Classification of Industrial Fans
1.- Definitions
2.- Fan Laws
3.- Classification of Fans

Turning machine that transmits energy to the fluid circulating inside it by increasing pressure.


Volumetric flow related to a certain air density.

Static Pressure: Air pressure caused by its degree of compression. It can be positive or negative. In the fan it is equivalent to the difference between the static outlet pressure and the total inlet pressure.
Dynamic Pressure:

Air pressure caused by movement. Dynamic pressure can only be positive. In the fan it is equivalent to the average of the speeds at the outlet.

Total Pressure:

Air pressure owing to compression and movement. It is the algebraic addition of the dynamic and static pressures at a certain point. Therefore, if the air is motionless, the total pressure equals the static pressure. In the fan, it is the difference between the total pressures determined at its outlet and inlet.

Fans Laws

If in a given system the air density is kept constant, a fan corresponds to:

- Q1 / Q2 = n1 / n2.
- pe1 / pe2 = (n1 / n2)2.
- hp1 / hp2 = (n1 / n2)3.
  - Q = Volume
- pe = Static Pressure
- hp= Absorbed power
- n= Rotation speed (rpm)

Fans Clasification

Fans are divided in two groups:




Wheel usually have two or more singlethickness blades in a single ring enclosure. Efficiencies are generally low and use is limited to low pressure. High volume air moving applications such as air circulacion within a space or ventilation trough a wall without attached duct work .


The wheel is similar to the propeller type excep it usually has more blades of a heavier increase efficiency and pressure capability.

Ducted HVAC applications where air distribution on the downstream side is not critical. Industrial applications include drying ovens, paint spray booths and fume exhaust systems.


Most efficient axial type fan. Uses straight- ening vanes to improve efficiency and pressure capability. Blades often often have airfoil shapes and may be available whith adjustable pitch. Pressure capabilities are medium to hight.

General HVAC systems especially where straight thru flow and compactness is required. Good downstream air distribution. Used in many industrial applications.
INLINE CENTRIFUGAL This type is actually a centrifugal fan, with airfoil o backward inclined wheel in a Vaneaxial Casing. Good efficiency but lower than a similar centrifugal type . Used primarily for low pressure return air systems in heathing, ventilating and air conditioning applications. Has straight thru flow.


They are those in which the flow of air changes its address, in an angle of 90°, between the entrance and exit. They are usually sub-classified, according to the form of the shovels or álabes of the rotor, in the following way:


The wells blades are small and curved forward in the direction of the wheels rotation. This fan runs at a relatively low speed to move a given amount of air. This wheel type is most often called a squirrel cage wheel. Primarily for low pressure hesting, ventilating and air conditioning such as domestic furnaces, central station units and packaged air conditioning equipment.

This weel is like a paddle wheel with or without side rims. The blades are perpendicular to the direccion of the wheels rotation and the fan runs at a relatively medium speed to move a given amount of air. The radial blade type is designed for material handling applications , features rugged construction and simple field repair . Also used for high pressure industrial requirements.


The wheels blades are flat and lean away from the direction of the wheels rotation . This fan runs at a relatively high speed to move a given amount of air. It is more efficient than the above listed types. General heating , ventilating and air conditioning systems. Used in many industrial applications where the airfoil blade might be subjected to erosion from light dust.

Although nota a "Basic Type", this is an important refinement of the Backward Inclined wheel design. It has the highest efficiency and runs at a slightly higher speed than the standard flat blade to move a given amount of air. Most efficient of all centrifugals. Usually used in both larger HVAC system and clean air industrial applications where the energy savings are significant. Can be made with special construction for dusty air.

The wheels blades are somewhat cupped in the direction of the wheels rotation but the blade lesns back so that its outside tip approaches a radial position. This fan runs at approximately the same speed as a backward inclined wheel to move a given amount of air. This type is also designed for material handling or dirty or eroside applications and is more efficient than the radial blade.
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