Centrifugal Impellers
What is an impeller fan?
Impeller fans, also known as centrifugal fans or hamster wheel cages, are mechanical devices used to move air in a direction that is at an angle to the incoming source. Impeller fans are often connected to ducted housing which allows the air to be funnelled into a particular direction.
Sometimes known as ‘radial flow’ type fans, centrifugal fans can generate relatively high pressures and are better suited to high-pressure applications, compared to axial flow fans. Generally speaking, centrifugal fans are fitted with three types of blade:
- Forward blade
- Backward blade
- Radial blade
Centrifugal fans can vary in size considerably but are frequently used in material handling applications, in systems at higher temperatures and airstreams that contain high moisture and particulate content (informally known as ‘dirty’ airstreams). The smallest centrifugal fans can run on sub 125kW fans, whereas the largest can require hundreds of kW motors to drive them.
Backward curved bladed centrifugal fans have become more commonly used for air handling over the last 20 years. They are often more expensive than other types, as they are larger in size and also more complex in nature. This higher cost is balanced by their high efficiency, especially when compared to their forward-curved counterparts. Forward-curved impeller fans require scroll housing which contributes to their characteristically low noise level and small airflow.
How does an impeller fan work?
Impeller fans work largely due to positive pressure created by incoming air onto the convex side of the blades, this pushes the fan into motion which then leads to further force in the air. As the fan’s blades are pushed, air exits at an angle and negative pressure which draws more air into the fan and causes the fan to keep moving continuously.
How can you control centrifugal fans?
A variable inlet vane can be used to control airflow through a centrifugal fan that is otherwise fixed speed. These controls are external to the fan in order to maximise accessibility and give further flexibility in terms of mounting location. Variable inlet vanes alter fan performance by affecting the flow of gas before it enters the impeller.
When the vanes are fully open, they offer little to no resistance to incoming gas, which allows the fan to operate at maximum efficiency. As the vanes are closed, the air enters in the direction of the impeller’s rotation and reduces total pressure across the impeller, causing a reduction in power.
Two options of variable inlet fan are widely used, depending on the conditions that the fan is operating in and the damper size:
- Cantilever blades are typically used when dealing with high-temperature gas that contains corrosive or abrasive materials.
- Center hub supported blades, meanwhile, are used for cleaner air and moves air at a higher velocity.
Variable vane-controlled systems are extremely sensitive at lower loads, so even the smallest changes in angle can cause a large flow change, this is reversed when fans are subjected to higher loads. Unlike axial fan, variable vane controls are not linear.
What is the difference between axial and radial fans?
In the world of industrial fans, despite there being many names that they are referred by, there are predominantly two types of fan that are referred to as ‘industrial fans’: radial and axial fans.
When comparing a centrifugal and axial fan of the same flow and pressure, the main differences that set them apart are as follows:
- The axial fan will have a lower diameter impeller.
- The axial fan will have a higher dynamic pressure.
- The axial fan will operate at a higher speed.
- The centrifugal fan will have a slower peripheral speed than the axial fan.
- As the axial fan has a lower yield speed, it will have a higher power consumption.
- The axial fan will produce much more noise, but will be smaller, lighter and cheaper than the centrifugal fan.
The key information that most will focus on is the last point. Both axial and centrifugal fans are not made equal, however, as centrifugal fans are capable of withstanding more pressures of a certain amount than axial fans. As such, axial fans are much commonly found in low-pressure range environments, where their low weight, cost and general size is also a benefit. Axial fans are, by their nature, much simpler to install into a factory process, as the directly parallel nature of both suction and discharge nozzles can be connected seamlessly into a pipeline, whereas fitting a centrifugal fan requires more logistics to do so.
Why is it called a squirrel cage fan?
Squirrel cage fans, are sometimes known as centrifugal blowers; and take their common name from their similarity to a hamster wheel.
Why are impeller blades curved?
Impeller blades are curved in order to create both a convex and concave spaces which respectively create positive and negative pressure that creates the continuous motion that impeller fans are known for.
What is the difference between a blower and a fan?
There are a few major differences between impeller fans and blowers. Fans are electrical devices, whereas blowers are mechanical devices. Whilst fans circulate air around in every direction, blowers use impellers to channel air in one specific direction. Fans push air across along the axis of the rotor, whereas blowers use the centrifugal force created by the impeller fans to blow air in a specific direction. Fans are capable of moving large amounts of air at low pressures but do so at a specific pressure ratio of 1:1, whereas blowers move large columns of air at a ratio of 1:1-1:2.
Which is better blower or fan?
Blowers and fans are better at doing different jobs. Blowers excel at providing a powerful, direct airflow; meanwhile, fans are better at cooling a larger area and are also cheaper to run. Which is better for you will depend on your circumstances and needs.
Which type of fan gives more air?
The amount of air that a fan gives will depend on its blade size and the number of fan blades that it has. The wider or longer that you fans blade has the more airflow that will be capable of generating. It, therefore, follows that having more blades will also generate more airflow.
Centrifugal Fan Wheels From Stock
Beatson makes centrifugal fan wheels to any required specifications as well as having the 10-inch, 11-inch and 12-inch chip-shop fan wheels on the shelf. We can offer small aluminium impellers in various sizes as well as mild steel impellers from 150mm to 2000mm diameter. All these products come at very competitive prices.
All we need is the diameter, width and bore size as well as the direction of airflow. Our sales team can guide you through the requirements. We stock both single and double inlet fan wheels or backward curved. These are available in mild steel, stainless steel and alloy. Zinc and epoxy coating optional.
Get in touch with us with your required dimensions and specification, and we’ll get back to you with a competitive price. Alternatively, let us know about your needs and we can create a unit that will be right for you.
