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

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In summary, the end product of a system with symmetry may not be more randomized than the initial due to the shape of the fan's blades and the difference in velocity between the exhaust and incoming air. The fan is not a symmetrical system.
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Loren Booda
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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.
 

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

Fans are designed to circulate air in a room, creating a cooling effect. When a fan is blowing air towards you, it can feel stronger because it is directly hitting your body. However, when a fan is drawing air away from you, it may not feel as strong because the air is not being directly blown towards your body.

2. Is there a difference between the air flow in a fan when it is blowing versus when it is drawing?

Yes, there is a difference in the air flow when a fan is blowing versus when it is drawing. When a fan is blowing air, it creates a high pressure area in front of the fan and a low pressure area behind it. This difference in pressure helps to move the air in a specific direction. When a fan is drawing air, it is pulling air towards it and creating a low pressure area in front of the fan and a high pressure area behind it. This difference in pressure is not as effective in moving the air in a specific direction.

3. Why does a fan seem to blow harder when it is closer to an object?

When a fan is closer to an object, the air has less distance to travel before reaching the object. This means that the air is more concentrated and has a higher velocity, creating a stronger sensation of blowing. Additionally, when a fan is closer to an object, it can create a boundary layer of air around the object, making it feel like the fan is blowing harder.

4. Can the size or shape of a fan affect the way it blows and draws air?

Yes, the size and shape of a fan can affect the way it blows and draws air. A larger fan will generally create a stronger air flow, as it has a larger surface area to move air. The shape of the fan blades can also impact the air flow, as certain shapes may be more efficient at moving air than others.

5. Why does a fan seem to blow harder on a hot day?

On a hot day, the air in the room is warmer and less dense. When a fan blows air, it creates a cooling effect by moving the air around and creating a breeze. This can feel stronger on a hot day because the warm air is being replaced with cooler air, making the temperature feel more comfortable. In contrast, on a cool day, the air is denser and may not feel as strong when being moved by a fan.

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