Published on：2014-12-2 10:32:59 Hits：
Throttle flowmeter is a typical differential pressure flowmeter. Industrial production is used to measure gases, liquids and steam
The most commonly used gas flow A flow meter. According to the survey, the meter in steel mills, oil refineries and other industrial production systems are used around (70-80)% of throttle flowmeter. In the whole field of industrial production, throttle flow meter also accounted for more than half the total number of the instrument. Throttle flowmeter so get so widely used, mainly because it has the following two very distinct advantages:
① simple structure, easy to install, reliable, low cost, and with a certain accuracy. To meet the needs of engineering measurements.
② has a long history of use, rich, reliable experimental data, the design process has been standardized. As long as the standard orifice flowmeter design process, does not require the actual calibration can be performed in a known flow rate range of uncertainty
Especially the second advantage, making the throttle flow meter in the manufacture and use are very convenient. Because of a meter, especially large traffic flow measurement with juice, in the test will encounter various difficulties.
Throttle flowmeter usually consists of fluid flow can be converted into a differential pressure signal, a throttle device and measuring differential pressure and differential pressure flow meter display components. The throttling means is mounted in a flow conduit, also known as "one unit", comprising a throttle member and a pressure measuring device after the straight pipe section. The display device is also called a "second device", which includes differential signal line required to facilitate measurement of the instrument.
Many countries have done a lot for throttling device research. AGA (American Gas Association) and ASME (American Society of Mechanical Engineers) from the beginning of this century began to experiment with throttling device, the results were published in 1969 and 1971 reports. DIN (German Industrial Standard), and has long been prescribed for throttling device, to 1969 has been revised six times the international standard difficult Organization (ISO) summarizes the results of basic research in various countries on the 1967 respectively and 1968 published the ISO / R541 and ISO / R781, as the throttling device with international standards. 1980 again in front of the two documents were revised and published suitable for plates, nozzles and venturi tubes international standard ISO 5167. China is also published in 1981 a throttling device flow measurement national standard GB 2624, on the corner tapping, flange pressure of standard orifice plate and corner tapping standard nozzle made specific provisions.
When using standard throttling device, the fluid nature and status must meet the following conditions:
① fluid must be filled with pipes and throttling device, and continuously flowing through the pipe.
② fluid must be a Newtonian fluid, i.e., is physically and thermodynamically homogeneous, single-phase, or may be considered to be single phase, comprising mixing a gas, solution, and dispersion of the particles is less than o. 1 m colloid. There are not more than 2% (by mass component) uniformly dispersed solid particles, or liquid has not more than 5% (by volume component) uniformly dispersed gas bubbles, may also be considered a single-phase fluid in the gas. But its density should take the average density.
③ fluid flow through the orifice at the intersection does not occur.
④ fluid flow does not change or changes very slowly over time.
⑤ the fluid flowing through the orifice before the stream is non-parallel to the axis of the swirl duct.
Standard throttling device is not available for flow measurement of dynamic flow and critical flow.
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