Can fluids flow naturally from areas of lower pressure to areas of higher pressure?

  • Thread starter klimatos
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  • #1
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Main Question or Discussion Point

I maintain that not only they can, but that observations illustrating the phenomena are common.

To keep the thread from fragmenting too badly, I should like to propose the following rules of discussion:

1) Liquids shall be limited to water and air.

2) Only natural flows may be offered. Nothing initiated, modified, or influenced by man or his works.

3) The flows must be unconstrained: no channels, pipes, or containers.

4) A flow from low pressure to high pressure shall be deemed to have occurred if the internal pressure (as measured by an imaginary manometer at the midpoint of the parcel of fluid) is higher at the finish of the flow than it was at the beginning.

5) Acceptable evidence shall consist of scientifically-accepted citations and/or compelling argument.

What are your thoughts?
 
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Answers and Replies

  • #2
olivermsun
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3) The flows must be unconstrained: no channels, pipes, or containers.
This one might be problematic. Are there unconstrained geophysical flows?
 
  • #3
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Well it really depends what you mean by 'pressure' in the fluid.

However in principle it's simple to offer examples where fluid flows from lower pressure to higher, simply by exploiting the gravity head component of Bernoulli's equation.

go well
 
  • #4
xts
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Any atmospheric or ocean circulation where air/water descends. Gulfstream sinking in arctic seas. Föhn winds. High pressure weather area.
 
  • #5
Bobbywhy
Gold Member
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I maintain that not only they can, but that observations illustrating the phenomena are common.

To keep the thread from fragmenting too badly, I should like to propose the following rules of discussion:

1) Liquids shall be limited to water and air.

2) Only natural flows may be offered. Nothing initiated, modified, or influenced by man or his works.

3) The flows must be unconstrained: no channels, pipes, or containers.

4) A flow from low pressure to high pressure shall be deemed to have occurred if the internal pressure (as measured by an imaginary manometer at the midpoint of the parcel of fluid) is higher at the finish of the flow than it was at the beginning.

5) Acceptable evidence shall consist of scientifically-accepted citations and/or compelling argument.

What are your thoughts?
As for 1): Did you mean FLUIDS shall be limited to water and air?
 
  • #6
rcgldr
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Assuming by flow you mean velocity, then due to momentum, this can happen. Pressure gradients only result in accelerations or declerations, not instantaneous changes in velocity.
 
  • #7
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As for 1): Did you mean FLUIDS shall be limited to water and air?
Of course, my stupid!
 
  • #8
411
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An excellent example of fluids flowing against the pressure gradient may be found in the field of limnology. In those parts of the world where lakes freeze over in the winter, the phenomena of spring and fall overturn occurs.

In the Fall, surface waters cool until the temperature of maximum water density occurs (about 3.94°C). At that time, portions of the surface water will sink through the underlying water until they reach the lake bottom. During that passage, the parcels of water move steadily against the pressure gradient. The pressure at the midpoint of the parcel when it reaches the bottom is substantially higher than when it started at the surface. Hence, there has been a natural flow of water against the pressure gradient.

This process repeats itself in the Spring.
 
  • #9
Simon Bridge
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Hang on a mo:
I maintain that not only they can, but that observations illustrating the phenomena are common.
...
What are your thoughts?
... what? Without supplying your own?
If your intention is to produce a discussion topic as in a social network, then isn't it more polite to start the ball rolling yourself with a bunch of your own examples instead of waiting until post #8?

An excellent example of fluids flowing against the pressure gradient may be found in the field of limnology. In those parts of the world where lakes freeze over in the winter, the phenomena of spring and fall overturn occurs.
... there is also a corresponding flow of water from the high-pressure zone to the low pressure one. This is a buoyancy effect - we'd normally think of it as the less dense water floats to the surface, dragging the more dense water down (to avoid a gap).

Cold air falls as hot air rises.
A water globule can fall from a tap into a full sink, and drop below the surface. Larger scale for waterfalls.
A big river flows into the sea - at the sea, part of the river water flows under the surface for a while. But that may not count as the water-center loses pressure.
A weighted bladder containing air is dropped into the sea and sinks ... the air is moving against the pressure gradient... but it's constrained isn't it?

I think you'll find that each time something flows naturally against the pressure gradient, something else has to go the other way.
 
  • #10
cjl
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Alternatively, any time the flow is slowing down, you'll tend to get an adverse pressure gradient.
 
  • #11
russ_watters
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You are certainly correct, Simon, but this thread definitely did not need to be resurrected. Locked.
 

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