The flow rate is a dynamic quantity, and the measurement process is related to the fluid activity, the physical properties of the fluid, the working conditions of the fluid, and the length of the straight pipe before and after the flow meter. Therefore, it is concluded that the flow measurement method and the selection of flow appearance should sum up the influence of the above factors.
The flow of flowmeter is a dynamic quantity. The measurement process is related to the fluid activity, the physical properties of the fluid, the working conditions of the fluid, and the length of the straight pipe before and after the flow meter. Therefore, it is concluded that the flow measurement method and the selection of flow appearance should sum up the influence of the above factors.
The kinetic parameters of fluid activity, such as velocity and momentum, are directly related to the flow rate. Therefore, the physical effects caused by these parameters can be used as the physical basis for flow measurement. At present, have cast varieties used flowmeter is complicated, its measuring principle, layout characteristics, scope and usage is different, so the classification according to the different principle of distinction. There is no consistent classification method,
A points according to measurement method
Flow measurement according to the measurement method can usually be divided into volumetric method, speed method (flow method) and mass flow method of 3.
A volume method
Volume method refers to a container with a standard volume of continuous measurement of the measured fluid, and in a unit (or a period of time) to measure the volume of the standard method of calculating flow. This method of measurement is less noisy due to its active condition, so it is suitable for measuring fluids with high viscosity and low Reynolds number. But it is not suitable to measure the flow rate of high temperature, high pressure and dirty medium. The upper limit of flow measurement is smaller. Typical surface has oval gear meter, waist take volume meter, scraper flowmeter and so on.
B velocity method
Velocity method refers to the method of calculating flow according to the uniform flow velocity on the cross section of a pipe. Various physical phenomena related to flow velocity can be used to measure flow rate. The mass flow can be obtained if the density of the fluid to be measured is measured again.
The throttling flowmeter has a long history and the most skillful technique in the velocity method flow meter. It is the most widely used flowmeter in the industrial production and scientific experiments. In addition, the flow meters measured by velocity method include rotor flowmeter, turbine calorimeter, electromagnetic flowmeter, ultrasonic flowmeter and so on.
Because this method is used to calculate the flow rate of uniform flow, so it is greatly affected by the conditions of the pipeline, such as Reynolds number, eddy current and cross section velocity asymmetry, etc., will bring errors to the measurement. But this measurement method has wide application conditions. It can be used for the measurement of high temperature and high pressure fluid. Some instruments can also be used to measure the flow of dirty medium. At present, the appearance of flow measurement using velocity method is widely used in industry.
C mass flow method
Both the volumetric method and the velocity method are required to give the density of the fluid to obtain mass flow. The density of the fluid is affected by the fluid condition parameters (degree of retreat, pressure), which will inevitably bring errors to the measurement of mass flow. One way to deal with this problem is to measure the volume flow and density of the fluid, or to compensate the change of fluid density based on the parameters of the fluid pressure and temperature obtained by the measurement. But the more desirable method is to measure the mass flow directly. The physical basis of this method is to measure the physical quantities related to fluid mass (such as momentum, momentum, etc.), so as to obtain the mass flow directly. This method has nothing to do with the composition and parameters of the fluid. It has significant advantages. However, the current flowmeters are complex and expensive, and therefore restrict their use.
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