Calculating Air Flow Within a Pipe

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Discussion Overview

The discussion revolves around the airflow dynamics within a pipe that can change shape at one end, specifically when suction is applied. Participants explore how the pressure gradient and airflow characteristics vary as the inlet hole enlarges, and the potential influence of centrifugal forces on the airflow, including the possibility of vortex formation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant describes a scenario where a pipe has a malleable end that can adopt a conical shape, questioning how the pressure gradient varies with the size of the hole when suction is applied.
  • Another participant suggests that the scenario resembles a horn.
  • A later post includes a diagram of the pipe's cross-section and reiterates the question about how airflow changes as the variable hole size increases.
  • One participant proposes that increasing the inlet size will reduce losses and increase flow rate, suggesting that maximum flow occurs when static pressure is fully converted to velocity pressure at the outlet.
  • It is noted that the static pressure starts at atmospheric and decreases through the cone, while velocity pressure increases, but one participant argues that there is no rotational component to suggest centrifugal forces or vortex formation.

Areas of Agreement / Disagreement

Participants express differing views on the effects of centrifugal forces and vortex formation, with some suggesting that these may not be relevant in this scenario. The discussion remains unresolved regarding the exact nature of airflow changes and the implications of the varying hole size.

Contextual Notes

There are assumptions about the behavior of airflow and pressure dynamics that are not fully explored, such as the specific conditions under which the suction is applied and the characteristics of the airflow at different points in the pipe.

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Consider a pipe. One end of it (hole) is malleable, in that we can make it larger so that the cylinder adopts a conical shape (yet the other 'hole' does not change).

If one were to apply suction at one end of the pipe, with respect to air flow, how does the pressure gradient vary within the pipe as the variable hole grows larger?

In what capacity will centrifugal forces act upon the air flow? (does this suggest a vortex?)
 
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Welcome to PF.

Could you provide a diagram please - it is very difficult to understand what you are trying to describe.
 
Seems like a horn.
 
Cross-section (pipe is solid & hollow).

[PLAIN]http://img138.imageshack.us/img138/5590/pipex.png

Assuming suction on the left end, how can we expect the airflow to change as x varies?
 
Last edited by a moderator:
Any ideas?
 
funbar said:
Cross-section (pipe is solid & hollow).

[PLAIN]http://img138.imageshack.us/img138/5590/pipex.png

Assuming suction on the left end, how can we expect the airflow to change as x varies?
Yes, as you increase the inlet and the size of most of the pipe, losses will drop so the flow rate will increase as x increases. The maximum flow rate is when the static pressure of the suction is all converted to velocity pressure at the outlet Y and other pressure losses are near zero.
If one were to apply suction at one end of the pipe, with respect to air flow, how does the pressure gradient vary within the pipe as the variable hole grows larger?
Through the pipe, you have an inlet velocity that gives you a certain velocity pressure at the inlet and static pressure is atmospheric pressure, then a linear static pressure gradient toward the outlet (suction end). Velocity pressure is constant throughout

Through the cone, the static pressure again starts at atmospheric and the velocity pressure is near zero, then the velocity pressure increases through the cone and static pressure decreases.
In what capacity will centrifugal forces act upon the air flow? (does this suggest a vortex?)
None that I can see - I don't see a rotational component here.
 
Last edited by a moderator:

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