Let’s discuss whether the interfaces at both ends of a communicating vessel are identical, and whether a side-mounted interface gauge can reflect the true interface
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As the title suggests, if one wants to measure the interface inside a container, can instruments mounted on the side such as magnetic flip switches or float switches provide accurate measurements? The liquid level and interface inside the container are constantly changing; can the interface and liquid level in the bypass pipe remain consistent with those inside the container? I’ve searched for a lot of information on communicating vessels, but I’m still not sure about this question. Could someone who understands it explain it to me? Thank you!
Sure, it’s just the principle of communicating pipes; honestly, there’s not much to say about it
Magnetic flip plates and floats can be used to measure the level, requiring a density difference. The medium and whether the operating conditions are suitable also need to be considered. The bypass pipe can accurately reflect that, depending on the operating conditions of the medium, there may be certain delays or deviations.
The principle of a communicating vessel states that the liquid levels at both ends are equal when the medium is the same, but how can this be ensured in the case of mixed media? For example, in a 2-meter-high container equipped with a magnetic flap whose center distance is 1.8 meters, if water is first poured into the container to a depth of 1 meter and then gasoline is added up to a depth of 0.5 meters, will the liquid level inside the magnetic flap remain at the same level as that in the container? How does gasoline get into the magnetic flap? Even so, how can we ensure consistency across the two interfaces?
In a communicating vessel, according to the principle of pressure equilibrium, the average density in the large container changes; as a result, the liquid levels in the communicating vessel and the large container are not at the same height. You’ve seen those U-shaped connectors used to measure elevation levels. But for those idealists who keep singing the Internationale every day, for those stubborn people, as well as for those ungrateful ones, there’s still a solution: make a cut from top to bottom in the large container and weld in a fully continuous connector, and that way you can measure the elevation level. :lol
We have an oil-water separation tank on site, and it is necessary to measure the interface. A float level gauge is used for instrument selection. But the equipment feeds material in while discharging it at the same time, leaving no time for separation; since the oil and water are mixed together, it’s impossible to make any measurements. As mentioned on the 3rd floor, bypass systems generally have a certain degree of lag.
I also think that in most cases it’s basically impossible to measure accurately, unless the container is stirred thoroughly and the U-tube has many connection holes to maintain consistency
Design institutes prefer to make such choices. I asked the designers why they choose this approach and whether it can ensure consistency in the interface; their answer was that it’s likely possible. I believe that maintaining consistency in the interface requires very strict conditions, so I generally advise users to use top-mounted instruments that perform measurements directly inside the container
Statistically, consistency can be maintained; that is, after enough time, the liquid level (interface) remains equal； Dynamically, it is related to the resistance of the connecting pipeline and to the volume of the gauge chamber. The greater the resistance in the pipeline and the larger the volume of the gauge chamber, the larger the time constant becomes, and the worse the dynamic tracking performance is; in other words, it takes longer to achieve a consistent liquid level (interface).
Hehe. If the liquid in the lower layer does not descend below the lower connection port, then the liquid in the upper layer cannot enter the container.:lol If you keep thinking about it, there will be even more issues related to inconsistencies in the liquid levels. ——This is also the reason why a communicating vessel cannot measure interfaces.
Agreed, I think the same way. But some designers insist on designing it in that manner, which is why I initiated this discussion