Flow

[mazamm]

We know that at the bottom of a certain tank/bottle the pressure of a fluid is high as compared to the top of the tank/bottle(assuming it to be open to atmosphere) according to the equation;
Pressure at bottom= density * 9.81 * height of tank

Then y does the fluid not go up to top of the tank/bottle since the fluid flows from high potential(pressure in this case) to lower potential??

 

[hydroman247]

The pressure is in equilibrium. The particle above particle a will be under 99.99999% the same pressure. Not enough pressure differential to move it above the other.

 

[hydtools]

That is why it is called hydrostatic and not hydrodynamic pressure. The weight of the fluid is sufficient to keep it in place and not flow.

Ted

 

[LittleInch]

Another way to think about this is conservation of energy. To move something higher requires energy to give it the potential energy it will have once it is at that higher level. The amount of energy required = density x 9.81 x height of tank, which exactly equals the pressure available at the bottom of the tank. Without extra energy, say a pump or extra pressure on top of the main tank, the fluid will not move.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[zdas04]

Yet another way to say it is "fluids flow from a state of higher total energy to lower total energy". Pressure is only one manifestation of energy. Height is another. For a fluid at rest with no external energy input, the pressure at the bottom of the column will exactly equal the energy of position at the top of the column resulting in no net flow.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[mazamm]

little inch

U talked about extra energy. If I give this energy in the form of heat, will the water from top go at the bottom ?
No. This would not happen I think. Infact the cold fluid will go up due to density difference

 

[zdas04]

"Cold fluid will go up due to density difference"?????????????? I'm seriously hoping that this is a language difficulty instead of an Engineering difficulty. Cold fluid is more dense than warm fluid. If you heat the bottom of a tank, the warm fluid will rise and the cool fluid will fall--gravity kind of demands it. If you chill the fluid in the top of a tank it will tend to fall which will displace the warmer fluid below towards the heat sink.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[mazamm]

zdas04

I meant to say that the hot fluid will go up due to density difference. (writing mistake)

I just meant to say that if heat is applied at the top, the energy level is increased but the fluid lets say water will evaoprate.

 

[automatic2]

the fluid with the least energy gravitates down. Only when their energy levels increase would they rise.

 

[crueltobekind]

well. the fluid at the top has higher potential energy than fluid on bottom. the fluid on the bottom does might have more pressure. but the energy, in terms of gravitational potential energy is less than fluid on the top.

E=mgh - the fluid on the bottom will have a lower height that fluid on the top, so it stands to reason that it will have lower potential energy. so if energy flows from higher state to lower state. fluid should be going from top to bottom. not bottom to top