Problem with parabolic flow profile in a tube
Problem with parabolic flow profile in a tube
(OP)
Hi smart people!
I am a chemist (doing a Ph.D in Analytical chemistry) and I pump plugs of chemicals through tubes (super fun!).
I would like to have a flat flow profile, not a parabolic one like I am having.
My question is this:
Is there a shape (of tube) where I can get a flat flow profile?
The liquid at the wall is traveling slower than in the middle. Should I make a conical "tube" to force the liquid at the wall to flow faster and catch up with the middle?
All help appreciated!
-H
I am a chemist (doing a Ph.D in Analytical chemistry) and I pump plugs of chemicals through tubes (super fun!).
I would like to have a flat flow profile, not a parabolic one like I am having.
My question is this:
Is there a shape (of tube) where I can get a flat flow profile?
The liquid at the wall is traveling slower than in the middle. Should I make a conical "tube" to force the liquid at the wall to flow faster and catch up with the middle?
All help appreciated!
-H





RE: Problem with parabolic flow profile in a tube
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Problem with parabolic flow profile in a tube
RE: Problem with parabolic flow profile in a tube
There is a Freon that's liquid at STP that can be used for the same purpose, and is heavy enough to make settling and recovery easy, and is of course almost incompressible.
In either case, because of contact with the wall as Zdas noted, there is a net toroidal flow within the bolus of interest. If that's a problem for you, you need to find a universe where the physics is different.
Mike Halloran
Pembroke Pines, FL, USA
RE: Problem with parabolic flow profile in a tube
Im working in the field of High Pressure Liquid Chromatography (HPLC) where our "tubes" are filled with semi-permiable particles and our plugs are parabolic. Changing the liquid is unfortuneltly not an option (sorry Compositepro). So what I understand from you is that I have no chance of changing the velocity distribution in the tube by going with another geometry (i.e conical)?
There is a closely related field where the flow is electroosmoticly driven. They have ionised liquid and charged wall surface (called Capillary Electrophoresis). They have "plug flow" due to the entire plug experiencing an electric field.
Perhaps my lack of knowledge in your domain is making it hard for me to correctly describe the problem. Apologies for that. I have attached a figure, my case on the bottom, the desired case on top.
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Thanks for the Galileo quote Mr. Simpson, Ill keep it in mind :)
MikeHalloran: I tried to ask my supervisor to change the fundamental rules of reality, but he said he did not have time this week :(
RE: Problem with parabolic flow profile in a tube
Otherwise, the only way to have a flat flow profile in normal fluid flow is to consider very high Reynold's numbers for short distances downstream from the entry.
RE: Problem with parabolic flow profile in a tube
RE: Problem with parabolic flow profile in a tube
Katmar Software - AioFlo Pipe Hydraulics
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Problem with parabolic flow profile in a tube
If so, you could place it between rigid plates, each having half a manifold on two parallel edges. Insert a sheet gasket on each face of the porous medium and clamp it tight, and you've got a pressure flow analog of electrophoresis.
Mike Halloran
Pembroke Pines, FL, USA
RE: Problem with parabolic flow profile in a tube
RE: Problem with parabolic flow profile in a tube
RE: Problem with parabolic flow profile in a tube
But if you want true plug flow, introduce plugs.
Is the reason for the question to produce discrete segments of different compositions in the same tube?
RE: Problem with parabolic flow profile in a tube
If the fluid is being pushed into a vacuum, then you'd have a chance if you can exactly predict the front "curve" of the fluid using a flat-surface plunger. Then make the recess to flatten-out the curve.