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How to measure the flow of gas-liquid two-phase fluid

As can be seen from the information provided by the manufacturer, there are several instruments that can be used to measure the flow of two-phase fluids with a low concentration of discrete phases. There are some examples of successful applications from users, but the current flowmeters are all in single The measurement performance is evaluated in the phase flow state. There is no flowmeter for single-phase flow calibration to measure the system variation of two-phase flow. Therefore, it is not clear how much error such application brings. Some sporadic data and some qualitative analysis.
1 electromagnetic flowmeter, when the liquid contains a small amount of gas, the distribution of gas in the liquid is tiny bubbles. At this time, the electromagnetic flowmeter can still work normally, but the measured volume flow of the gas-liquid mixture. When the amount of gas contained in the liquid increases, the bubble geometry gradually increases, and then transitions to the elastic structure. When the size of the bubble is equal to or larger than the size of the end face of the flowmeter electrode and is swept from the electrode, the electrode may be covered by the gas, causing the circuit to be momentarily disconnected, output sloshing, or even malfunction.
2 Coriolis mass flow meter. Manufacturers often claim that liquids containing a few percent by volume of free gas have little effect on the normal measurement of Coriolis mass flow meters, such as ice cream and similar emulsions when the bubbles contained in the liquid being tested are small and uniform. May be right. However, the experimental results are not optimistic. According to the relevant literature, the Italian Metrology Institute's impact on the gas content of seven types of Coriolis mass spectrometers shows that some models have no obvious influence when containing 1% (volume ratio) of bubbles, and some models have errors of 1% to 2%. One of the double-tube models is as high as 10% to is%; when the bubble is 10%, the error is generally increased to is% to 20%, and individual models are as high as 80%. It can be seen that the different measuring tube structures and different types of Coriolis flowmeters are greatly affected by the gas content, and the test data of one model cannot be extended to other models.
3 ultrasonic flowmeter. The Doppler ultrasonic flowmeter works as described in Section 3.3.2 and is primarily used to measure liquids containing particles or bubbles that give a strong amount of strong reflection. This type of meter measures only the volume flow rate or the average flow rate inside the measuring tube. If mass flow is to be measured, a fluid density meter is added.
Since such meters detect the flow velocity of discontinuous points (ie, bubbles), there is uncertainty between the measurement results and the average flow velocity in the pipe due to the inconsistency of the flow velocity at each point in the flow cross section, resulting in measurement performance. Poor. The uncertainty is generally only ± (1% ~ 10%) FS, and the repeatability is (0.2% ~ 1%) FS.
The upper limit of the bubble content applicable to the Doppler ultrasonic flowmeter is much larger than the propagation time method, but it is also limited. Especially when the diameter is large, the bubble content is too high, and the ultrasonic signal is so attenuated that it cannot be measured. Therefore, the selection should be cautious and consult the manufacturer in advance.

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