What are the advantages of 3-bladed fans?

[magellan]

I've always wondered about this. I've noticed they have plenty of high CFM, high RPM models.

Is it also true that more fan blades = more static pressure?

 

[NiHaoMike]

They're more efficient in low static pressure applications.

 

[Bobnova]

If you think about fans as what they are, wings, it'll make sense. Wings only really work properly when they are in clean air. If the air they are working with is a chaotic mess, they don't work as well.
Three blade fans allow wide blades and also give some time between blades going through a given bit odd air space for the air to settle down a bit.
Turbulence is also loud.

What you lose with big gaps between the blades is pressure. Three blade fans have roughly no pressurizing ability.

 

[magellan]

Are three bladed fans also quieter for the CFM they deliver vs. 7 or 9 bladed fans?

So, basically 3-bladed fans make good exhaust or intake fans, but aren't good for
heatsinks or radiators?

 

[Silver_Pharaoh]

Are three bladed fans also quieter for the CFM they deliver vs. 7 or 9 bladed fans?

So, basically 3-bladed fans make good exhaust or intake fans, but aren't good for
heatsinks or radiators?

That's pretty much what I'm thinking.

But I think the 7 or 9 blade fans would be quieter than the 3 blade fans even if they [7 or 9 blade fans] have to spin faster to get the same CFM.

 

[freeagent]

Those high speed tri blades are good at removing any extra meat that you may have on your knuckle/appendage

 

[Bobnova]

Typically they're a bit quieter, but also typically they're high RPM, so it doesn't really matter from a practical perspective.

 

[magellan]

Typically they're a bit quieter, but also typically they're high RPM, so it doesn't really matter from a practical perspective.

So what's the point of manufacturing them at all? Do they at least use less power for a given CFM than a 7-blade or 9-blade fan?

 

[ATMINSIDE]

So what's the point of manufacturing them at all? Do they at least use less power for a given CFM than a 7-blade or 9-blade fan?

Because they move more air for a low pressure application.

 

[EarthDog]

For example, we have these in the top of our server racks. AC powered, lop off meat if you touch them speeds, to help move warm air out of the racks.

 

[NiHaoMike]

AC motors (driven direct off the mains) have a lower maximum power density than BLDC motors since an AC motor is limited to 3600 RPM at 60Hz. What the HVAC industry calls an ECM motor is actually a high voltage BLDC motor.

You'll find that 3 and 4 blade fans are very common in HVAC condensing units and ductless indoor units.

 

[magellan]

AC motors (driven direct off the mains) have a lower maximum power density than BLDC motors since an AC motor is limited to 3600 RPM at 60Hz. What the HVAC industry calls an ECM motor is actually a high voltage BLDC motor.

You'll find that 3 and 4 blade fans are very common in HVAC condensing units and ductless indoor units.

I have noticed that, ceiling fans, room fans all seem to be 4-bladed or 3-bladed.

Why don't ever make muffin fans of say, 4-blades or 8-blades?

Last question, are 3-bladed fans usually only made in 38mm or greater thicknesses?

 

[NiHaoMike]

Most applications for smaller fans need more static pressure than 3 or 4 blades can provide.