Equalizing airflow through multi-hole orifices

  • I
  • Thread starter Anachronist
  • Start date
  • Tags
    Airflow
In summary, the Bernoulli equation does not make a distinction between one hole and multiple holes with the same total area, but in a practical implementation, the number of holes and the blade area can affect the flow and rotation speed of a turbine. The side with more holes and a higher blade surface area may experience more friction, resulting in a higher velocity and rotation speed. However, other factors such as pressure drop can also play a role in the observed differences.
  • #1
Anachronist
Gold Member
117
47
TL;DR Summary
One pressure vessel has 6 holes from which air escapes, another has 8 holes, total open area of the holes is same on each vessel. Should the volume flow be the same?
I know the Bernoulli equation for calculating the air velocity through a pressurized hole, but I am wondering if one hole of a given area behaves the same as multiple holes with the same total area. The Bernoulli equation doesn't make a distinction.

Background: As a personal 3D design and printing project I designed a siren whistle patterned after a Francis turbine, in which a dual runner (two runners back to back) chops the air coming out of exit holes on each side. The number of blades on each side of the runner is different (6 and 8) with a corresponding number of exit holes. As the runner rotates, the turbine produces two tones, with the airflow interrupted 6 times per rotation on one side, and 8 times per rotation on the other. The holes on each side have the same total open area.

The device works pretty well, but if I cover the holes on one side or the other, to allow only one side of the runner to drive its rotation, the rotation speed is clearly different for the same input pressure (by my best guess by breathing into it). It's slower when air exits only the 6-hole side.

That made me wonder if several small holes behave differently than fewer holes with the same open area.

Hmm, as I write this, I realize the difference could also be due to the different number of blades. The side with the higher number has a higher surface area on which the air can impart force.
 
Physics news on Phys.org
  • #2
To your summary question:

No - the flow shouldn't be the same. One of the factors controlling the flow is friction. The implementation with more holes has a higher 'perimeter/area' ratio. More 'perimeter' results in more friction. How much actual difference that makes depends on how large a factor friction is in your specific case - higher velocities result in more significant friction terms.
 
  • #3
That's what I thought. However, the effect I observe is the opposite of what would be expected (higher rotation when exhausting through the 8 hole side instead of the 6 hole side) so maybe the runner blade area is having a greater effect, which may be mitigated only slightly by the greater surface area of the holes.
 
  • #4
If you drive the turbine with a constant flow, then it may have greater pressure drop with the 8 hole side, which may explain the higher velocity.
 

1. What is equalizing airflow through multi-hole orifices?

Equalizing airflow through multi-hole orifices is a process used to distribute air evenly through multiple holes in a system. This helps to prevent uneven air pressure and flow, which can affect the performance and efficiency of the system.

2. Why is equalizing airflow important?

Equalizing airflow is important because it ensures that air is distributed evenly throughout a system, which helps to maintain consistent pressure and flow. This is crucial for the proper functioning of many systems, such as HVAC systems, engines, and pneumatic tools.

3. How does equalizing airflow through multi-hole orifices work?

Equalizing airflow through multi-hole orifices typically involves using a manifold or distribution block to evenly distribute air from a single source to multiple outlets. This can be achieved through various methods, such as using a series of valves or a network of interconnected tubes.

4. What are some common applications of equalizing airflow through multi-hole orifices?

Equalizing airflow through multi-hole orifices is commonly used in various industries, including automotive, aerospace, and manufacturing. It can be used in systems such as fuel injection, pneumatic tools, and hydraulic systems to ensure even distribution of air or fluid.

5. Are there any challenges or limitations to equalizing airflow through multi-hole orifices?

One potential challenge with equalizing airflow through multi-hole orifices is ensuring that all holes are of equal size and shape, as even small variations can affect the distribution of air. Additionally, the design and placement of the orifices can also impact the effectiveness of the equalizing process. Regular maintenance and calibration may be necessary to ensure optimal performance.

Similar threads

B Help understanding the physics of airflow
    • Classical Physics
Replies
3
Views
950
A few questions about airflow and filters...
    • Mechanical Engineering
Replies
5
Views
1K
I Graduation of air flow inside a vacuum chamber
    • Classical Physics
Replies
4
Views
1K
I Filling a pool with the hose end above or in the water
    • Classical Physics
Replies
10
Views
280
Pressure of water exiting a hole in PVC
    • Mechanical Engineering
Replies
12
Views
2K
I Why do bullets precess in the opposite way from gyroscope diagrams?
    • Classical Physics
Replies
23
Views
975
Underground pump vault airflow considerations
    • Mechanical Engineering
Replies
15
Views
813
Are Two Fans Better Than One?
    • Mechanical Engineering
Replies
6
Views
438
B What sound frequencies can pass through a hole in a wall?
    • Mechanics
Replies
31
Views
710
Car in corner -- relative airflow
    • Mechanics
Replies
20
Views
2K

Hot Threads

Recent Insights

Back
Top