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Roles of Impellers in Fans

4/16/2013 2:44:56 PM | by Anonymous

Impellers: Fan

An Impeller, which is found in fans, is a rotor, found inside a conduit or tube which is used to increase the flow or pressure of a fluid. In the case of turbines, an impeller is used to decrease the flow. Small propellers are similar to some impellers but without the large blades. Impellers are found in centrifugal and mechanical fans. Amongst their other uses, impellers are found in water jets to power high speed boats. Impellers are able to spin at a much higher speed than propellers since impellers have no large blades to run. The water which is bound through the impeller is carried by the housing which in turn creates a water jet which actuates the water forward.

 

Impellers in Centrifugal fans

Impellers can be found in centrifugal fans. A centrifugal fan is a device which is mechanical and it is used for moving air or other gases. Some commonly used synonyms for centrifugal fans include “blower” and “squirrel cage fan” (as it resembles a hamster wheel). With the rotating impellers, these fans increase the speed of the air stream. A centrifugal fan utilizes the kinetic energy of the rotating blades or impellers in order to uphold the pressure of the gas or air stream which in turn moves them against the counteraction caused by dampers, ducts and other components. A centrifugal fan increases the speed of air radially changing the direction of airflow commonly by 90 degrees. Centrifugal fans are able to operate over a wide array of conditions, mainly attributed to them being sturdy, capable, reliable and quiet. It is one of the most widely used fans.

 

The main parts of a centrifugal fan are the fan housing, inlet and outlet ducts, drive shaft and drive mechanism. Other components which may be used include couplings, fan discharger casings, bearings, etc. The fan drive determines the speed of the impeller and to the extent to which this speed can vary. There are three main types of fan drives. They are: direct drive, belt drive and variable drive. In the direct drive, the impeller can be directly linked to the shaft of an electric motor. This means that the motor’s rotational speed is identical to the impeller speed. The belt drive is where a set of sheaves are horsed on the motor shaft and the impeller and the belt transmits the mechanical energy from the fan to the motor. The variable drive utilizes magnetic or hydraulic couplings between the impeller shaft and the motor shaft.

 

Impellers in mechanical fans

Impellers are also found in mechanical fans. A mechanical fan is a machine designed to create flow within a fluid which typically comes in the form of a gas, most commonly air. Such mechanical fans usually consist of a rotating arrangement of either blades or vanes which react while on air. In this case, the impeller is referred to as the rotating assembly of blades and hub. The blades are also known as rotors or runners. They are most commonly contained in forms of cases or houses. This in turn increases safety and directs airflow by preventing objects from contacting the fan blades.

 

There are wide assortments of mechanical revolving blade fans. In homes fans can be found on floors or tables, hung from the ceilings, or are built into windows, walls or roofs. There are three main types of such fans which are designed to move air: axial-flow, centrifugal or cross flow. Axial-flow fans have impellers which subject air to move parallel to the shaft about which the blades rotate. A centrifugal fan’s impeller rotates which causes the air to enter the fan situated close to the shaft. The cross flow fan uses an impeller with forward curved blades and placed in a housing which consists of a vortex and rear wall.

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