# How does a ventilator work?

• PhyIsOhSoHard

#### PhyIsOhSoHard

I've been wondering about this for a while. Can somebody explain to me how a ventilator like this:

Works? Does it create gage pressures? When it starts rotating its blades, does that create a gage pressure above or below the atmospheric pressure? I'm a bit confused...

Last edited by a moderator:

Gauge pressures are just pressures referenced to atmospheric pressure, where gauge pressure of 0 is atmospheric pressure.

Technically, the machine in the image is called a 'fan'.

http://en.wikipedia.org/wiki/Mechanical_fan

1 person
Air is accelerated and decreased in pressure as it approaches the fan from behind, then as it crosses the "plane" of the rotating fan, it's pressure increases to above ambient, but there isn't much change in speed. The air then continues to accelerate and decrease in pressure until it's pressure returns to ambient.

The total mechanical energy of the air (pressure x volume, kinetic) is increased as it crosses the "plane" of the rotating fan.

Archived link to NASA article (NASA website is down due to USA shutdown):

propanl.htm

1 person
Air is accelerated and decreased in pressure as it approaches the fan from behind, then as it crosses the "plane" of the rotating fan, it's pressure increases to above ambient, but there isn't much change in speed. The air then continues to accelerate and decrease in pressure until it's pressure returns to ambient.

The total mechanical energy of the air (pressure x volume, kinetic) is increased as it crosses the "plane" of the rotating fan.

Archived link to NASA article (NASA website is down due to USA shutdown):

propanl.htm

Thank you!

How come you are happy with this? If I wouldn't know how a fan works, I still wouldn't know after checking these links. The NASA one gives me the impression it is circular !?

Maybe I'm too naive, but I think I can learn more if I find out how wings can generate lift when moving forward. For a fan, movement is in a circle; same difference. And the moving forward is relative wrt the air, because a fan has a footstand. Wouldn't work without friction...