fluid moving

[peacefulheart]

Does fluid always move from high pressure to low pressure? Since pressure does not have direction, what dictates the direction of the flow? thanks a lot.

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[milski]

Does fluid always move from high pressure to low pressure? Since pressure does not have direction, what dictates the direction of the flow? thanks a lot.

Yes.

Statistics. Think about a wide door through which people are walking in both directions. If more people are walking out (compared to walking in), the total number of people outside will be increasing and people will "flow" outside.

The equivalent of people in the fluid situation is particles with higher energy.

 

[image187]

Does fluid always move from high pressure to low pressure? Since pressure does not have direction, what dictates the direction of the flow? thanks a lot.

I always try to picture a real-life situation because I find it helps to solidify the concept better. Take a car tire for instance. The outside air you drive through is 1 atm, and your car tire is 1 1 atm + approx 30-40 psi. When you drive over a nail and pop a hole in the tire, which way does the air move? Since I always end up on the side of the road, I know it always goes out. Double check on what the above poster said btw, I'm not sure but I don't think a smaller amt of air goes in than out, but I could be wrong. I always thought the fluid just moved from high to low pressure until an equilibrium was reached.

 

[peacefulheart]

I always try to picture a real-life situation because I find it helps to solidify the concept better. Take a car tire for instance. The outside air you drive through is 1 atm, and your car tire is 1 1 atm + approx 30-40 psi. When you drive over a nail and pop a hole in the tire, which way does the air move? Since I always end up on the side of the road, I know it always goes out. Double check on what the above poster said btw, I'm not sure but I don't think a smaller amt of air goes in than out, but I could be wrong. I always thought the fluid just moved from high to low pressure until an equilibrium was reached.

1. Thanks for the explanation .

2." Notice from the tube of flow that fluid does not necessarily move from high pressure
to low pressure. Pressure has no direction. The driving force behind the direction of fluid flow is the fluid's tendency to find its greatest entropy." (EK book)

thanks

 

[milski]

1. Thanks for the explanation .

2." Notice from the tube of flow that fluid does not necessarily move from high pressure
to low pressure. Pressure has no direction. The driving force behind the direction of fluid flow is the fluid's tendency to find its greatest entropy." (EK book)

thanks

That's actually a good point - all that I've said is applicable to a fluid with uniform consistency. If you have solutions with different concentrations separated by a filter permeable to only some of the particles in the solution, you can have a fluid move against the pressure gradient.

 

[image187]

That's actually a good point - all that I've said is applicable to a fluid with uniform consistency. If you have solutions with different concentrations separated by a filter permeable to only some of the particles in the solution, you can have a fluid move against the pressure gradient.

Oops, didn't even consider semipermeable membranes here. Yes, and a good example of this is in the capillary membrane (semipermeable), across which the direction of fluid movement is determined by "starling forces" which take into account hydrostatic pressure and osmolarity. Along the capillary's length, fluid moves from the bloodstream out into tissues on the arterial side due to hydrostatic pressure, and although the pressure is greater in the bloodstream on the venous side, a higher osmolarity drags fluid from the tissues into the capillary. In general though, considering only pressure and ignoring osmolarity or other things, I guess you could say that fluid tends to move from areas of greater pressure to areas of less pressure