Vortex flowmeter coefficient | Who can explain in detail the measurement principle of vortex flowmeter?

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1. Flow calculation formula for vortex flowmeter

A vortex generator (blocking fluid) is installed in the fluid, and regular vortices are alternately generated from both sides of the vortex generator. This type of vortex is called a Karman vortex street. Assuming the frequency of vortex occurrence is f, the average velocity of the measured medium flow is U, the width of the vortex generator face is d, and the diameter of the body is D. According to the principle of Karman vortex street, there is the following relationship: f=SrU1/d=SrU/md

(1), where U1- the average velocity on both sides of the vortex generator body, m/s； Sr Strouhal number; The ratio of the bow shaped area on both sides of the m vortex generator to the cross-sectional area of the pipeline

2. Factors affecting the instrument coefficient K of the vortex flowmeter

The main factors affecting the instrument coefficient K of the vortex flowmeter include changes in flow velocity and viscosity, accumulation, holding and wear, temperature changes, and differences in pipe diameter. The specific analysis is as follows: Changes in flow velocity and viscosity. The Reynolds number (Re) of fluids in industrial pipelines is usually greater than 2 × 10? At this point, the instrument coefficient K is stable. If the flow rate (v) decreases or the kinematic viscosity (y) increases, causing a decrease in Re to below the critical value (2 × 10?), the K value will undergo significant changes and produce nonlinear errors. By selecting a smaller diameter to increase the flow rate, Re can be maintained within a reasonable range to ensure a stable K value. If there are viscous particles or fibrous substances in the measured fluid, they may gradually

accumulate on the surface of the vortex generator, change its geometric dimensions, and affect the formation law of the vortex, resulting in K value deviation and measurement errors. Errors can be reduced by regularly cleaning the vortex generator or pre treating the fluid (such as filtering, separating impurities). If the edges of the worn triangular vortex generator are eroded or corroded by fluid, their geometric shape will be changed, resulting in changes in the K value. The impact of wear on K value can be reduced by selecting wear-resistant materials (such as ceramics, hard alloys) or optimizing column structure design (such as rounded transitions). The temperature change attenuation instrument coefficient K is usually calibrated at room temperature (about 20 ℃). If the fluid temperature significantly deviates from the calibration temperature, the thermal expansion and contraction effects will change the geometric dimensions (such as diameter and length) of the instrument body and vortex generator, thereby affecting the flow area and vortex separation frequency, resulting in additional errors in the K value. The K value needs to be dynamically corrected through software compensation formulas or calibrated in real-time using temperature sensors. If the inner diameter of the piping is slightly smaller than the inner diameter of the flowmeter (deviation ≤ 3%) during installation, although it will not directly change the K value of the instrument itself, it will cause additional errors due to sudden changes in the flow area, resulting in changes in the apparent flow velocity. It is necessary to improve measurement accuracy by adjusting the flow area or velocity parameters, or ensure that the inner diameter of the pipin

Vortex flowmeter coefficient | Who can explain in detail the measurement principle of vortex flowmeter?

1. Flow calculation formula for vortex flowmeter

2. Factors affecting the instrument coefficient K of the vortex flowmeter

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