How to choose a vortex flowmeter

Abstract: The information on how to select the vortex flowmeter is provided by the excellent flowmeter and flowmeter manufacturers. With the development of flow measurement technology, vortex flowmeters have been used more and more. However, due to the short use time of such flowmeters, many problems are often encountered in actual selection. The article briefly describes the vortex flowmeter. The working principle of the flow meter is given. For more flowmeter manufacturers to select models and price quotations, you are welcome to inquire. The following is the details of the article on how to select a vortex flowmeter. With the development of flow measurement technology, vortex flowmeters have been used more and more. However, due to the short use time of such flowmeters, many problems are often encountered in actual selection. The article briefly describes the vortex flowmeter. The working principle of the flowmeter, and specific recommendations for selection and use are given. Vortex flowmeter is a new flow meter with contemporary advanced level. It is a natural oscillation type flowmeter developed in the late 1970s and early 1980s. It has the advantages of simple structure, convenient installation and maintenance, many types of applicable fluids, high accuracy, wide flow range, small pressure loss, etc., and has been widely used in a short period of time. However, due to the short application time, there is little theoretical research and practical experience in application. According to the years of use in our factory, it has been proved that reasonable selection and use are the key to the application of this flowmeter. 1 The working principle of the flowmeter When a nonlinear object is placed in the flow field, it will alternately separate behind the object and release two columns of regular staggered vortices. This vortex is called“Karman Vortex Street”. A bluff object is called a vortex generator. Within a certain flow range, the vortex separation frequency is proportional to the average flow velocity (flow) in the pipeline. The vortex separation frequency can be detected through various forms. The flow rate of the fluid can be measured. Average flow rate of incoming media. , the width of the upstream surface of the vortex generator is d, then there is the following relationship: where f is the vortex street frequency; d is the width of the vortex generator; , is the incoming flow velocity; s is the Strouhal number; d is the diameter of the body. s, is a dimensionless number, for a certain vortex generating body, the Strouhal number s; and the Reynolds number r. When the Reynolds number r. In 2x104 a 7xro“When the Strouhal number s is within the range, it can be considered as a constant. From formula (1), it can be known that under the known conditions of the width d of the vortex generating body onward flow surface and the Strouhal number 5; the average flow velocity of the fluid in the pipeline can be determined by measuring the separation frequency of the sensor. and volume flow. 2 Selection of vortex flowmeter When choosing a vortex flowmeter, the temperature and pressure of the measuring medium should be paid attention to first, and the selected instrument must be able to adapt to the actual temperature and pressure. Secondly, choose the appropriate diameter. If the diameter is too large, it will not only increase the cost, but also cannot exert the ability of the flowmeter, and the measurement data will be inaccurate; if the diameter is too small, the pressure drop will be too large, or cavitation will appear. This will affect the meter accuracy. In addition, overspeed can also affect the life of the instrument and cause mechanical damage. Before the vortex flowmeter is selected, the flow of the pipeline medium should be calculated to determine whether the actual working flow will exceed the measurement range of the selected flowmeter. Under normal circumstances, the maximum working flow (velocity) in the pipe will not exceed the measurement upper limit of the vortex flowmeter (50 s for air, 70 s for steam, and 7 m/s for water). Therefore, only the minimum flow of the pipeline medium needs to be calculated. If the vortex flowmeter is used for gas measurement, since the vortex flowmeter measures the volume flow in the use state, and the flow value generally provided is often the flow value in the standard state, therefore, the standard state needs to be converted into Working state (liquid is generally not considered because it is an incompressible fluid). The conversion formula is as follows: where q. For the working state flow, m3/h; q. is the standard state flow, expansion/h; p, is the working state pressure, pa; now is the working state temperature, °C; t. is the standard state temperature, °C (Note, t. is generally 20 °C). The minimum flow rate of the vortex flowmeter is generally limited by the following factors: (l) Limited by the Reynolds number of the flow field, as mentioned earlier, when the Reynolds number r of the flow field.>At 2x104, the Strouhal number sr is a constant, and the generated vortex frequency has a linear relationship with the flow velocity, so the Reynolds number re>2x104 is the basic working condition of the vortex flowmeter, when the Reynolds number r.<At 2x104, even if vortices are generated and can be detected, the measurement data of this flowmeter is erroneous. (2) The limitation of vortex energy, when the flow rate of the fluid medium is low, the vortex strength is not enough (vortex strength and lift sand’Proportional relationship), the rotation speed of the vortex is also low, and cannot generate enough lift. For piezoelectric detection, especially magneto-sensitive detection, the energy is not enough to cause deformation or vibration of the sensitive element, and it cannot generate a signal, even if the Reynolds number is r. It can meet the detection requirements but cannot realize the detection, and the instrument still cannot work. (3) When measuring liquid medium, it is also necessary to check whether the minimum working pressure is higher than the saturated vapor pressure at the working temperature, that is, whether cavitation occurs. If cavitation occurs, the flowmeter cannot work. Even if it can work, the measured value is biased. big.

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