Why does air speed change in different sized tubes?

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    Air Speed Tube
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Discussion Overview

The discussion revolves around the behavior of air speed in tubes of varying diameters, particularly in the context of fluid dynamics principles such as the equation of continuity and pressure differences. Participants explore the implications of these principles in both theoretical and practical scenarios, including singing and fluid mechanics applications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants identify the equation of continuity as the principle governing air speed in tubes, stating that for a constant flow rate, air moves faster through smaller diameters due to the conservation of mass.
  • Others argue that air speed is influenced by pressure differences rather than solely by volumetric flow rates, suggesting that larger diameter pipes can exhibit higher velocities under certain pressure drop conditions.
  • A participant introduces a practical example involving blowing through a straw, discussing how factors like Reynolds Number and turbulence may affect the distance a fluid can travel when expelled.
  • There is a mention of the importance of airflow in singing, where constricted airflow can negatively impact sound quality, linking the discussion back to the principles of fluid dynamics.

Areas of Agreement / Disagreement

Participants express differing views on the primary factors influencing air speed in tubes, with some emphasizing the equation of continuity and others highlighting pressure differences. The discussion remains unresolved regarding the relative importance of these factors.

Contextual Notes

Participants do not fully agree on the assumptions regarding the conditions under which air speed changes, such as whether the fluid is incompressible or the specific effects of pressure drops in varying tube diameters.

DeBruyn
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Hello,
I was looking for the name of the principle which governs the following-

given a constant air flow- air moves faster through a tube with a smaller diameter than a tube with a larger diameter.

Wouldn't you like to know what this has to do with singing?


Thank you
Debruyn
 
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equation of continuity

DeBruyn said:
Hello,
I was looking for the name of the principle which governs the following-

given a constant air flow- air moves faster through a tube with a smaller diameter than a tube with a larger diameter.
The name of the principle is the equation of continuity (or the principle of mass conservation).

The conservation of mass leads, for an incompressible fluid, to the equation of continuity: the volume flow rate must be constant at all points in an air stream. The volume flow rate is given by Volume/time = Area x Speed. Thus, for a given flow rate, air will flow faster through a tube with smaller diameter.

Wouldn't you like to know what this has to do with singing?
Sure!
 
DeBruyn - Air speed in a tube is generally looked at as a phenomenon which is caused by a difference in pressure. It is not forced by some volumetric flow rate, though I suspect that's what you had in mind.

In fact, if you have a pressure drop in a given length of pipe, say a 100 foot long section of pipe and a 5 psi drop, the larger diameter pipe will have a significantly higher velocity, even though the pressure drop and length of pipe are the same.
 
Doc Al said:
The name of the principle is the equation of continuity (or the principle of mass conservation).

The conservation of mass leads, for an incompressible fluid, to the equation of continuity: the volume flow rate must be constant at all points in an air stream. The volume flow rate is given by Volume/time = Area x Speed. Thus, for a given flow rate, air will flow faster through a tube with smaller diameter.


Sure!


One of the main aims in classical singing is to keep the muscles of the neck relaxed thereby keeping the throat open and relaxed as opposed to constricted and tense. If a singer is not providing sufficient airflow- the body will automatically try to help out in the process by constricting the throat- thus concentrating the airflow in order to make more out of the airflow which is provided. This does not create a desirable sound! Providing the correct airflow is imperative for the most efficient tone.
Thank you for your help!
 
Blowing through a straw

So you get a pop and straw, fill up your mouth with pop (ready to blow at someone), and blow hard. The pop spews out then it is all gone and air follows. Can you maximize the distance the pop flies out? In fluid mechanics there is a factor called a Reynolds Number. It basically talks about the size of pipe and pressure will cause the fluid to glide across fluid easily, or become turbulent and begin spiraling. Taking also into account the fact that pop is still stuck in the straw and not fixed in one point, air that follows will be interrupted. The interruption will always be changing its shape and position, so how can you maximize it? If you can get the pop to become turbulent for a while to help build up pressure, can you then increase the velocity at which it comes out of the straw, and therefore add to the distance it flies?
 

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