Why does a fan seem to blow harder than it draws?

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SUMMARY

The discussion centers on the aerodynamics of fans, specifically addressing why a fan appears to blow harder than it draws air in. The key conclusion is that the design of the fan blades concentrates exhaust air into a constrained channel, resulting in higher velocity at the front. In contrast, the air intake comes from a larger volume, allowing the same mass of air to move at a lower velocity. This asymmetry in airflow dynamics explains the perceived difference in air movement.

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Shouldn't the end product of a system with such symmetry be more randomized than the initial?
 
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Loren Booda said:
Shouldn't the end product of a system with such symmetry be more randomized than the initial?

Aerrodynamics is a complicated subject! I believe the answer to your question is because the exhaust air has been concentrated into a fairly constrained channel by the shape of the fan's blades, at least close to the blades where you're most likely to put your hand to feel it. But the air being drawn in from the back of the fan comes from a much larger volume, and therefore the same mass of air can move with a lower velocity.

In short, the fan isn't a very symmetrical system.
 

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