Industrial Exhaust Fan Types
Well, an industrial fan is a machine whose major and most important advantage is that it provides and accommodates a large flow of air or gas to many processes that happen in many different industries. This is done by rotating a number of blades that are connected to a hub and shaft and driven by a motor. A blower is the other name for a fan that functions where the resistance to the flow is primarily on the downstream side of the fan.
Most of the industrial fans may be categorized into one of two general types
- Centrifugal Fans
- Axial Fans.
Centrifugal fans are further divided into two categories that are:
- Forward curved centrifugal fans
- Backward curved centrifugal fans
Axial Fans
They are also known as propeller fans these kinds of fans generally move larger volumes of air at comparatively low pressures. Air enters and leaves the fan along the axis of the fan hub. These kinds of fans tend to vary from small applications such as cooling electronics to ventilating buildings and tunnels. The axial design uses axial forces to accomplish the movement of the air or gas, spinning a central hub with blades extending radially from its outer diameter. The fluid is moved analogously to the fan wheel’s shaft or axis of rotation. The axial fan wheel is often contained within a short section of cylindrical ductwork, to which inlet and outlet ducting can be connected. Axial fan types have fan wheels with diameters that usually range from less than a foot (0.3 meters) to over 30 feet (9 m), although axial cooling tower fan wheels may exceed 82 feet (25 m) in diameter.
In the broader vision, axial fans are used where the principal requirement is for a large volume of flow, and the centrifugal design where both flow and higher pressures are required. Axial usually supply framed axial fans, plate axial fans, cased axial fans, and EC high-efficiency axial fans available in standard or specialist specifications.
Centrifugal Fans
The centrifugal design uses the centrifugal force that is usually generated by a rotating disk, with blades that are mounted at right angles to the disk in order to impart movement to the air or gas and it also increases its air pressure very conveniently. The construction of the hub, disk, and blades is known as the fan wheel, and often includes other components with aerodynamic or structural functions. The centrifugal fan wheel is typically contained within a scroll-shaped fan housing. The air or gas inside the spinning fan is thrown off the outside of the wheel, to an outlet at the housing’s largest diameter. This at the same time draws more air or gas into the wheel through the central hole.
There are two main types of centrifugal fans:
Forward Curved Centrifugal Fans
Forward curved centrifugal fans are characterized by having some small blades which are curved in the direction of the rotation. This type of impeller draws most power at “free air” but speeds up as resistance is added and involves a scroll housing to operate efficiently. Air is discharged loosely, usually through a rectangular or circular discharge. The fans used in safety cabinets are large of this type. This develops high pressure fairly quietly, these fans are often used in ducted systems, also taking advantage of their directional delivery.
Backward Curved Centrifugal Fans
Backward curved centrifugal fans have relatively a lesser number of large blades which may be aerofoil sections, which usually curve away from the direction of rotation. Maximum power and minimum speed overlap at a point somewhere in the middle of the fan curve and as long as the motor is sized to operate at this point, the fan is said to have a “non-overloading characteristic”. The fan may be used with or without a scroll housing, giving great flexibility in system design. This type of fan involves a higher speed to generate pressure than forwarding curved fans of a similar size. Backward curved fans such as the new Wheel design are the most energy-efficient of all impeller designs and it is common that very large fan systems generally use backward curved fans for lower power consumption.
