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『Selection of orifice flowmeter』Related information(clamp on meter|electromagnetic meter|venturi meterrotameter|orifice meter|ultrasonic flow meter|mass flow meter|coriolis mass flow meter|coriolis flow meter|magnetic flow meter|magmeter flow meter|magflow flow meter|mag meter flow meter|electromagnetic flow meter|vortex flow meter|turbine flow meter|thermal mass flow meter|thermal flow meter|rotameter flow meter)
1. Selection of orifice flowmeter
1. Pipeline conditions:
(1) The straight pipe section before and after the throttling element must be straight and there must be no visible bending. (2) The straight pipe section used for installing throttling components should be smooth. If it is not smooth, the flow coefficient should be multiplied by the roughness correction factor.
(3) In order to ensure that the fluid flow forms a fully developed turbulent velocity distribution 1D in front of the throttling element, and to make this distribution uniformly axisymmetric, 1) the straight pipe section must be circular, and the roundness requirements for the 2D range in front of the throttling element are very strict, with certain roundness indicators. Specific measurement method: (A) Measure the inner diameters of at least four pipes on four vertical pipe sections, OD, D/2, D, and 2D, at equal angular distances, and take the average value D. The difference between any single inner diameter measurement value and the average value shall not exceed ± 0. 3% (B) After the throttle element, 8 single inner diameter measurements were taken at OD and 2D positions using the above method. The maximum deviation between any single measurement and D should not exceed ± 2%. 2) A sufficiently long straight pipe section is required before and after the throttle element, which is related to the form of the local resistance element in front of the throttle element and the diameter ratio β, as shown in Table 1 (β=d/D, where d is the diameter of the orifice plate opening and D is the inner diameter of the pipeline).
(4) The length of the straight pipe section between the first resistance piece and the second resistance
(5) When the upstream side of the throttling element is an open space or a large container with a diameter ≥ 2D, the length of the straight pipe between the open space or large container and the throttling element shall not be less than 30D (15D). If there are other local resistance elements between the throttling element and the open space or large container, in addition to the minimum straight pipe length 1 specified in Table 1 between the throttling element and the local resistance element, the total length of the straight pipe from the open space to the throttling element shall not be less than 30D (15D). Table 1 Minimum straight pipe length on the upstream and downstream sides of the throttling element. Local negative force element form and minimum straight pipe length L on the upstream side of the throttling element. Note:
1. The above table is only for standard throttling devices and can be used as a reference for special throttling devices.
2. The column number system is a multiple of the inner diameter D of the pipe.
3. The number outside the parentheses in the table represents the value of "zero additional relative limit error", and the number inside the parentheses represents the value of "± 0.5% additional relative limit error". When there is a value in parentheses in the length of the straight pipe section, the limit relative error of flow measurement is τ Q/Q. If the actual length of the straight pipe section is greater than the value in parentheses but less than the value outside the enclosed