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Vortex flowmeters are not suitable for measuring low Reynolds number fluids
2012-3-7 8:53:05

的使用条件的精确度对于液体大致在±0.5[%]R~±2[%]R,对于气体在±l[%]R~±2[%]R,重复性一般为0.2[%]~0.5[%]。 The accuracy of the use conditions of the vortex flowmeter is approximately ± 0.5 [%] R ~ ± 2 [%] R for liquids, and ± 1 [%] R ~ ± 2 [%] R for gas, and the repeatability is generally 0.2 [%] To 0.5 [%]. Because the meter coefficient of the flow meter VSF is low, the frequency resolution is low, and the larger the caliber is, the lower the caliber is. Therefore, the caliber of the meter should not be too large. Wide range is a characteristic of VSF, but what is important is the lower limit flow. Generally, the lower limit of the average flow velocity of liquid is 0.5m / s, and the gas is 4 ~ 5m / s. The normal flow rate of VSF is preferably 1/2 to 2/3 of the normal measurement range. The meter coefficient of VSF is not affected by the physical properties of the measurement medium. This is a great advantage. It can be applied to other media with a typical medium calibration, which is convenient for solving the problem of calibration equipment. However, it should be noted that the frequency range is also very different because the flow velocity ranges of liquid and gas are very different. In the amplifier circuit that processes the vortex signal, the passband of the filter is different, and the circuit parameters are also different. Therefore, the same circuit parameter cannot be used for different measurement media. When the medium is changed, the circuit parameters should be changed accordingly. The density of gas and liquid is very different, and the signal intensity generated by vortex separation is proportional to the density. Therefore, the signal strength is also very different. The gain and trigger sensitivity of the liquid and gas amplifier circuits are different. The piezoelectric charge is very different, and the parameters of the charge amplifier are also different. Even if the same gas has different media pressures and temperatures, different densities, different flow ranges and signal strengths, the circuit parameters must also be changed. Therefore, it is not feasible for a VSF to be changed without changing the hardware or software.

不适用于测量低雷诺数流体。 Vortex flowmeters are not suitable for measuring low Reynolds number fluids. When the Reynolds number is low, the Strouhal number changes with the Reynolds number, the instrument linearity becomes worse, and the high viscosity of the fluid will significantly affect or even hinder the generation of vortices. One limitation of the selection is that it cannot be used for the limit Reynolds number. under. Vortex flowmeters are suitable for a wide range of fluids, but pay attention to the dirty nature of the fluid. The scouring of the vortex generator by the fluid containing solid particles will generate noise and wear the vortex generator. If the contained short fibers are wound on the vortex generator, the meter coefficient will be changed. VSF has little application experience in miscible fluids. Generally, it can be used for dispersed and uniform micro-bubbles, but the volumetric gas content should be less than 7 [%] ~ 10 [%] for gas and liquid two-phase flow, if it exceeds 2 [ %] Should correct the meter coefficient. Can be used for gas-solid, liquid-solid two-phase flow containing dispersed and uniform solid particles with a content of not more than 2 [%]. It can be used for two-component liquid-liquid insoluble flow. Pulsating and swirling flow can severely affect VSF. If the pulsation frequency and the vortex frequency band are combined, it may cause resonance to damage the normal work and equipment, and cause the vortex signal to lock up. At this time, the signal is fixed at a certain frequency. Locking is related to the amplitude of the pulsation, the shape of the vortex generator, and the blockage ratio. VSF的正常工作的脉动阈值尚待试验确定。 The pulsation threshold of the vortex flowmeter VSF for normal operation has yet to be determined experimentally.