluids may form deposits and deposits on the throttling element, which may cause fluctuations or changes in the flow coefficient over a period of time, which may cause its value to exceed the uncertainty range given in this standard. 5.1.3 The throttling device shall be made of materials with known expansion coefficients, unless the user confirms that the dimensional changes caused by temperature changes are negligible.
5.2 Types of fluids
5.2.1 Fluids can be compressible gases or incompressible liquids (including fluids that can be considered incompressible). 5.2.2 Fluids must be Newtonian fluids and must be uniform, single-phase fluids in physics and thermodynamics. Or they can be considered single-phase fluids. Colloidal solutions with a high degree of dispersion (such as milk) can be considered equivalent to single-phase fluids. 5.2.3 For flow measurement, the density and viscosity of the fluid under working conditions must be known. 5.3 Flow state
5.3.1 The flow rate in the pipeline should not change with time, or actually only change slightly and slowly with time. This standard is not applicable to the measurement of pulsating flow.
GB/T2624--93
5.3.2 The uncertainty specified in this standard is valid only when the fluid does not undergo phase change when passing through the throttling device. The opening of the throttling device or the increase of the throat reduces the differential pressure, which can eliminate the phase change. When calculating the flow rate, the liquid is calculated according to the isothermal change and the gas is calculated according to the adiabatic change.
5.3.3 If the fluid is a gas, the pressure ratio should be equal to or greater than 0.75.6 Installation requirements
6.1 General
6.1.1 The flow measurement method specified in this standard is applicable to measuring fluids in circular cross-section pipes. 6.1.2 The fluid should fill the measuring pipe.
6.1.3 The throttling device should be installed immediately upstream of the throttling device at a position where the flow state of the fluid in the pipe is close to the typical fully developed turbulent flow state and there is no vortex (see 6.4). As long as the installation meets the requirements given in Chapter 6, the above requirements are considered to be met. 6.1.4 The throttling device should be installed between two cylindrical straight pipe sections with constant cross-sectional area, without any obstacles or connecting branches other than those specified in this standard (regardless of whether there is fluid flowing into or out of such branches). The pipe can be considered to be straight if it is shown to be straight by visual inspection. The shortest straight pipe section length that meets the above requirements varies with the type of flow blocker, the type of throttling device and the diameter ratio. The shortest straight pipe section length is shown in Tables 2 and 3. Table 2 Minimum straight pipe length required for orifice plates, nozzles and venturi nozzles Type of flow control device upstream of throttling device and minimum straight pipe length True diameter ratio
Single 90° elbow
Head or tee
(fluid flows out from only
branches
)
22(11)
28(14)
36(18)||tt ||46(23)
Two
or more
90°elbows
20(10)
22(11)
26(13)
32(16)
36(18)
42(21)
50(25)||tt ||Two
or more
90°elbows
34(17)
34(17)
34(17)
36(18)
36(18)
38(19)
40(20)
44(22)||tt ||48(24)
54(27)
62(31)
70(35)
80(40)
Reducer (changes from 2D
to D within the length
1.5n to
3D)
22(11)
30(15)||tt| |Gradually expanding pipe (within the length from
i to 2D
|[the ball valve is fully opened
changes to)
20(10)
22(11)
25(13)
30(15)
38(19)
54(27)
20(10
20(10)
22(11)
24(12)
26(13)
28(14)
32(16)||t t||36(18)
44(22)
full hole ball valve
or full gate valve
20(10)
24(12)||tt ||30(15)
The shortest straight pipe length downstream of the throttling device
(including all the throttling devices in this table)
For all diameter ratios β
GB/T2624---93
Continued Table 2
Throttling devices
Symmetrical reducers with a diameter ratio greater than or equal to 0.5, thermometer sleeves and sockets with a diameter less than or equal to 0.03D and a diameter between 0.03D and 0.13D [Measured shortest straight pipe length
20(10)
Note: The values in the table are the shortest straight pipe lengths required between the various throttling devices and the throttling device located upstream or downstream of the throttling device. ② The value without brackets is the value of "zero additional uncertainty" (see 6.2.3). The value with brackets is the value of "0.5% additional uncertainty" (see 6.2.4). () The length of the straight pipe section is expressed as a multiple of the diameter D). It should be from the upstream end of the throttling device. Table 3 The shortest straight pipe section required for the classic Venturi tube is in the plane!
