Air flow from large to small tube.What happens to pressure?

[pravi]

I would like to know what happens to air pressure when it flows from large tube to small tube. I would like to know the basic science behind this though I am pursuing my B.E. Moreover, does PV=mRT law apply here or some other principle applies here. What happens to temperature and other charactersitics. Please help me with this. Thanks.

 

[mfb]

I guess you are interested in https://en.wikipedia.org/wiki/Bernoulli's_principle]Bernoulli's[/PLAIN] principle.
pV=nRT is always valid in ideal gases in thermal equilibrium, that doesn't mean it has to be useful everywhere.

 

[SteamKing]

I would like to know what happens to air pressure when it flows from large tube to small tube. I would like to know the basic science behind this though I am pursuing my B.E. Moreover, does PV=mRT law apply here or some other principle applies here. What happens to temperature and other charactersitics. Please help me with this. Thanks.

You don't say what field your B.E. is in, but questions like this are covered in a course on fluid dynamics.

 

[rowny]

Best you can do is to use a fluid simulation software like Fluent or Comsol and see what happens yourself.

 

[russ_watters]

How much pressure? How big of a difference between tube sizes? Depending on the answer, this may be more of a thermodynamics question than a simple fluids flow question.

 

[boneh3ad]

Best you can do is to use a fluid simulation software like Fluent or Comsol and see what happens yourself.

Um, what? This problem is, in all likelihood, easily solvable analytically to within a very good approximation.

 

[rowny]

"Other characteristics" he says. For instance, the flow might be turbulent, meaning that velocity and pressure will oscillate in space. When the flow reaches a step-up/step-down obstacle (such as a different pipe), a vortex occurs at the edges. No analytical solution is possible for these.

 

[boneh3ad]

He also said "basic science" which implies turbulence and flow separation are probably not something to consider just yet.

 

[pravi]

I'm sad that Iam not able to find an answer

 

[BvU]

No need to be sad at all. You have to realize that your question is not extremely specific, so you get all kinds of answers. Can be frustrating or disappointing, but that's how it is in PF (and that's also what makes PF interesting for helpers, because they get all kinds of questions that appear easier or more difficult than intended ).

In fluid flow at a constriction the Bernoulli equation is a good start -- see Hyperphysics.

Next steps (e.g. http://www.nptel.ac.in/courses/112104118/lecture-14/14-7_losses_sudden_contract.htm) bring in more detail -- and as you see life isn't all that simple any more.

Up to you how deep you want to go; now you at least have a start and some useful search terms. Good hunting !

[edit] on the link mfb gave you, under the picture of an airplane wing, the 'accompanying' link makes clear that yes, the gas law applies and the temperature drops. A gas needs energy to expand (because that means it is doing mechanical work !); if it has to take care of that all by itself the temperature drops.

 

[sophiecentaur]

Best you can do is to use a fluid simulation software like Fluent or Comsol and see what happens yourself.

Simulation is the last resort when simple analysis gets bogged down with too much complexity. Simulations cannot give to any more than the answer to "what happens when I do this?" question when what you need is to know the relationship between variables.