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1. Working principle of vortex flowmeter
1. Placing a triangular vortex generator in the fluid will cause regular vortices to alternate on both sides of the vortex generator, which is called Karman vortex. These vortices are arranged in an asymmetric manner downstream of the vortex generator to form vortex columns.
2、 The vortex flowmeter measures the volumetric flow rate, standard state volumetric flow rate, or mass flow rate of gases, vapors, or liquids based on the K á rm á n Vortex Street principle, and can be integrated as a flow transmitter into automated positive osmosis control systems.
3、 Vortex flowmeter uses the principle of fluid oscillation to measure flow rate. When a fluid passes through a vortex flow transmitter, two alternating columns of vortices are generated behind the vortex generator, whose frequency is proportional to the average velocity of the fluid flowing through the vortex generator and the characteristic width of the vortex generator. The release frequency of a vortex can be expressed as: f=(v/d) * St, where f is the frequency (in Hz), v is the average velocity of the fluid (in m/s), d is the characteristic width of the vortex generator (in m), and St is the Strouhal number, which is usually a dimensionless value between 0.14 and 0.27.
4、 The Strouhal number St is a function of the Reynolds number Re, and within a specific range of Reynolds numbers, the value of St is approximately 0.2. In practical measurements, it should be ensured that the Reynolds number of the fluid is within this range, and the vortex frequency is proportional to the fluid velocity.
5、 By measuring the vortex frequency, the average velocity v of the fluid flowing through the
2. Actual flow rate of vortex flowmeter
The flow formula measured by vortex flowmeter is qv=π D2U/4=π D2mdf/4Sr K=f/qv=[π D2md/4Sr] -1. Under specific flow conditions, a part of the fluid kinetic energy is converted into fluid vibration, and the vibration frequency of the vortex flowmeter is proportional to the flow rate (flow rate). A flowmeter that works based on this principle is called a fluid vibration flowmeter.
. At present, there are three types of fluid vibration flow meters: vortex street flow meters, vortex precession flow meters, and jet flow meters. Fluid vibration flowmeter has the following characteristics: 1) The output is a pulse frequency, which is proportional to the actual volumetric flow rate of the measured fluid and is not affected by fluid composition, density, pressure, or temperature; 2) The measurement range is wide, and the general range can reach 10:1 or more; 3) The accuracy is above average level; 4) No movable parts, high reliability; 5) The structure is simple and sturdy, easy to install, and has low maintenance costs; 6) Widely applicable, suitable for liquids, gases, and vapors. The working principle is to set up a vortex generator (blocking fluid) in the fluid, and generate regular vortices alternately from both sides of the vortex generator. This type of vortex is called a Karman vortex street, as shown in Figure 1. The vortices are arranged asymmetrically downstream of the vortex generator. Assuming the frequency of vortex occurrence is f, the average velocity of the measured
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