Card mounted vortex flowmeter | Installation requirements for vortex flowmeter

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1. Vortex flow sensor

In the late 1960s, a new type of instrument that applied the principle of fluid vibration to measure flow, namely fluid vibration flowmeter, emerged successively. There are currently two types of vortex flow meters that have been applied, one is the Karman vortex flow meter that uses natural vibration, and the other is the vortex flow meter that uses forced vibration. This high-sensitivity flowmeter has no movable parts inside the pipeline, a long service life, a wide linear range, and is almost unaffected by changes in temperature, density, pressure, viscosity, etc. It has low pressure loss and high accuracy. The output of the instrument is a pulse signal proportional to the volumetric flow rate, which is suitable for gases and liquids, so it is quite popular. According to fluid mechanics, the Karman vortex is known to occur behind a nonlinear object, such as a cylinder, triangular prism, etc., when the flow sail body advances at a certain speed v, if a nonlinear object is placed vertically on the path of advancement, a vortex will form behind the nonlinear object, forming the Karman vortex street. If the object is a cylinder with a diameter of d, research has shown that the frequency of vortices occurring behind the cylinder is the same as in the design and use of hydraulic power head core drilling machines, where v is the flow velocity; D is the diameter of the cylinder; St is a dimensionless number related to the Reynolds number Re, known as the Strouhal number. The experiment can determine the relationship between St number and Reynolds number, as shown in Figure 7-24. From the relationship between Strouhal number and Reynolds number (logarithmic) of the cylinder in Figure 7-24, it c

an be seen that the St number remains almost constant in the range of Re=3 × 102 to 2 × 105, and is a constant number approximately equal to 0.21. Therefore, the frequency of vortex emission within this flow range can be written as the design and use of hydraulic power head core drilling rig. As can be seen from the above equation, the frequency of vortex emission is only related to the flow velocity v and cylinder diameter d, and is not related to the type, temperature, pressure, or density of the liquid. As long as the diameter d of the cylinder is appropriately selected, the above equation can always be satisfied. But when the Reynolds number exceeds 2 × 105, the St number is no longer a constant, and the above equation no longer holds. Therefore, this Reynolds number can be used to specify the upper limit of the flow velocity that can be measured. The lower limit of the measurable flow velocity is limited by the vortex detector. The Karman vortex is an asymmetric vortex street arranged alternately, as shown in Figure 7-25. The rotation direction of vortices is determined by the columns. If the rotation direction of the upper column of vortices is clockwise, then the rotation direction of the lower column is counterclockwise. The interval between the Karman vortex street columns is h, and the interval in the same column is l. The stable Karman vortex street satisfies the following relationship in the design and use of hydraulic power head core drilling machines. This conclusion was first theoretically proved by von Karman, and later verified by Karman and H. Rubach through experiments. The vortex flow sensor can be used for mud flow detection, which is suitable for flow measurement of various liquids, gases, and vapor

Card mounted vortex flowmeter | Installation requirements for vortex flowmeter

1. Vortex flow sensor

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