Specific Speed Ns is a dimensionless ratio used to evaluate
airmover performance. Once the specific speed is
determined the type of airmover with the best efficiency
can be determined. Different types of airmovers operate
at peak efficiencies at different specific speeds.
Ns = (RPM · CFM 0.5 ) / SP 0.75
|
Specific Speed Range |
Most Efficient Type Airmover
|
| |
|
|
2K to 10K
|
High pressure vacuum |
|
6K to 20K |
Radial Wheel Blower
|
|
15K to 35K |
Tight Scroll Forward Curved Blower
|
|
25 to 40K |
Loose
Scroll
Forward
Curved Blower |
|
35K to 65K |
Backward
Curved or
Mixed Flow |
|
60K to 80K |
Mixed
Flow or Vane
Axial
|
