Sensor Limit Switch,Limit Switch Box,Series Limit Switch Haoxia Trading Co., Ltd. , http://www.jiasongvalve.com
From the perspective of the development of flow meters, the orifice flow has a wide range of applications: However, there are still some deficiencies in using standard orifice flowmeters to measure fluid flow. Over the years, people have been trying to find a reliable and accurate flowmeter for flow measurement. It is found that the vortex flowmeter has a simple structure and is easy to install and maintain. Compared with the orifice plate, there is no need for a pressure guiding tube and three sets of valves to reduce leakage, blockage and freezing. And other phenomena), the pressure loss is small (about 1/4-1/2 of the orifice flowmeter), the range is wide, the range ratio is up to 20BI (3BI for orifice plate), and the measurement accuracy is higher than the orifice flowmeter. In addition, vortex flowmeters also have a long service life, stable performance, a wide range of applicable fluids (liquids, gases, and vapors can be measured). Meter coefficients are not affected by the temperature, pressure, and viscosity of fluids within a specified Reynolds number range. And the influence of changes in composition and other characteristics have become more and more popular.
1 Working principle Vortex flowmeter is a new type of flow measuring instrument based on the principle of fluid oscillation. The measurement principle is shown in Fig. 1. When a non-linear column (vortex generator) with a vertical flow direction is inserted into the fluid, two rows of inner swirling columns are alternately generated on the downstream side. Vortex column."
In a certain Reynolds number range, the frequency f of the vortex release is related to the average velocity v of the fluid flowing through the vortex generator and the characteristic width d of the vortex generator. The following formula can be used:
f=StV/d(1)
In the formula,
f))) The frequency of release of the vortex;
v") the average velocity of the fluid flowing through the vortex generator;
d") vortex occurrence feature width;
St))) Strohal number streuhal (dimensionless constant).
S. The value of vortex generator width d and Reynolds number Re.
When the Reynolds number Re<2@104, S. The variable; Re in 2@104-
Within the range of 7@106, S. The value remains essentially the same, this range is the basic measurement range of the flow meter.
Equation (1) shows that when d and St are constant, the frequency f generated by the vortex is proportional to the average velocity v of the fluid and the temperature of the fluid.
Pressure, density, composition, viscosity and other parameters are irrelevant. Therefore, the average flow rate v of the fluid can be obtained from the frequency f generated by the vortex to achieve the purpose of measuring the flow rate Q of the fluid in the pipeline.
v=fSd(2)
Q=vS=fSd(3)
(31 in S is the cross-sectional area of ​​the pipe.
Sds is a constant, let = go = s, then Q = f/K. In the formula, K is the meter coefficient (pulse/liter) of the flow meter, which is usually determined by the actual flow rate test.
As the vortex is generated alternately on both sides of the vortex generating body, the vortex force acts on the detection body to generate an alternating stress that acts on the electric element and generates an alternating charge signal having the same frequency as the vortex, and is processed by the converter. After that, the pulse signal with the vortex frequency or the 4-20mADC signal proportional to the flow rate is output to the secondary instrument for accumulation and display.
2 The selection of vortex street flow is generally divided into two types: selection of model and choice of caliber.
2.1 Selection of models The flowmeters with different structures are selected according to the use environment and the fluid to be measured. When the ambient temperature around the flowmeter is less than 60e, the flowmeter can select the combination type. When the ambient temperature of the flowmeter is higher than 60e, the separation type must be selected.
When the use environment is flammable and explosive, flameproof or intrinsically safe type is selected according to explosion-proof grade. The general environment is generally selected.
According to the acquisition signal requirements to choose different output formats, when the need for flow accumulation can choose pulse output type or analog (4-20mA
DC) output type, select analog (4-20mADC) output type when control is required.
2.2 The choice of caliber The caliber of the vortex flow sensor should be reasonably selected based on the flow rate and flow rate, and it does not necessarily have to be the same diameter as the process piping. Due to the wide flow range of vortex flowmeters, the choice of caliber is mainly for lower limit flow. The lower limit of the general liquid flow rate is 0.5m/s. The gas is selected within the range of 4-5m/s. The normal flow rate is preferably between 1/2 and 2/3 of the measurement range. In general, the sample selection provided by the flowmeter manufacturer only gives the flow measurement range of commonly used fluid water, compressed air, and saturated steam. Other fluids need to select the flowmeter diameter through calculation. Omitting this point will often cause flowmeters. Not used properly.
According to the results of multiple selections, the author believes that the appropriate reduction of the flowmeter aperture will increase the idle speed and Reynolds number, so that the meter constant will be completely linear, which can improve the accuracy of the instrument and also help to adjust the signal amplifier.
3 The vortex flowmeter should be installed in a place that is insulated, ventilated, and easy to maintain. It should be installed as far away as possible from vibration sources and where electromagnetic interference is strong. Vibration must be used in places where vibration exists to reduce the influence of vibration on the pipeline.
Vortex flowmeters can be installed horizontally, inclined or vertically on the pipeline. The installation position should be noted that when the vertical installation, the liquid medium must flow from bottom to top: when installing the temperature, pressure sensor or flow Control Valve on the pipeline, the temperature, pressure sensor and regulating valve should be installed downstream of the flowmeter.
