Today’s post comes from our manufacturer, M.K. Plastics’ blog, and it will explain the difference between the different type of fans they manufacture. Two general classifications of fans exist, centrifugal fans and axial flow fans. What sets them apart is how air passes through the wheel.
Axial Flow Fans
An axial flow wheel (called a propeller) propels the air in an axial direction with a swirling tangential motion created by the rotation of the blades. The rotation increases air velocity, producing velocity pressure and kinetic energy at very small increases in static pressure.
Axial flow fans come in many different variations, but they all have one thing in common: they rotate about a central axis and move a column of air parallel to this axis. In other words, the air enters from one direction, goes through the wheel, and continues out the other side in the same plane. They are commonly used in commercial applications. Fiberglass axial flow fans are finding greater adoption in industrial applications as an alternative to centrifugal equipment, which is more expensive.
Here are the three basic variations of axial flow fans, which all generally have the same performance characteristics.
Propeller fans are the most common type of fan and most of us are familiar with them. You’ve probably seen them in your office or home in the form of an air circulator fan. It could be a ceiling fan, a desk fan, or a pedestal fan. It has a propeller and it keeps you cool in warm weather. We use the same type of propeller fan, but it’s called an RFS panel or wall panel fan. has fiberglass housing and fiberglass propeller blades. It’s primarily used to vent out noxious gasses from chlorine storage rooms or wastewater treatment plants.
Tubeaxial fans have the same wheel design as propeller fans. However, they are mounted in a cylindrical tube or a duct and are often called duct fans. Tubeaxial fans employ a variety of propeller designs. They are designed for use with duct applications, and they are more versatile than panel fans by virtue of their construction. They are also more ductable for ventilation of industrial process.
Tubeaxial fans are able to handle up to four inches of static pressure, and low to high flows accommodate medium pressure. Wall panel fans, on the other hand, won’t see more than fractional static pressures because they’re not ducted.
Vaneaxial fans aren’t used as much as they were in the past. They are essentially the same as a tube axial fan, except they have vanes located on the discharge side of the impeller. The function of those vanes is basically to recover lost energy or rotation. Vaneaxial fans have mostly been replaced with more efficient centrifugal mixed flow fans.
Vaneaxial fans are normally duct mounted inside a building. You can also use them for ventilation. For example, when installed on a roof with a stack cap or damper, you can use them for general exhaust away from the inside of the building and up into the atmosphere.
Now let’s investigate the second type of fan/wheel, called a centrifugal fan, and take a look at how centrifugal fans are different from axial fans. First, air enters the impeller axially. Then the air is accelerated by the blades and discharged radially. In other words, the air goes in at the center of the wheel and then it goes out through the blades at90-degreeree angle. As the name suggests, centrifugal fans induce air by centrifugal force generated by the rotating column of air. This produces potential energy by the rotational velocities imparted to the air as it leaves the tips of the blades.
Centrifugal fans are the workhorse of the exhaust industry. Just like axial fans, there are different types of centrifugal wheels/fans. Here are all the basic types of centrifugal fans that you need to know about.
Forward Curved Fans
Forward curved fans/wheels, sometimes called volume or squirrel cage fans, use small and numerous impeller blades. They operate at relatively low speeds and pressures, which permits for lighter construction of the wheel, shaft, bearings, and housing.
Our equivalent would be the , which comes in a relatively small package. These fiberglass fans are used in many different applications, such as laboratory exhaust or ventilation in wastewater treatment plants. They deliver high, medium, and low volumes of air pressure no greater than 6 inches. They are normally selected at about 3 inches of water gauge or less.
Backward Incline Fans
Backward inclined fans, sometimes called load limiting or non-overloading fans, are the heavy duty centrifugal fan of the industry. They also come in a variety of different styles. The impeller blades tend to be larger and heavier than forward curved blades. They usually number anywhere between 8 and 12 blades.
Backward inclined fans are used to deliver medium to fairly high airflow, as their static pressure ranges all the way up to 20 inches of water gauge (and sometimes higher). There are three different categories of backward inclined wheels: flat single thickness, curved single thickness, and curved airfoil (which is most efficient).
Our equivalent fan for this type of application would be a . These can be used in heavy duty applications such as wastewater treatment plants, production facilities, silicon chip manufacturing plants, and semiconductor plants where they are pulling through scrubber systems with high restriction and static pressure.
Radial Blade Fans
Radial blade fans are generally smaller, narrower, deeper, and heavier than forward curved or backward inclined fans. The radial blade impeller usually comprises anywhere from 6 to 12 equally spaced flat blades. They’re generally simple in design, and they lend themselves to a more rugged construction.
Our equivalent of this type would be our . It’s designed primarily for low to medium airflows, but quite high static pressures up to 20 inches. This type of fan is often used in wastewater treatment plants and relatively low-flow, high-pressure applications.
To learn more, view the complete that M.K. Plastics offers. If you have any questions about using an axial, or centrifugal fan for your application, today, or visit our website. Remember you can always stay up-to-date on the latest industry happenings by following us on social media: Twitter, LinkedIn, Google+ and YouTube!
Nichole joined Flow Tech in 2013 as Director of Marketing. She leads our marketing communication initiatives including content marketing development, coordinating events and training, maintaining our digital presence and recruiting, as well as, some business development and office support. Nichole resides in Vernon with her husband Brian and son Roman. She enjoys hosting parties, cooking and lounging on the beach.