Diameter ratio
Single 90° short half diameter elbow
Two or more
90° elbows
2. 5(1.5)
3. 5(2.5)
Two or more
90° elbows
In the range of 3.5 length
Mountain 3)
In the range of length
Change from a tapered converging to a tapered diverging in 1)
10. 5(2.5)
11.5(3.5)
Umbrella-lift ball valve into a gate
Note: (1) The values listed in the table are the shortest straight pipe lengths required between the various flow-blocking parts upstream of the classic venturi tube and the classic venturi tube. ② The values without brackets are the values of "zero additional uncertainty" (see 6.2.3). 3 The values in brackets are the values of "0.5% additional uncertainty" (see 6.2.4).) The straight pipe sections are expressed as multiples of the diameter D. Measured from the plane of the upstream pressure tapping of the classic Venturi tube. At least within the length range shown in Table 3, the pipeline roughness should not exceed the roughness of the smooth pipe available on the market (about K/I) ≤ 10). (() Downstream straight pipe section: Pipe fittings or other flow-blocking parts located at least 4 times the throat diameter downstream of the throat pressure tapping plane (see Table 3) do not affect the measurement uncertainty.
③ The shortest straight pipe section length required by the classic Venturi tube is shorter than the straight pipe section length specified by the orifice plate, nozzle, and Venturi nozzle in Table 2. The original reason is:
a, they are obtained from different experimental results and different upstream connection conditions. h. Designing the contraction part of the classic Venturi tube can obtain a more uniform velocity distribution in its throat. Experiments show that for the same Diameter ratio, the shortest straight pipe section upstream of the classic Venturi tube is comparable to the orifice plate, nozzle and Venturi nozzle required to be short (7) The bending radius of the elbow should be equal to or greater than the pipe diameter. 1) The influence of these pipe fittings or flow control parts on the flow velocity in the pipe may appear after 40D, so this table cannot give values without brackets. 2) Since there is no pipe fitting or flow control part that is less than 0.5D away from the axis of the upstream pressure tapping of the Venturi tube, this table does not give values with brackets. 6.1.5 The pipe diameter D value used to calculate the throttling device diameter ratio should be the average value of the inner diameter within the upstream 0.5D length range of the upstream pressure tapping. The average inner diameter should be the average value of the inner diameter measured in at least three cross sections perpendicular to the axis, and the three cross sections are distributed within a 0.5D length range, of which two cross sections are 0D and 0.5D away from the upstream pressure tapping respectively, and in the case of a welded neck structure, 22
GB/T 262493
One cross section must be in the welding plane. If there is a clamping ring (see Figure 8a), the 0.5D value is measured from the upstream edge of the clamping ring. In each cross section, at least four diameters are measured and their arithmetic mean is calculated, and the four diameters are approximately equal angles apart. 6.1.6 The cross section of the pipe should be circular within the required minimum straight pipe section length. As long as the visual inspection shows that it is circular, the cross section is considered to be circular. Except for the area directly adjacent to the throttling device, special inspection should be carried out according to the type of throttling device used. In general, the roundness of the outside of the pipe can be used as the standard (see 6.5.1 and 6.6.1). The straight pipe section can be longitudinal Welded pipe, but the internal weld should be parallel to the axis of the pipe and meet the special requirements of the throttling device used for the pipeline. The angle between the pipe axis plane where the weld is located and the pipe axis plane where the axis of any pressure tapping is located should be greater than 30°. 6.1.7 The inner diameter D value of the measuring pipe should comply with the value specified for the measuring pipe by the throttling device used. 6.1.8 The inner surface of the pipe should be clean and meet the requirements of the roughness height parameter within a length range of at least 10I) upstream of the throttling device and at least 4D downstream.
