An introduction to the influence of periodic pulsating flow on the measurement accuracy of turbine flowmeters

Abstract: The introduction of the influence of periodic pulsating flow on the measurement accuracy of turbine flowmeters is provided by excellent flowmeter and flowmeter manufacturers and quotation manufacturers. Abstract: Almost all pipeline flows are resistant to stability, and there are always various disturbances whether it is laminar flow or turbulent flow. If a certain parameter of the flowing fluid, such as pressure, velocity or density, bursts and changes continuously, the flow is called pulsating flow. More flowmeter manufacturers choose models and price quotations. You are welcome to inquire. The following is an introduction article detailing the impact of periodic pulsating flow on the measurement accuracy of turbine flowmeters. Almost all pipeline flows are resistant to stability, and there are always various disturbances in laminar flow conditions or turbulent flow conditions. If a certain parameter of the flowing fluid, such as pressure, velocity or density, bursts and changes continuously, the flow is called pulsating flow. The pulsating flow can affect the measurement accuracy of the instrument, and it will distort the measurement value when it is severe. Therefore, it is urgent in the industry to study the influence of the pulsation in the flow process on the measurement accuracy of the flowmeter. This article introduces the analysis of the influence of periodic pulsating flow on the measurement accuracy of turbine flowmeters for readers' reference. 1. The depletion method of pulsating flow measurement Almost all pipeline flows are stable, and there are always various disturbances whether it is laminar flow or turbulent flow. If a certain parameter of the flowing fluid, such as pressure, velocity or density, bursts and changes continuously, the flow is called pulsating flow. The pulsating flow can affect the measurement accuracy of the instrument, and it will distort the measurement value when it is severe. Therefore, it is urgent in the industry to study the influence of the pulsation in the flow process on the measurement accuracy of the flowmeter. Pulsations are everywhere, all the time, but they are extremely difficult to measure. It is almost impossible to measure the pulsating flow directly. We can only measure the primary parameters of the pulsation, such as amplitude, frequency and waveform, and then elucidate the influence of the pulsation on the output of the instrument from these parameters. Even measuring the parameters of the pulsation is not a trivial task. The only way is to use some special instruments to perform acoustic analysis on the fluid flowing in the pipeline to measure the pulsation parameters. If the pulsation frequency is low, and the upper limit of the frequency that can be used by the flow meter or pressure transmitter installed in the pipeline is not reached, the existence of the pulsation can be taught from the swing of the output pointer of the pressure meter. But to comprehend the value of each parameter of the pulsation requires specific measurements. After research, it was found that the pulsation was related to the flow velocity and had nothing to do with the static pressure. Therefore, the pulsation situation can be understood by measuring qVrms/qV (qVrms is the maximum pulsation value of the volume flow; qV is the average value of the volume flow). The following is the method to measure qVrms/qV: ① To measure the pulsation amplitude, it can be assumed that vrms/v≈qVrms/qV, v refers to the average flow velocity in the tube, and vrms is the maximum pulsation of the flow velocity in the tube. A thermal anemometer probe (hot wire or thermistor) can be inserted in the pipeline just upstream from the flow meter, and an in-line computer can be used to display the square of the maximum flow rate pulsation. ②When the flow meter is very close to the pulsation source (for example, in a place less than a quarter wavelength of the pulsation), the amplitude of the pulsation is the same as that of the pulsation source. Possible amplitudes can be estimated from changes in the volume, rotational speed, etc. of the pulsatile source. Although this method is not very reasonable, it does not need to use other instruments. ③ If the flow meter is a differential pressure meter, to derive the amplitude of the pulsation, it is necessary to measure the amplitude of the differential pressure pulsation Δprms/Δpps regardless of the throttle device, and the result will be used to roughly predict the amplitude of the pulsation. This value varies with the pulsation frequency, and the maximum possible value of qVrms/qV can be derived from the following equation: qVrms/qV≤Δprms/Δpps where: Δprms is the maximum pulsation of differential pressure, and Δpps is the differential pressure measured under steady flow. The raw data output by the flow transmitter is analyzed by spectrum, so as to obtain the pulsation pattern. Assuming that the pulsation frequency does not completely exceed the corresponding range of the flow transmitter, the pulsation frequency can be measured by the Fourier spectrum analyzer in the spectrum of the output signal. 2. Theoretical analysis of the influence of periodic pulsating flow on the measurement accuracy of turbine flowmeter 2.1 Construction of mathematical model and analysis of dynamic characteristics of turbine flowmeter When the pulsation frequency exceeds a certain range, the measurement value of the turbine flowmeter will have a large difference. . The origin of the difference pool mainly includes the following aspects: the resonance of the rotating blades, the meshing of the gears (the turbine flowmeter of the rigid output), the inertia of the rotating shaft and the gear, the shape of the pulsating flow, the frictional resistance of the rotating shaft, etc. Since the total pulsation is formed by the superposition of sine waves, the influence of periodic pulsation can be analyzed from the analysis of the influence of sine pulsation on the measured value of the turbine flowmeter. Both theory and practice show that when a sine quantity is involved in a time-invariant delusional system, the response in a turbulent state is a sine output quantity of the same frequency, but the amplitude and phase depend on the dynamic characteristics of the specific system.

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