Water pressure in tank with open pipe
Water pressure in tank with open pipe
(OP)
We are trying to pressurise a tank of water to simulate (in a lab) pressure at approx. 5m deep in a river. If the tank is full of water and closed, apart from an open topped pipe that extends 5m vertically from the top of the tank, would the pressure 0.1 m down into the tank be: density of water x gravity(9.81) x 5.1m (assuming the pipe was full of water)? Does the diameter of the pipe above the tank have any effect on the water pressure in the tank?
The cross-sectional area of the tube is small in comparison to the tank. My understanding is that the pressure in the tank would be the same regardless of the diameter of pipe used. However, it doesn't seem right that, for example, a 20mm diameter pipe full of water and extending 5m above a 10m^3 tank would pressurise the tank to the same extent as pipe 2m in diameter filled (with a far greater weight of water) to the same height?
The cross-sectional area of the tube is small in comparison to the tank. My understanding is that the pressure in the tank would be the same regardless of the diameter of pipe used. However, it doesn't seem right that, for example, a 20mm diameter pipe full of water and extending 5m above a 10m^3 tank would pressurise the tank to the same extent as pipe 2m in diameter filled (with a far greater weight of water) to the same height?





RE: Water pressure in tank with open pipe
Mike Lambert
RE: Water pressure in tank with open pipe
Fundamentals of Hydraulics: Pressure
For a given depth, pressure is independent of the shape and size of the container (see below). This concept was first recognized by French scientist Blaise Pascal (1623– 1662).
RE: Water pressure in tank with open pipe
One thing you will need to be careful of is that with a small tube and large tank, the level of the water could change a lot based on only a small change of temperature. Hence a small increase in temperature could result in a higher level if the pipe is actually taller than 5m or less pressure if the water cools and the level in the pipe reduces.
You might be better off with a small header tank fitted with a ball valve and an overflow to maintain a constant level - think of a gravity fed central heating system.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Water pressure in tank with open pipe
RE: Water pressure in tank with open pipe
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Water pressure in tank with open pipe
What's throwing me off is that in usual problems, an object subjected to some water pressure is normally smaller in area than the cross-sectional area of the water above it (a diver in the sea, a submerged penstock in a river etc.
Thanks in advance.
RE: Water pressure in tank with open pipe
So in answer to your questions,
Will a fish experience a pressure equivalent to 5.5m of water head - Yes
Even though the X sectional area is different - Doesn't make any difference
Should the area be the same - No doesn't make any difference
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Water pressure in tank with open pipe
RE: Water pressure in tank with open pipe
The straw (pipe) will be too small for the fish to swim up, they will be introduced into the tank through sealed door.
RE: Water pressure in tank with open pipe
RE: Water pressure in tank with open pipe
RE: Water pressure in tank with open pipe
Stress is developed by resistance to deformation. Fluids exhibit shear strength when subject to deformation, so it is not always zero, as when the fluid is moving. Movement of fluids and semi-solids is resisted by its shear strength which of couse is described by viscosity. Semi-solids have a relatively high viscosity and can require signnificant force being applied to deform them, wile on the other hand the viscosities of air and water are relatively low and deform readily at low shear stresses.
RE: Water pressure in tank with open pipe
RE: Water pressure in tank with open pipe
Pressure is defined as force per unit area. It is usually more convenient to use pressure rather than force to describe the influences upon fluid behavior.
RE: Water pressure in tank with open pipe
It's not just the fish that will need to "acclimatise" I would assume that the dissolved gases content of the water increases as you increase the pressure (a quick Google search confirms this). Unlike in nature where the fish would be moving from lower pressure environment to a high pressure environment- here (I assume) you are changing the pressure of the environment.
By the way- 5m down isn't very far from the perspective of a fish.
As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"
RE: Water pressure in tank with open pipe
The fish are being passed through a 'fish friendly' turbine which operates at a maximum of 5m of water head, this is why we are acclimatising the fish to 5m in the lab set-up.