6.1.9 Drain holes and vent holes
Drain holes and (or) vent holes can be set on the pipeline to discharge solid sediments and fluids other than the measured fluid. However, during flow measurement, the fluid shall not pass through the drain holes and vent holes. - In general, drain holes and vent holes are preferably not located near throttling devices. Exceptions can be made unless they cannot be avoided. The diameter of the drain hole or steam release hole should be less than 0.08D, and the straight-line distance between any of these holes and the axis of the pressure tapping on the same side of the throttling device must be greater than 0.5D. In addition, the angle between the pipe axis plane where the axis of the drain hole or vent hole is located and the pipe axis plane where the axis of any pressure port is located should be greater than 30°
6.1.10 Pipes and pipe flanges should be equipped with insulation sleeves. If the fluid temperature change between the upstream shortest straight pipe section inlet and the downstream shortest straight pipe section outlet meets the flow measurement uncertainty requirements, the pipes need to be equipped with insulation sleeves. 6.2 The shortest upstream and downstream straight pipe sections to be installed between various flow-blocking and throttling components 6.2.1 The values in Tables 2 and 3 are the specified shortest straight pipe section lengths. 6.2.2 The straight pipe section lengths specified in Tables 2 and 3 are the minimum values. In actual applications, it is recommended to use a pipe section longer than the specified length. In research work, in order not to introduce additional uncertainty, the recommended straight pipe section length is at least twice the value specified in Tables 2 and 3 for "zero additional uncertainty".
6.2.3 When the straight pipe length is equal to or greater than the value for "zero additional uncertainty" in Tables 2 and 3, it is not necessary to add any additional uncertainty to the uncertainty of the outflow coefficient. 6.2.4 When the upstream or downstream straight pipe length is less than the value of "zero additional uncertainty" and equal to or greater than the value of "0.5% additional uncertainty", as shown in Tables 2 and 3, an additional uncertainty of ±0.5% should be arithmetically added to the uncertainty of the outflow coefficient. 6.2.5 When the upstream or downstream straight pipe length is less than the value of "0.5% additional uncertainty" given in Table 2 or Table 3, and when the upstream and downstream straight pipe lengths are simultaneously less than the value of "zero additional uncertainty", this standard does not give additional uncertainty values. 6.2.6 The valves listed in Tables 2 and 3 should be fully open. The valve for regulating flow should be located downstream of the throttling device. The shut-off valve upstream of Ding should preferably be a "gate valve" type and should be fully open. 6.2.7 After a single change of flow direction (elbow or tee), if a pressure tapping port is drilled separately, the axis of the pressure tapping port should be perpendicular to the plane of the elbow or tee.
6.2.8 The values given in Tables 2 and 3 were obtained by testing with a long straight pipe section installed upstream of the specific pipe fitting in question, so it can be It is assumed that the flow upstream of the throttling device is a fully developed and vortex-free flow. Since such conditions are difficult to achieve in practice, the following precautions can be used as a guide for formal installation: If the throttling device is installed in the pipeline after the open space or large container, whether it is directly led out or through any pipe fittings, the total length of the pipeline between the open space and the throttling device should not be less than 30D (in the absence of experimental data, the classic Venturi single arm can adopt the straight pipe section conditions required by the orifice plate and nozzle). If there are any pipe fittings or throttling parts installed between the throttling device and the knocked-open space or large container, the straight pipe section lengths given in Tables 2 and 3 are also applicable to the straight pipe section lengths between this pipe fitting or the positive flow fitting and the throttling device. b When several pipe fittings other than 90° elbows are connected in series upstream of the throttling device, the following should be implemented. Description and rules: There should be a straight pipe section between the pipe fitting (1) closest to the throttling device and the throttling device, and its length shall be the value listed in Table 2 or Table 3 according to the type of pipe fitting (1) and the actual 323
GB/T2624--93
value. In addition, there should be a straight pipe section between the pipe fitting (1) and the pipe fitting (2) in front of the pipe fitting (1), and its length shall be half of the value listed in Table 2 or Table 3 (the type of pipe fitting (2) is β==07 regardless of the actual value of 3). When the pipe fitting (2) is a symmetrical reduction pipe fitting, this situation shall be handled in accordance with the above item. Note: In the case of several 90° elbows, regardless of the length between two consecutive elbows, the values listed in Table 2 or Table 3 can be used as a reference. If the shortest straight pipe section used is the value in brackets , an additional uncertainty of ±0.5% should be added to the uncertainty of the outflow coefficient.
