Flow meter calibrator

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1. How to slow down a steam flow meter? Steam flow meters are generally pressure differential flow meters, which convert the flow rate based on the pressure difference before and after the flow meter. The greater the pressure difference, the greater the flow rate, and the smaller the pressure difference, the smaller the flow rate. Therefore, if you want the steam gauge to run slowly, you need to find a way to reduce the pressure difference between the two sides of the differential pressure sensor. Generally, the high-pressure side is located in front of the flowmeter, and the low-pressure side is located behind the flowmeter, which can cause the flowmeter reading to decrease or even become negative. So the flowmeter calibrator is designed to adjust the interference pulse signal emitted by the sensor of the flowmeter to promote slow rotation caused by pressure difference between the sensors on both sides. The principle of the vortex flowmeter is: 1. The generation and phenomenon of Karman vortex street. To illustrate the generation of Karman vortex street, lets consider the flow of viscous fluid around a cylindrical body When the fluid velocity is very low, the fluid has zero velocity at the front stagnation point, and the incoming flow flows along the left and right sides of the cylinder. In the front half of the cylinder, the velocity gradually increases and the pressure decreases, while in the back half, the velocity decreases and the pressure increases. At the rear stagnation point, the velocity is zero again At this point, the flow is the same as that of an ideal fluid flow cylinder, with no vortex generated, as shown in Figure 3-7a As the inflow velocity increases, the pressure gradient in the rear half of the cylinder increases, causing separation of the fluid boundary layer, as shown in Figure 3-7b When the Reynolds number Re of the incoming flow increases further and reaches around 40, a pair of symmetric vortices with opposite rotation are generated at the separation point S of the boundary layer due to greater obstruction of the fluid micro clusters in the boundary layer of the rear half of the cylinder As shown in Figure 3-7c Within a certain range of Reynolds numbers Re, the frequency of stable Karman vortex streets and vortex shedding is directly proportional to the fluid flow velocity Figure 3-7 Schematic diagram of cylinder vortex street generation. 2. The stability conditions of Karman vortex street are not always stable under any conditions Von Karman has theoretically proven that the stable vortex street condition is: the distance between two columns of vortices in the vortex street is h, and the distance between two vortices in a single column is. If the relationship between the two satisfies=1 or h/=0.281 (3-24), the generated vortex street is stable.

3. To derive the relationship between vortex shedding frequency and flow velocity, the motion velocity of the vortex street itself must first be obtained For the sake of discussion, we assume that the source upstream of the vortex generator is an irrotational and stable flow, with a velocity circulation of zero According to Thomsons theorem, the velocity circulation of the two corresponding vortices generated downstream of the vortex generator must be equal in magnitude and opposite in direction, with a combined circulation of zero. Due to the opposite rotation direction and equal velocity circulation of the two corresponding vortices, the vortex street will m

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