types of fans

8/21/2019 Types of Fans

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Types of Fans

Presented by:

Prabhat KumarPraful kishor

Pragyan Kumar


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Purpose:

To supply the necessary static pressure to move air in a

ventilation or exhaust system.

It is a kind of pump which is used for pumping or

circulating the air through the entire duct system and the

conditioned space.

Types:

Centrifugal fans or Radial flow fans (home furnaces, hairdryers, vacuum cleaners)

Axial flow fans


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Centrifugal Fans

Characteristics are low flow rates and highpressures with flow perpendicular to blower axis

Construction types includes:a) Forward curved

b) Backward curved &

c) Radial.


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a) Forward curved

Blades curve towards the direction of rotation. Fans have low space requirements and low tip speeds.

Used against low to moderate static pressures.

Not recommended for dust or particulate that would adhere to

blades.


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b) Backward inclined

Blades are inclined opposite to the direction of fan rotation.

High fan efficiency and relatively low noise levels.

Blade shape is conducive to material buildup

A typical backward-curved centrifugal fan, where the blades curve inthe opposite direction than the one they rotate in


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c) Radial

Blades are in a radial direction from the hub.

Fan have medium tip speeds.

Radial blade shape resist material build up.

Can handle either clean or dirty air.


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Axial Fans

Axial fans are used for relatively high flow rates and low

pressures with flow parallel to the axis of fan.

They also have low power input.

They are generally selected for simple extraction or coolingapplications with very low system resistance, such as moving

air from one large space to another (i.e. from factory to

outside), desk fans and condenser cooling in refrigeration.


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Types


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Special Types of Fans


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Fan Selection

Various factors effecting fan selection are:

Volume required (cfm)

Fan static pressure

Type of material handled

Explosive or inflammable material

Direct driven vs belt driven

Space limitations

Noise

Operating temperature

Efficiency

Corrosive applications


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Fan SelectionConsiderations for fan selection are :

1. Capacity:

Flow rate based on system requirements. Expressed as actual cubic feet per

minute.

Pressure requirement based on system pressure requirements.

2. Air stream:

Material handled through fan. Small amount of smoke or dust - backward inclined centrifugal or axial

fan is selected.

Light dust fume or moisture - backward inclined or radial fan is preferred.

Heavy particulate loading - radial fan is selected.

Explosive or flammable material.

Spark resistant construction is used.

Explosion proof motor is used.


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Fan Selection

3. Physical Limitations:Fan size is determined by

Performance requirements

Inlet size and location

Fan weight

The most efficient fan size may not fit the physical space available.

4. Drive arrangements:

Electric motor is the power source of fans.

Unlike packaged fans, for larger units the motor is coupled

directly to the fan or indirectly by a belt drive.


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Fan Selection

Standard drive arrangements are: Direct drive:

Offers more compact assembly and assures constant fan speed. Fan speeds are limited to available motor speeds.

Belt drive: Offers flexibility in changing the fan speed.

Important in applications where changes in system capacity or pressurerequirements are needed.

5. Noise: Generated by turbulence within the fan housing. White noise which is a mixture of all frequencies is mostly produced.


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Fan Selection

6. Safety and accessories:

Safety guardsare required at inlet, outlet, shaft, drive and cleanout

doors.

Accessorieshelp in future maintenance requirements.

Flow control can be done using dampers.

Outlet dampers:

Mounted on the fan outlet.

Adds resistance to the system when partially closed.

Inlet dampers: Mounted on the fan inlet.

Pre-spins air into the impeller.

Lowers operating horsepower.


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Thank You

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types of fans

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