Centrifugal Fan Types

There are several kinds of centrifugal fan wheels which are designed for variouscapacitiesand applications. The most common centrifugal fan types are Backward inclined, Radial, Forward curved, and radial tip. 

Lets start by reviewing backward inclined fans. Backward Inclined fans get their name from the blades’ backwardly inclined orientation, relative to the wheel’s rotation. These fans generate medium to high amounts of airflow, at low to medium amounts of pressure. Capable of efficiencies of 80-90%, backward inclined fans are the most energy-efficient of the centrifugal fan types. Some characteristics all backward inclined fans have in common are large inlet and outlet openings, relative to casing size and wide casings, relative to wheel width. In general, backward inclined fans are vulnerable to material in an airstream because material tends to build up on the back side of the blades, which can cause imbalance.  

There are 3 major backward inclined wheel types; airfoil, single thickness, and backward curved. 

Airfoil wheels are the most efficient backward inclined wheel design, but they’re only intended for use in clean, dry airstreams, unless special design considerations are made. The superior efficiency of these wheels is a result of their airfoil blade shape. The blades are either extruded or formed to make a profile known as an airfoil, which has a similar shape to an airplane wing. This leaves a hollow interior, making it susceptible to moisture buildup through condensation, and erosion by material impact. 

Single thickness wheels use flat blades that are much better suited to material and moisture laden applications than airfoil wheels, but this comes with the loss of some efficiency. While the solid blade design allows these wheels to handle moderate amounts of material and moisture, it’sslightly less efficient than the airfoil wheel due to the flat blade profile. 

The backward curved wheel is similar to the single thickness wheel. The solid, curved blades on these wheels provide comparable material and moisture handling ability as single thickness blades, while the curved blade shape allows for slightly different performance characteristics. 

Next, we’ll look at Radial fans. Radial fans get their name from the way the wheel’s blades are positioned radially to the hub. Radial bladed fans are designed to generate medium to high amounts of pressure, at low to medium amounts of airflow. These fans can be identified by their narrow casings, relative to wheel width, and their small inlet and outlet openings, relative to casing size. Because of the higher pressures and material handling ability many of these fans are designed for, Radial bladed fans are inherently less efficient than backward inclined fans, typically operating around 50-65% efficiency. There are several kinds of radial bladed wheels, used for different applications.

The paddle wheel is a common radial bladed wheel type. The wide, flat, radial bladeson a paddle wheel give a self-cleaning design, and makes them great for abrasive applications requiring high pressure.

The radial wheel has a few design variations outside of the paddle wheel. 

The shrouded paddlewheel uses the same paddle blade design, but adds shrouds to both sides of the wheel, which has multiple benefits. Adding shrouds to a paddle wheel’s blades helps hold the air on the blades, which results in about 10% added efficiency. The added rims also help stiffen the bladesmaking this paddle wheel variation common for higher pressures and speeds. 

The Radial Backplate wheel is another variation of the paddle wheel. This design adds robust gussets between the blades, making it the most rugged wheel design available. These wheels are used for the heaviest of material handling applications, but also make for an inefficient and loud fan design.

Another common centrifugal fan type is the Forward Curved Fan. The wheels in these fans use thin, forward curved blades that cup the air as the wheel rotates, allowing them to produce moderate to high amounts of airflow, at relatively slow speeds and low pressure.

The last centrifugal fan type is the radial tip fan. These wheels combine the blade profiles of backward inclined fans, and radial fans. While most of the blade length on these wheels sits at a backward incline, the tips of the blades change direction to a radial orientation. The blades on these wheels allow radial tip fans to fill in more intermediate operating conditions. 

To summarize, there are many fan designs available, and by understanding a system’s aerodynamic requirements and airstream composition, you can identify the best fan for your application.