Maximum Centrifugal Fan Outlet Velocity

[SAK9]

Most specifications inherited from grandfathers have an outlet velocity limitation of 10~12 m/s for centrifugal fans.Does anyone know what is the basis for this limit?Couldn't we use a higher out velocity (say 16 m/s )for fan selection?This may result in a smaller fan.An expansion fitting can be used to connect the fan to duct work and bring down it down to duct velocity(which could be around 10m/s).

Any thoughts???

 

[willard3]

Noise and pressure drop are higher at higher velocity......

 

[texanman]

as Willard3 indicated,... and also to get higher exit flow velocities you will need the fan to have higher RMP. This would lead to a whole set of other considerations in the design.

 

[marcoh]

Centrifugal fan selected for optimum efficiency usually have a discharge velocity of around 8m/s or less. The faster the discharge velocity, the smaller the fan (thus cheaper) but efficiency is reduced.

Therefore need to confirm if efficiency or cost is of greater importance to the project.

 

[macmet]

I have often been limited on my fan selections by speed as it keeps the noise levels down. This surprised me the first time I was asked but it has come up on a fairly regular basis.

 

[cry22]

"System effect" becomes very important if you use a discharge plenum, not much room for bad workmanship with high velocities.
Dynamic balancing of fans becomes even more important, a small wear of the fan shaft or small chip on a fan blade will result into a large imbalance and will create serious vibrations.

The slower, the better.