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# High amp & pressure fan?

zoobie 09:54 12 Nov 2009
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I'm looking for a special high powered 120mm or 80mm axial 115AC fan that has high amps and pressure to force air thru cloth in an design experiment. Problem is, I can't find any. The highest amp fan I've found is only .26 amps. I see 12VDC fans all the time with high amps/pressure and can't figure out why I can't find the same in 115VAC. Is there a different formula used in AC vs DC? Where can I find 115VAC fans with high amps and pressure? I'm in the States. Thanks a lot

OTT_Buzzard 23:44 13 Nov 2009

It's not just to do with a chepo fan.

The load a fan draws is proportional to the speed at which it is running. Very roughly if you double the speed of a fan, you have to cube the original power requirement for the new fan speed.

Trying to remember back to fluid dynamics 1.01:

power = efficiency * blade area * 0.5 * air density * air velocity ^3

The faster it spins, the greater the mass of air that it has to move. Hence, if you had a 120mm fan that could draw several amps, it would be spinning so fast that you would end up with an airflow cavitation. This in turn would cause a random and variable loading on the fan blades from the airflow variations, which in turn would cause the power consumption to vary. That would lead to random and potentially very excessive torsional loads on the spindle.

That's why if massive volumes of fluids (including air) need to be moved, it is done using very large, slow spinning blades - think big ships and wind turbines.

woodchip 23:51 13 Nov 2009

On a Power Boat it would create Cavitation at the Propeller. in other words the water would get air bubbles round the prop and it would lose power

woodchip 23:53 13 Nov 2009

I have a Power Boat and Pitch of propeller as to be the right one for the Motor

OTT_Buzzard 23:54 13 Nov 2009

Exactly...and on, say, a submarine where the prop is permanently underwater you'd end up with vacuums forming in the water flow, reducing the efficiency of the prop to near 0.

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