Vacuum force factors (vacuum created by a "flow through" liquid)

[Ralphamale01]

TL;DR

How is vacuum related to surface area?

Greetings all,

I'm new here and hope I'm asking this in the correct thread. So, the question is; where you have a vacuum created by a "flow through" liquid witin a large diameter container exerting suction force upon a smaller diameter input tube submerged in a liquid, does the surface area of the container determine how much vacuum is developed, or is the depth (weight) of liquid in container an equal, greater or minimal factor? Please see attached sketch. Thank in advance for any help.

 

[Baluncore]

Welcome to PF.

A vacuum is limited by atmospheric pressure, and the vapour pressure of the liquid.

The area of the wall is NOT important, because pressure is a force per area.

The most important thing is the depth, density and hydrostatic pressure. That is the force of liquid per unit area, which increases with depth.
https://en.wikipedia.org/wiki/Hydrostatics#Pressure_in_fluids_at_rest

 

[Ralphamale01]

Welcome to PF.

A vacuum is limited by atmospheric pressure, and the vapour pressure of the liquid.

The area of the wall is NOT important, because pressure is a force per area.

The most important thing is the depth, density and hydrostatic pressure. That is the force of liquid per unit area, which increases with depth.
https://en.wikipedia.org/wiki/Hydrostatics#Pressure_in_fluids_at_rest

Understood, Thank You!

 

[Merlin3189]

In hydraulics, life is very easy because the pressure varies within the liquid simply in proportion to the depth.
So in your case, as liquid flows out the tank, the air layer gets expanded, its pressure reduces and water is "sucked" up the tube. This can continue until the depth of water in the pipe matches the depth of water in the tank.
The pressure in the air pocket will have reduced by the depth x density of liquid, so now the atmospheric pressure is just enough to stop the liquid pushing out of the tank and to support the liquid in the tube.

As an interesting (IMO) sidenote, if there had not been any air pocket at all - the pipe and tank had started completely filled with liquid - then the liquid would not drain out of the tank at the bottom, rather the liquid would flow down the pipe. Air would enter the tank from below until it had filled the horizontal pipe and enough of the vertical pipe to equalise the depths in pipe and tank.

 

[Ralphamale01]

In hydraulics, life is very easy because the pressure varies within the liquid simply in proportion to the depth.
So in your case, as liquid flows out the tank, the air layer gets expanded, its pressure reduces and water is "sucked" up the tube. This can continue until the depth of water in the pipe matches the depth of water in the tank.
The pressure in the air pocket will have reduced by the depth x density of liquid, so now the atmospheric pressure is just enough to stop the liquid pushing out of the tank and to support the liquid in the tube.

As an interesting (IMO) sidenote, if there had not been any air pocket at all - the pipe and tank had started completely filled with liquid - then the liquid would not drain out of the tank at the bottom, rather the liquid would flow down the pipe. Air would enter the tank from below until it had filled the horizontal pipe and enough of the vertical pipe to equalise the depths in pipe and tank.

Thank you Merlin for your kind reply!