6.3 Flow Conditioners
If the throttle is installed downstream of any flow restriction other than those listed in Table 2 or Table 3, it is recommended to use a flow conditioner of the type described in Figures 1 to 5 in Section 6.3.2. In addition, when a throttle with a larger diameter than 8 is used, a flow conditioner can also be installed on the pipeline. In this way, it is sometimes allowed to use a straight pipe section smaller than the values listed in Table 2 or Table 3. If the flow conditioner is installed in accordance with the requirements of Section 6.3.1, it will not introduce any additional uncertainty to the uncertainty of the outflow coefficient. 6.3.1 Installation
Any type of flow conditioner used should be installed in the straight pipe section between the throttle and the flow restriction or pipe fitting closest to the upstream of the throttle. The straight pipe length between the flow regulator or pipe and the regulator should be at least 20LD (the length is measured from the upstream end of the flow regulator), and the straight pipe length between the flow regulator and the throttling device should be at least 221) (the length is measured from the downstream end of the flow regulator). Exceptions can be made unless the provisions of 6.1.3 are met. The flow regulator is fully effective only when there is a minimum gap around the throttling tube of the flow regulator so that there is no bypass flow that can hinder its normal function. When a flow regulator that meets the requirements of this standard is used in combination with the above-mentioned specified pipeline length, the throttling device can be installed on a pipeline with any velocity distribution surface for flow measurement. 6.3.2 Five standard types of flow regulators are shown in Figures 1 to 5. The type of flow regulator is selected according to the fluid velocity distribution in the pipeline upstream of the throttling device and the pressure loss allowed by the flow measurement system. The pressure loss values generated by five types of flow conditioners are given below (the values are approximate): Type A: 5pU/2;
Type B (with inlet chamfer): 11αU\/2; Type B (without inlet chamfer): 140U2/2;
Type C: 5uU/2;
Type D: 0.250U2/2;
Type E: 0.250U2/2
For Type A, Type B and Type C, the pressure loss varies with the ratio of the total through-hole area to the pipe flow area. 21
6810=a/p
T/ R= 0 75
GB/T 2624
r /R =0. 0
9-0-#/4
98-0-17
d/D 0 13865
T/R= 0. 25
Flow direction
Porous lower pole
GB/T2624
Note: In order to reduce pressure loss, the entrance of the hole can be made into a 45\ chamfer. 93
Figure 2B type: porous plate flow conditioner
A-A section
Figure 3C type: tube bundle flow conditioner
d≤0.05b8 The values given in Tables 2 and 3 were obtained by testing with a long straight pipe section installed upstream of the specific pipe fitting in question, so it can be assumed that the flow upstream of the choke is a fully developed and vortex-free flow. Since such conditions are difficult to achieve in practice, the following notes can be used as a guide for formal installation: If the throttling device is installed in the pipeline after the open space or large container, whether it is directly led out or through any pipe fittings, the total length of the pipeline between the open space and the throttling device should not be less than 30D (in the absence of experimental data, the classic Venturi single arm can adopt the straight pipe section conditions required by the orifice plate and nozzle). If any pipe fittings or chokes are installed between the throttling device and the knocked-open space or large container, the straight pipe section lengths given in Tables 2 and 3 also apply to the straight pipe section lengths between this pipe fitting or yang flow device and the throttling device. b. When several pipe fittings other than 90° elbows are connected in series upstream of the throttling device, the following layout rules should be implemented: There should be a straight pipe section between the pipe fitting (1) closest to the throttling device and the throttling device, and its length should be the value listed in Table 2 or Table 3 according to the type of pipe fitting (1) and the actual 323
GB/T2624--93
value. In addition, there should be a straight pipe section between the pipe fitting (1) and the pipe fitting (2) in front of the pipe fitting (1), and its length should be half of the value listed in Table 2 or Table 3 (the type of pipe fitting (2) is β==07 regardless of the actual value of 3). When the pipe fitting (2) is a symmetrical contraction pipe fitting, this situation should be handled in accordance with the above item. Note: In the case of several 90° elbows, regardless of the length between two consecutive elbows, the values listed in Table 2 or Table 3 can be used as a reference. If the shortest straight pipe section used is one of the values in brackets, an additional uncertainty of ±0.5% should be added to the uncertainty of the outflow coefficient.