Before and after the vortex flowmeter must have a sufficiently long straight pipe section, see Table 1 for specific requirements. The inner diameter of the pipe to be equipped must also be the same as the inner diameter of the vortex flow transmitter. The inner diameter of the seal connected to the pipe must be slightly larger than the inner diameter of the sensor, and the seal cannot protrude into the pipe.
Table 1 upstream pipe form and straight pipe length requirements straight pipe length requirement f min)
Upstream Pipeline Upstream Concentric Shrinking Full Open Valve 15D5D
One 9 (b elbow 20 DSD
Concentric Expansion 25DSD
Same plane two 9 (b elbow 25DSD
Different planes two 9 (b elbow 40D5D
Regulating valve half open valve 50DSD
The flow meter power supply is +24VDC. The shielded signal cable is used for the connection cable. Keep away from the strong power supply cable when wiring and try to use a separate metal protection sleeve. The grounding should be reliable.
4 Precautions In order to allow this type of instrument to better serve the flow measurement in the chemical industry, according to the practice of our plant in recent years, the following aspects should be given enough attention by the relevant measurement management and use departments.
4.1 Instrument selection Chemical industry fluids are more f steam, gas, water, hydrogen, etc., the pipeline thickness of the transmission fluid varies greatly (DN15-DN300), the physical properties of the fluid (such as temperature, pressure, density, viscosity) and The chemical properties (corrosiveness) are also very different, and the flow fluctuations are larger. Therefore, the selection of vortex flowmeters is the first and the most important one. To this end, two basic principles should be grasped during the selection process: one must ensure production safety, and the other must ensure the accuracy of use. The chemical industry first considers that the explosion-proof performance of vortex flowmeters must meet the site requirements, and must be followed by three selection parameters, namely, the maximum, minimum, and common instantaneous flow rates in the near and far future (mainly used for the size of the selected instrument 1 The design pressure of the medium to be measured is mainly used for the nominal pressure level of the selected instrument and the working pressure f is mainly used for the pressure level of the selected instrument pressure sensor.
4.2 Verification (calibration)
At present, there are still some difficulties in the on-site verification of vortex flowmeters. For flowmeters used for large-scale trade measurement or important process control and other important occasions, the site does not have the on-line calibration conditions, and it is not possible to determine whether the performance of the meter is qualified only by the manufacturer's factory qualification certificate. Therefore, in order to ensure the accuracy and reliability of the measurement results of the instrument in the future work process, it is necessary to send it to an organization with qualification (calibration) qualification for verification before installation (Calibration 1.
4.3 Process installation The correct selection of the installation point and the correct installation of the sensor are all very important steps. If errors occur in the installation, the light affects the accuracy of the measurement, and seriously affects the service life of the instrument, resulting in damage to the instrument. Avoid vibration and high-temperature and high-heat environments as much as possible, and keep away from interfering components (such as compressors, separators, pressure regulators, heads, and headers, elbows, etc.). Keep concentric and straight sections of the straight pipe section of the meter straight and straight to ensure that it is measured. The medium is a clean single-phase fluid.
4.4 Parameter Setting The meter factor of the flow meter is verified under laboratory conditions. When used on site, the meter factor should be corrected. For supporting secondary instruments (intelligent flow totalizer 1 parameter settings, configuration work and flow measurement network in the various parameter settings, software design should meet the process and flow meter requirements.
4.5 Late-stage management In order to ensure the accuracy and reliability of long-term instrumentation and avoid unplanned outages and data loss, daily management and cycle maintenance of the instrument itself and the entire flow system must be strengthened after the vortex flowmeter is put into operation. Such as periodical metrological data (daily or weekly), daily inspections, systematic calibrations (1-2 years), inspection of instrumental factors, etc.
4.6 Internal Maintenance Due to dirty fluid or other reasons, the instrument's measuring chamber and its components must be checked or cleaned regularly. For vortex flowmeters of the same specifications, the core components such as vortex generators and diversion fluids cannot be interchanged. Otherwise, the metering coefficients must be recalibrated and the temperature and pressure of the vortex flowmeters must be calibrated for the sensors.
5 Problems exist Because vortex flowmeters are essentially fluid vibrating flowmeters, they are particularly sensitive to external vibrations and fluid flow conditions. Not only can the sensor experience vortex forces, but it can also sense other forces on the sensor, such as pipeline vibrations, impact forces from pipeline fluids, and random pulsating pressures due to changes in fluid pressure. Will have a great influence. Especially in the case of small flow measurement, the small lateral flow generated by the small lift force, the detection signal is weak, very vulnerable to fluid shock vibration noise and pipeline vibration noise. That is, the ability of this kind of instrument to resist interference needs to be further improved.
In addition, due to the short time for the vortex flowmeter to be put on the market, the reliability and stability of the instrument have yet to be tested in a variety of complex conditions: the sensitivity of the measurement accuracy to the flow state and the medium contamination remains to be studied: on-site verification methods Need to be further explored.
The above is the introduction of Xiaobian Xinxin's "Application of vortex flowmeters in flow measurement in the chemical industry". I hope that I can help you and look forward to cooperating with you! wish you a happy life!
Application of Vortex Flowmeter in Flow Measurement of Chemical Industry
Vortex flowmeter is a very commonly used measuring flow element in industrial production, which has important significance for industrial production. At present, vortex flowmeters are widely used in various industrial production, and the effect of measuring flow rate is very significant. This article will briefly describe the application of Huaning vortex flowmeters in flow measurement in the chemical industry.