pressure transducer on double compaction tank

[Chryses]

Good evening, everyone.

I am designing a tank (see simplified drawing in attachment) so composed:

• 2 connecting compartments via an external bypass
• the lower compartment is equipped with a vent for air
• the shell that divides the 2 compartments is a little smaller and is welded to a ring, welded in turn, to the cylindrical walls of the tank
• on the bottom of the tank, then in the lower compartment, a membrane pressure transducer is installed

now the question is:
on the transducer weighs the pressure of all the liquid inserted in the tank or only that of the lower compartment?

because there is a small discussion on the distribution of pressure inside the tank.
I argue that the load of the liquid of the upper compartment is discharged on the walls of the tank through the support ring, so the pressure of the lower compartment is "independent" from that of the upper compartment.

How do you see it?

 

[exxon]

the fact that the separator set is smaller, larger, bombed or not, nothing changes. with this assumption, changing the design to make it more schematic, the situation translates as follows.
the pressure (relative to the environment) measured by the sensor is given by the volume mass of the fluid multiplied by the piezometric height h.

always that:
1. the upper compartment is communicating with the outside (otherwise to the previous pressure it is necessary to sum the (relative) pressure of the gas that overrides the fluid).
2. the free fur of the fluid is above the outer siphon. if you are below, then you need to specify a set of particular cases.

 

[cacciatorino]

now the question is:
on the transducer weighs the pressure of all the liquid inserted in the tank or only that of the lower compartment?

If the divider is rigid, in the lower compartment only see the pressure due to the liquid level in that compartment.

 

[exxon]

If the divider is rigid, in the lower compartment only see the pressure due to the liquid level in that compartment.

no, it is not so: the external siphon balances the pressure between the two compartments. if the free fur is above the phosphorus, all the piezometric height contributes to the pressure detected by the sensor.

 

[cacciatorino]

no, it is not so: the external siphon balances the pressure between the two compartments. if the free fur is above the phosphorus, all the piezometric height contributes to the pressure detected by the sensor.

You're right, I missed the fact of the "external by-pass."

 

[Chryses]

Good morning!

but I see you already have clear ideas, thank you!

the upper compartment is equipped with pyrophymatic vent, so the tank never goes in overpressure.
actually represented so more simply I find it easy to guess that the pressure is given by the height of the liquid above, which is the sum of the 2 compartments.

But what if I put a valve in the outside bypass?
therefore taking the exxon schema and leaving the liquid level exactly where it is represented, applying the reasoning of the pressure balance happens that

1. if the valve is open the reasoning is the same, the level of the liquid that weighs on the pressure plate is the one indicated in the scheme
2. But if the valve is closed? Does the pressure change and exclude the area above? Just shut the valve and change the pressure?

This puts me some doubts

 

[exxon]

open valve, the pressure sensor sees two distinct free hairs: that inside the upper tank and that inside the vent pipe. for the well-known rule of communicating vessels, if from any point in a fluid I see two distinct free hairs, these must coincide (peli Free, therefore with the same ambient pressure above them...). This is the first case analysed.

if I close the valve, the sensor sees the only free fur inside the vent, but no more than the tank. However, since the valve closure does not result in fluid shifting, the two free hairs continue to coincide and the sensor does not change its reading.

the above is described by the following figures.
if I now change the amount of fluid in one of the two compartments (at this separate point), the sensor will continue to read the pressure determined by the only free fur "in sight", which turns out to be that in the vent pipe.

in the example of the following figure, the addition of fluid in the upper compartment does not change the level in the lower one and therefore not even the reading of the sensor.

 

[antonio_sc]

if the divider is rigid

Excuse me if I interfere in the discussion but I have a curiosity about it. If it wasn't, what if the divider wasn't rigid? a portion of the load would be weighed on the liquid placed in the lower compartment, right?

 

[bip]

That's right.