6.3 Flow Conditioners
If the throttle is installed downstream of any flow restriction other than those listed in Table 2 or Table 3, it is recommended to use a flow conditioner of the type described in Figures 1 to 5 in 6.3.2. In addition, when a throttle with a larger diameter than 8 is used, a flow conditioner can also be installed on the pipeline, which sometimes allows the use of a straight pipe section smaller than the values listed in Table 2 or Table 3. If the flow conditioner is installed in accordance with the requirements of 6.3.1, it will not introduce any additional uncertainty to the uncertainty of the outflow coefficient. 6.3.1 Installation
Any type of flow conditioner used should be installed in the straight pipe section between the throttle and the flow restriction or pipe fitting closest to the upstream of the throttle. The straight pipe length between the flow regulator or pipe and the regulator should be at least 20LD (the length is measured from the upstream end of the flow regulator), and the straight pipe length between the flow regulator and the throttling device should be at least 221) (the length is measured from the downstream end of the flow regulator). Exceptions can be made unless the provisions of 6.1.3 are met. The flow regulator is fully effective only when there is a minimum gap around the throttling tube of the flow regulator so that there is no bypass flow that can hinder its normal function. When a flow regulator that meets the requirements of this standard is used in combination with the above-mentioned specified pipeline length, the throttling device can be installed on a pipeline with any velocity distribution surface for flow measurement. 6.3.2 Five standard types of flow regulators are shown in Figures 1 to 5. The type of flow regulator is selected according to the fluid velocity distribution in the pipeline upstream of the throttling device and the pressure loss allowed by the flow measurement system. The pressure loss values generated by five types of flow conditioners are given below (the values are approximate): Type A: 5pU/2;
Type B (with inlet chamfer): 11αU\/2; Type B (without inlet chamfer): 140U2/2;
Type C: 5uU/2;
Type D: 0.250U2/2;
Type E: 0.250U2/2
For Type A, Type B and Type C, the pressure loss varies with the ratio of the total through-hole area to the pipe flow area. 21
6810=a/p
T/ R= 0 75
GB/T 2624
r /R =0. 0
9-0-#/4
98-0-17
d/D 0 13865
T/R= 0. 25
Flow direction
Porous lower pole
GB/T2624
Note: In order to reduce pressure loss, the entrance of the hole can be made into a 45\ chamfer. 93
Figure 2B type: porous plate flow conditioner
A-A section
Figure 3C type: tube bundle flow conditioner
d≤0.05b8 The values given in Tables 2 and 3 were obtained by testing with a long straight pipe section installed upstream of the specific pipe fitting in question, so it can be assumed that the flow upstream of the choke is a fully developed and vortex-free flow. Since such conditions are difficult to achieve in practice, the following notes can be used as a guide for formal installation: If the throttling device is installed in the pipeline after the open space or large container, whether it is directly led out or through any pipe fittings, the total length of the pipeline between the open space and the throttling device should not be less than 30D (in the absence of experimental data, the classic Venturi single arm can adopt the straight pipe section conditions required by the orifice plate and nozzle). If any pipe fittings or chokes are installed between the throttling device and the knocked-open space or large container, the straight pipe section lengths given in Tables 2 and 3 also apply to the straight pipe section lengths between this pipe fitting or yang flow device and the throttling device. b. When several pipe fittings other than 90° elbows are connected in series upstream of the throttling device, the following layout rules should be implemented: There should be a straight pipe section between the pipe fitting (1) closest to the throttling device and the throttling device, and its length should be the value listed in Table 2 or Table 3 according to the type of pipe fitting (1) and the actual 323
