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| AIR FLOW DIRECTION IN CENTRIFUGAL FAN |
The principal parts of any fan are the impeller and the housing. Various other parts may be necessary or useful in the operation of the fan.
The impeller is the rotating element that transfers energy to the fluid. An impeller can also be called a wheel, a rotor, a squirrel cage, a propeller, or a runner. Impeller should probably be preferred as a general name, but wheel and rotor are also commonly used for all types. Squirrel cage is restricted to forward-curve centrifugals, and propeller is restricted to certain simple axials. Runner is used more frequently for pumps than for fans. The blades are the principal working surfaces of the impeller. A blade can also be called a vane, a paddle, a float, or a bucket. Vane should probably be preferred as a general name, but blade is also commonly used for all types. Paddle is usually restricted to an unshrouded type, and float to centrifugals in
general. Bucket is more frequently used for turbines than for fans. Shrouds may be used to support the blades. A shroud can also be called a cover, a disk, a rim, a flange, an inlet plate, a backplate, or a center plate. Shroud should probably be preferred as a general name, but cover and disk are also used. Flange, inlet plate, and rim are restricted to members that shroud the blades on the inlet side of a centrifugal fan. Back plate and center plate are restricted to members that shroud the side opposite the inlet on single-inlet
and double-inlet wheels, respectively. Hubs may be used to support the blades directly or through a shroud to the shaft. A hub can also be called a boss or a disk, but this terminology seems tobe disappearing.
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| SHROUDED IMPELLER (BACKWARD CURVED BLADE) |
The housing is the stationary element that guides the air or gas before andafter the impeller. A housing can also be called a casing, a stator, a scroll, a panel, a ring, or a volute. Housing, casing, and stator are all general. Scroll and volute are both restricted to centrifugal types, whereas panel and ring are restricted to propeller types. Centrifugal housing components include the side sheets and scroll sheets.
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| FAN CASING (VOLUTE SCROLL) |
The point of closest approach to the wheel is the cutoff, also called the tongue.The area over the cutoff is called the blast area.
