CAREER POINT UNIVERSITY

DHIRENDRA GOCHER(K10913) BTECH 3rd YEAR

6th sem

BRANCH-MECHANICAL

SUBMITTED TO - Mr. ADITYA MISHRA SIR

1

2

Fan Definition

What is a “fan”? “A fan is an air pump that creates a pressure difference and causes airflow. The impeller

does work on the air, imparting to it both static and kinetic energy, which vary in proportion, depending on the fan type.”

3

FansA fan is a constant volume machine. For a fixed speed, the fan will move the same volume of gas irregardless of gas density.

4

Types of Fan

Two basic types of fan are:

Centrifugal - rotating impeller to increase velocity of an airstream.

Axial - air is pressurized by the aerodynamic lift of the fan blade.

5

Centrifugal Fan Components

6

Axial Fan Components

7

Axial Fan Components

8

Centrifugal Fans - Blade Designs

Principles of operation The centrifugal fan uses the centrifugal power supplied from the

rotation of impellers to increase the kinetic energy of air/gases. When the impellers rotate, the gas particles near the impellers are thrown off from the impellers, then moves into the fan casing. As a result, the kinetic energy of gas is measured as pressure because of the system resistance offered by the casing and duct. The gas is then guided to the exit via outlet ducts. After the gas is thrown off, the gas pressure in the middle region of the impellers decreases. The gas from the impeller eye rushes in to normalize this. This cycle repeats and therefore the gas can be continuously transferred.

9

10

Centrifugal - Airfoil• Blade curves away from direction of

rotation• Highest efficiency• Relatively low noise• High structural strength• Power reaches max near peak

efficiency, then reduces twoards free delivery (self-limiting).

• For given duty, has highest speed of centrifugal design

11

Centrifugal - Backward Inclined• Efficiency slightly less than

airfoil design• Pronounced region of instability

where low efficiency and pulsations (stall, surge, bi-stable flow)

• Power reaches max near peak efficiency, then reduces t0wards free delivery (self-limiting).

• Consideration for use in applications where airfoil blade erosion concern

12

Centrifugal - Backward Curved• Power reduces towards free

delivery (self-limiting).• Promote smoother flow than BI

fan • Operate at higher speeds and

therefore require sturdier construction than FC

• Less susceptible to flow/fan instabilities due to less pronounced instability region

13

Centrifugal - RadialRugged blade design, self-cleaning• Lowest efficiency centrifugal• Used for material handling due to

blade strength• Moderate to high pressure industrial

applications• Power rises continually to free

delivery (overloading).

14

Centrifugal - Radial Tip

• Blade is radial at outer edge of wheel, curved in direction of flow as it moves inward

• More efficient than Radial blade• Used for mildly erosive environments• Higher pressure than Airfoil

15

Centrifugal - Forward Curved

Also called “Squirrel Cage”• Blade curved forward in direction of

rotation • Low pressure HVAC applications

(residential, etc.)• Lower speed than other centrifugals • Single thickness blade, lightweight

construction

16

Axial Fans - TypesPropeller - generally operate at

< 1/2 inch water gauge, inefficient, steeply rising power curve (overloading).

Tubeaxial - propeller mounted in cylindrical tube, ranges up to ~ 4 inches water gauge, overloading.

Vaneaxial - utilizes guide vanes to recover rotational energy, up to 10 inches (single stage), overloading.

17

Axial Fan - Guide VanesFunction - reduce the helical flow pattern of the fan.•Inlet - vanes guide airflow into a rotational pattern opposite to fan rotation to provide neutralize deflection by blades and result in axial flow

•Outlet - vanes take rotational pattern from blades and redirects it to an axial flow, converting some rotational velocity into static pressure.

18

AMCA ClassDefinition AMCA 99 - An established minimum performance level for fan aerodynamic performance in terms of pressure and airflow rate.

Simply put in general terms - the higher the Class, the greater mechanical strength (and price).

19

Centrifugal Fan Volume Control

Generally 3 methods:• Variable speed – changing fan speed results in a

change in fan flow.• Outlet damper – functions by changing system

resistance, forcing the fan to operate against higher backpressure and reducing the flow.

• Inlet damper – combination of resistance change and potential flow characterisitic change (spin, reduced turbulence) at fan inlet.

20

Centrifugal Fan VortexThe inlet box damper (positioned properly) and both types of inlet vane dampers pre-spin the air in the direction of fan rotation. By creating spin in the direction of fan rotation, the airflow, pressure and horsepower of the fan are reduced, resulting in a new fan performance curve.

21

References

•http://www.moorefans.com/•http://www.aaon.com/literature.aspx?id=1•http://www.chicagoblower.com/service/default.asp•http://www.cincinnatifan.com/catalogs/EngData-203-internet.pdf•http://www.northernblower.com/download/fanfacts.pdf•http://www.nyb.com/eng_letters.asp•http://www.greenheck.com/library/articles?c=2•http://www.hartzellfan.com/lib_pdf/Bulletin%20A-108-N.pdf•http://www.tcf.com/TCFBlower/literature.asp•http://www.howden.com/en/Library/HowThingsWork/•http://www.lorencook.com/PDFs/cookbook.pdf

22

THANK YOU