The principle of vortex flowmeter

In the 1980s, people generally used standard orifice flowmeters for saturated steam flow measurement. However, from the perspective of the development of flow meters, although the orifice flowmeter has a long history and a wide range of applications, people have also studied it the most and have the most experimental data. It is perfect, but there are still some shortcomings when using a standard orifice flowmeter to measure the saturated steam flow: First, the pressure loss is relatively large; the saturated steam flow measurement was generally used in the 1980s by the standard orifice flowmeter, but from In terms of the development status of flow meters, although the orifice flowmeter has a long history and a wide range of applications; people have studied it the most and the test data is the most complete, but it still exists when a standard orifice flowmeter is used to measure the saturated steam flow. Some shortcomings: First, the pressure loss is large; Second, the pressure guiding tube, the three groups and the connection joints are easy to leak; Third, the range is small, generally 3 to 1, which may cause measurement due to large flow fluctuations The value is low. The vortex flowmeter has a simple structure, and the vortex transmitter is directly installed on the pipeline, which overcomes the leakage of the pipeline. In addition, the pressure loss of the vortex flowmeter is small, the measuring range is wide, and the measuring range ratio of saturated steam can reach 30 to 1. Therefore, with the maturity of vortex flowmeter measurement technology, the use of vortex flowmeter is more and more popular. 1. The measurement principle of vortex flowmeter The vortex flowmeter uses the principle of fluid oscillation to measure the flow. When the fluid passes through the vortex flow transmitter in the pipeline, the vortex generator of the triangular column alternately produces up and down proportional to the flow rate. Two rows of vortices, the release frequency of the vortex is related to the average velocity of the fluid flowing through the vortex generator and the characteristic width of the vortex generator, which can be expressed by the following formula: f u003d Stv/d where: f is the release frequency of the vortex, Hz; v is The average velocity of the fluid flowing through the vortex generator, m/s; d is the characteristic width of the vortex generator, m; St is the Stroha number, dimensionless, and its numerical range is 0.14-0.27. St is a function of Reynolds number, Stu003df(l/Re). When the Reynolds number Re is in the range of 102~105, the St value is about 0.2. Therefore, in the measurement, try to satisfy the Reynolds number of the fluid in the range of 102~105, and the vortex frequency fu003d0.2v/d. It can be seen that by measuring the frequency of the vortex, the average velocity v of the fluid flowing through the vortex generator can be calculated, and then the flow rate q can be calculated by the formula qu003dvA, where A is the cross-sectional area of u200bu200bthe fluid flowing through the vortex generator. When the vortex is generated on both sides of the generating body, the piezoelectric sensor is used to measure the alternating lift change perpendicular to the fluid flow direction, and the lift change is converted into an electric frequency signal, and then the frequency signal is amplified and shaped, and then output to the secondary Instrument, accumulate and display. 2. Application of Vortex Flowmeter 1. Selection of Vortex Flowmeter (1) Selection of Vortex Flow Transmitter Our company uses VA piezoelectric vortex flow changer produced by Hefei Instrument General Factory in saturated steam measurement. Because of the wide range of the vortex flowmeter, in practical applications, it is generally considered that the flow rate of the saturated steam should not be lower than the lower limit of the vortex flowmeter, which means that the fluid flow rate must not be less than 5m/s. . Vortex flow transmitters of different calibers can be selected according to the amount of steam used, and the caliber of the transmitter cannot be selected based on the caliber of the existing process pipeline. (2) The selection of pressure compensation pressure transmitter. Because the saturated steam pipeline is long and the pressure fluctuates greatly, pressure compensation must be adopted. Considering the corresponding relationship between pressure, temperature and density, only pressure compensation can be used in the measurement. The saturated steam pressure of the company's pipeline is in the range of 0.3-0.7MPa, and the range of the pressure transmitter can be selected as 1MPa. (3) Display instrument selection. The intelligent flow indicator of the display instrument has the functions of temperature and pressure compensation, instantaneous flow display and cumulative flow accumulation. 2. Most settings of the vortex flowmeter (1) The setting of the instrument system, the instrument coefficient K that Hefei Instrument General Factory needs to set can be expressed by the following formula: Ku003d1000/K0 where: K0 is the vortex generator The instrument constant calibrated when leaving the factory is L/pulse; the unit of k is the number of pulses/m3. (2) Range setting of pressure compensation pressure transmitter. (3) Pressure and flow alarm upper limit setting. 3. Installation of vortex flowmeter (1) The vortex flowmeter should be installed as far away as possible from vibration sources and strong electromagnetic interference. Vibration damping devices must be used where vibration exists to reduce the impact of vibration on the pipeline. (2) The configuration of the straight pipe section, the front and rear straight pipe sections must meet the requirements of the vortex flowmeter, and the inner diameter of the pipeline must also be the same as the inner diameter of the vortex flow transmitter. 4. Precautions for using the vortex flowmeter to minimize the impact of the steam hammer in the pipeline on the vortex generator. When the vibration is large and cannot be eliminated, it is not suitable to use a vortex flowmeter. 3. Concluding remarks After the vortex flowmeter was put into use in our company, it overcomes many shortcomings of the original orifice flowmeter. The measurement of saturated steam is more accurate and stable, and maintenance is convenient. However, it is worth noting that the flow rate of saturated steam fluid cannot be measured. Below 5m/S, otherwise, the flow rate will be low.