What is a centrifugal fan?
A centrifugal fan comes from the adjective ‘centrifugal’ which means to move away from the centre.
How do Centrifugal impeller Fans work?
As the centrifugal impeller fan moves air from its centre outwards and to the side, as in the word centrifuge, which, (taken from the Oxford English Dictionary) “Physics – The origin of which comes from the early 18th century from modern Latin ‘centrifugus’, from the Latin ‘centrum + fugus ‘fleeing’ (from fugere ‘flee’).
As the fan rotates, a pressure difference is built up on the impeller blades, this is because the impeller fan blades push air outwards, pushing the air outwards in a radial direction. On the concave of the impeller blade, a negative pressure is created as the fan rotates this draws air pressure into the space between the fan blades.
A centrifugal fan unit is usually driven by an electric motor. The motor spins the impeller, which draws air through its centre and outwards to the sides. The way in which it moves air to the side depends on the style of the impeller, of which there are 4 main types:-
- Multi-vane: (sometimes referred to as forward curved) which move large amounts of air at a low pressure, (High volume – Low pressure).
- Backward Curved: Which move high amounts of air at a medium to high pressure, (High volume – Medium pressure).
- Pressure: Which move medium amounts of air through at a high pressure, (Medium volume – High pressure).
- Paddle: Which move a large amount of air and more often particles and solids at a medium pressure (High volume – medium pressure… often solids)
How can you control centrifugal impeller fans?
You control a centrifugal fan by using a ‘damper’, which is a manual or electrically operated ‘flap’ that can be altered to restrict the airflow. The better and more common way of controlling a centrifugal fan unit is through a VFD or Variable Frequency Drive, which controls the frequency (Hz) supplied to the motor to increase or decrease the motor speed from its standard 50hz or 60hz.
It is also worth bearing in mind that backward curved and paddle fans, due to their characteristics, could overrun if the back pressure to the system isn’t enough. The inertia of an impeller being driven without the correct amount of restriction or back pressure could run away with itself, causing the motor that drives it to go faster than it should, which could increase the load on the motor causing it to go over its full load current and burn out. So it is imperative that the system is worked out accordingly.
What is the difference between Axial and (radial) Centrifugal fans?
Axial fans move air in only one direction, such as in a straight ducting or through a wall, and are used for basic applications such as roof extraction, extraction through a wall or low pressure ducting application (even though there are some higher pressure applications available).
Centrifugal fans offer a wider range of applications due to the amount of impeller types and typically send the air in a specific direction at any required angle.
Centrifugal Fan Wheels From Stock
Beatson supply centrifugal fan wheels across the UK 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 the UK 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).