- Introduction
Fans and blowers provide air for ventilation and industrial process requirements. Fans generate a pressure to move air (or gases) against a resistance caused by ducts, dampers, or other components in a fan system. The fan rotor receives energy from a rotating shaft and transmits it to the air.
Difference between Fans, Blowers and Compressors
Fans, blowers and compressors are differentiated by the method used to move the air, and by the system pressure, they must operate against. As per American Society of Mechanical Engineers (ASME) the specific ratio – the ratio of the discharge pressure over the suction pressure – is used for defining the fans, blowers, and compressors (see Table 5.1).
5.2 Fan Types
Table 5.1 Differences Between Fans, Blower And Compressor
Equipment |
Specific Ratio |
Pressure rise (mmWg) |
Fans |
Up to 1.11 |
1136 |
Blowers |
1.11 to 1.20 |
1136 – 2066 |
Compressors |
more than 1.20 |
– |
Fan and blower selection depends on the volume flow rate, pressure, type of material handled, space limitations, and efficiency. Fan efficiencies differ from design to design and also by types. Typical ranges of fan efficiencies are given in Table 5.2.
Fans fall into two general categories: centrifugal flow and axial flow.
In centrifugal flow, airflow changes direction twice – once when entering and second when leaving (forward curved, backward curved or inclined, radial) (see Figure 5.1).
In axial flow, air enters and leaves the fan with no change in direction (propeller, tube axial, vane axial) (see below table).
Fan Efficiencies | |
Type of fan | Peak Efficiency
Range |
Centrifugal Fan | |
Airfoil, backward curved/inclined | 79-83 |
Modified radial | 72-79 |
Radial | 69-75 |
Pressure Blower | 58-68 |
Forward curved | 60-65 |
Axial fan | |
Vane axial | 78-85 |
Tubeaxial | 67-72 |
Propeller | 45-50 |