How Fans Move Air: Propeller vs. Blade Shape

  • Context: High School 
  • Thread starter Thread starter bnvbnv
  • Start date Start date
  • Tags Tags
    Air Fan
Click For Summary

Discussion Overview

The discussion revolves around the mechanics of how fans and propellers move air, focusing on the differences in blade shape and the resulting airflow patterns. Participants explore the principles of pressure differentials and the effects of blade angles on air movement.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that fan blades create pressure differences, with higher pressure on one side and lower pressure on the other, which causes air to move.
  • One participant questions the reasoning behind air movement, noting that if blades create high pressure closer to the fan, it seems counterintuitive for air to flow towards the fan.
  • Another participant explains that while there is an outward flow, the majority of the air moves forward due to the design of the blades, which captures and directs the air flow.
  • It is noted that the angle of the blades significantly influences the direction of airflow, with a less than perpendicular angle promoting forward movement rather than outward flow.
  • Some participants mention that air has inertia, which prevents it from immediately reversing direction when passing through the fan.

Areas of Agreement / Disagreement

Participants express differing views on the mechanics of airflow and the implications of pressure differentials. There is no consensus on the reasoning behind the observed airflow patterns, and the discussion remains unresolved.

Contextual Notes

Participants reference the behavior of air in different environments, such as enclosed spaces, which may affect airflow dynamics. The discussion includes assumptions about pressure and inertia that are not fully explored.

bnvbnv
Messages
5
Reaction score
0
If fan blades move in a circular way how is the air moving towards you (in front of fan) ?

Also propeller and fan have different shapes, does it mean they work different?
 
Physics news on Phys.org
They create pressure on one side and reduce pressure on the other. A difference is pressure is what causes air to move. The shape of the blade pushes air on one side, creating higher pressure. On the other side a void is left, creating low pressure.
 
Let's say u sit in front of a fan.
In a fan like that if I am not wrong it is moving in the right direction (clockwise). By the shape of blades I assume they create high pressure on a side closer to you but it would mean air would travel backward to a side further away from you (from high pressure to low pressure). I don't get it (or my reasoning is wrong).
http://www.mh-china.com/UploadFile/2006112014312518080.jpg
 
There is some outwards flow, but most of the flow will be forwards. There is an increase in pressure from behind the fan to in front of the fan, but the blades move fast enough to capture the air and force it to flow forwards instead of backwards despite the pressure jump. Behind the fan, the air accelerates towards the fan as it's pressure decreases below ambient. As the flow passes through the fan blades, the pressure increases above ambient, but the speed of the air right at the fan blades remains about the same. Then the air continues to accelerate as it's pressure decreases from above ambient back to ambient.

As to why the air flows forwards instead of outwards, it's because of the angle of the blades. If the angle of the blades was perpendicular to the direction of rotation, the flow would be outwards and not forwards, but the angle is much less than this, so the direction of the "pull" and the "push" from the blades is mostly forwards and somewhat circular and/or outwards.
 
Last edited:
Hi bnvbnv
welcome to the forums


By the shape of blades I assume they create high pressure on a side closer to you but it would mean air would travel backward to a side further away from you (from high pressure to low pressure). I don't get it (or my reasoning is wrong).


it can't trave back because of the air that is still getting pushed forward from behind it

instead it moves out into the lower pressure area where you are sitting :smile:

Dave
 
bnvbnv said:
it would mean air would travel backward to a side further away from you (from high pressure to low pressure).
Air has inertia so it cannot immediately turn around, when it passes the fan. In an enclosed room it does travel back, just not through the fan but around it.
 

Similar threads

High School Fan is pushing in the front and sucking from the back
  • · Replies 32 ·
2
Replies
32
Views
2K
Why Is Fan Suction/Intake So Weak Compared to Exhaust?
  • · Replies 30 ·
2
Replies
30
Views
3K
To circulate air, fan points in or fan points out?
  • · Replies 16 ·
Replies
16
Views
2K
Calculating the speed air comes out of a fan
  • · Replies 1 ·
Replies
1
Views
3K
Do Dual Fans Increase Radiator Efficiency More Than a Single Larger Fan?
  • · Replies 6 ·
Replies
6
Views
6K
Best airflow for mini ITX PC case
  • · Replies 4 ·
Replies
4
Views
5K
High School Determining Electron's Momentum and Position Simultaneously
  • · Replies 4 ·
Replies
4
Views
1K
I need a small fan to push a lot of air because my bigger fan is too loud
  • · Replies 10 ·
Replies
10
Views
4K
Would a Centrifugal Fan Be Better for Moving Air Through a Small Hose?
  • · Replies 4 ·
Replies
4
Views
4K
Find RPM of a fan by recording a video
  • · Replies 33 ·
2
Replies
33
Views
7K