A blower is a centrifugal fan, which is a mechanical device for moving air in a direction at an angle to the incoming fluid. Centrifugal fans would often contain a ducted housing to direct outgoing air in a special direction or across a heat sink. This type of fan is also called a blower fan, or squirrel cage fan. These fans increase the speed and volume of an air stream with the rotating impellers.
Blower fans utilize the kinetic energy of the impellers to increase the volume of the air stream. This in turn moves against the resistance caused by the ducts, dampers and other components as well. Blower fans displace air in radial direction, and change the direction by 90° of the airflow. This kind of stuff shall be sturdy, quiet, reliable, and capable of operating over a wide range of conditions. During the operation, blower fans are constant displacement or constant-volume devices. Therefore, at a constant fan speed, a blower fan moves a relatively constant volume of air rather than constant mass substances. This indicates that the air velocity in a system is fixed even if the mass flow rate through the fan is not. Because blower fans are not positive displacement devices, so the blower fans have certain advantages and disadvantages at hand. Things happen when blower fans are contrasted with positive displacement blowers. Since centrifugal fans are more efficient, whereas positive displacement blowers may have a lower capital cost to the buyers. So when purchasers are making their decision, they will have to estimate the projects and the expenses.
The shapes of centrifugal fan have a drum shape. This is composed of a number of fan blades mounted around a hub. And the hub turns on a driveshaft mounted in bearings in the fan housing. During the fan operation, the gas enters from the side of the fan wheel, and then it turns 90 degrees and accelerates. The acceleration is caused due to centrifugal force because it flows over the fan blades and exits the fan housing. Here the drum shapes and the fan housing a two key components and terms in the blower fan design. Only with well profiled outer shapes, the operation can be done as planned.
The primary components of a blower fans are five. They are fan housing, impellers, inlet and outlet ducts, drive shaft, and drive mechanism. These five main parts make the blower fan and make the rotation possible. Aside from these five key components, there are bearings, couplings, impeller locking device, fan discharge casing, shaft seal plates, and other smaller parts. Here we will also discuss about the bearing. Bearings are an important part of a fan in all kinds of variants. Sleeve ring oil bearings are used extensively in fans. Some sleeve ring bearings could be water cooled. This kind of sleeve bearings is often used when the fan moves hot gases. Heat is conducted through the shaft and into the oil, which must be cooled to prevent overheating the bearing. Lower speed fans have bearings in hard to reach points. Therefore, they use grease packed bearings. The drive mechanism of blower fans determines the speed of the fan wheel, and the extent to which this speed can be different.
There are two basic types of fan drive mechanisms. One is called direct, in which the fan wheel can be linked directly to the shaft of an electric motor. This shows that the fan wheel speed is identical to the rotational speed of the motor. With this type of fan drive mechanism, the fan speed cannot be varied unless the motor speed is adjustable. Furthermore, air conditioning will automatically provide faster speed because colder air is denser. Some electronics manufacturers have made blower fans with external rotor motors, and the rotor is directly mounted on the fan wheel. The other type is termed belt. Within this type of drive, a set of sheaves is mounted on the motor shaft, and the fan wheel shaft. A belt transmits the mechanical energy from the motor to the fan. The fan wheel speed is based on the ratio of the diameter of the motor sheave to the diameter of the fan wheel sheave.
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