GB/T2624--93
value. In addition, there should be a straight pipe section between the pipe fitting (1) and the pipe fitting (2) in front of the pipe fitting (1), and its length should be half of the value listed in Table 2 or Table 3 (the type of pipe fitting (2) is β==07 regardless of the actual value of 3). When the pipe fitting (2) is a symmetrical contraction pipe fitting, this situation should be handled in accordance with the above item. Note: In the case of several 90° elbows, regardless of the length between two consecutive elbows, the values listed in Table 2 or Table 3 can be used as a reference. If the shortest straight pipe section used is one of the values in brackets, an additional uncertainty of ±0.5% should be added to the uncertainty of the outflow coefficient.
6.3 Flow Conditioners
If the throttle is installed downstream of any flow restriction other than those listed in Table 2 or Table 3, it is recommended to use a flow conditioner of the type described in Figures 1 to 5 in 6.3.2. In addition, when a throttle with a larger diameter than 8 is used, a flow conditioner can also be installed on the pipeline, which sometimes allows the use of a straight pipe section smaller than the values listed in Table 2 or Table 3. If the flow conditioner is installed in accordance with the requirements of 6.3.1, it will not introduce any additional uncertainty to the uncertainty of the outflow coefficient. 6.3.1 Installation
Any type of flow conditioner used should be installed in the straight pipe section between the throttle and the flow restriction or pipe fitting closest to the upstream of the throttle. The straight pipe length between the flow regulator or pipe and the regulator should be at least 20LD (the length is measured from the upstream end of the flow regulator), and the straight pipe length between the flow regulator and the throttling device should be at least 221) (the length is measured from the downstream end of the flow regulator). Exceptions can be made unless the provisions of 6.1.3 are met. The flow regulator is fully effective only when there is a minimum gap around the throttling tube of the flow regulator so that there is no bypass flow that can hinder its normal function. When a flow regulator that meets the requirements of this standard is used in combination with the above-mentioned specified pipeline length, the throttling device can be installed on a pipeline with any velocity distribution surface for flow measurement. 6.3.2 Five standard types of flow regulators are shown in Figures 1 to 5. The type of flow regulator is selected according to the fluid velocity distribution in the pipeline upstream of the throttling device and the pressure loss allowed by the flow measurement system. The pressure loss values generated by five types of flow conditioners are given below (the values are approximate): Type A: 5pU/2;
Type B (with inlet chamfer): 11αU\/2; Type B (without inlet chamfer): 140U2/2;
Type C: 5uU/2;
Type D: 0.250U2/2;
Type E: 0.250U2/2
For Type A, Type B and Type C, the pressure loss varies with the ratio of the total through-hole area to the pipe flow area. 21
6810=a/p
T/ R= 0 75
GB/T 2624
r /R =0. 0
9-0-#/4
98-0-17
d/D 0 13865
T/R= 0. 25
Flow direction
Porous lower pole
GB/T2624
Note: In order to reduce pressure loss, the entrance of the hole can be made into a 45\ chamfer. 93
Figure 2B type: porous plate flow conditioner
A-A section
Figure 3C type: tube bundle flow conditioner
d≤0.05b
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