Fans are used in wide range of industrial applications ranging from power plant boilers , chemical processing industries and HVAC (Heating Ventilation and Air Conditioning) applications to move from one place to another. The fan size and power rating varies from few centimeter impeller diameter to several meters and power from few kW to MW depending on the application and air flow requirement. This presentation gives an introduction over view , types and applications of the Industrial Fans from the Fan Handbook Written by Frank.P.Bleier.

1. M A H E N D R A P R A B H U S U B R A M A N I
R O T A T I N G E Q U I P M E N T E N G I N E E R
FANS
FROM THE “FAN HAND BOOK” BY FRANK
P.BLEIER

2. B A S I C S O F S TAT I O N A RY A N D M O V I N G A I R
CHAPTER 1

3. BASICS OF STATIONARY AND MOVING
AIR
• Water vapor present in air reduces air density.
• Air density decreases with altitude .
• Positive and negative static pressure exist in moving air as well as
stationary air.
• A fan blowing into a system (including such resistances as ducts,
filters, dampers and heating or cooling coils) Produces positive static
pressure.
• A fan exhausting from a duct system produces negative static
pressure.
• Velocity pressure is the pressure we can feel when we hold our
hand in the air stream. It represents kinetic energy.
• Various degrees of turbulence – Slightly turbulent, Very Turbulent,
Extremely turbulent
• In Fans design Slightly turbulent and Very Turbulent are acceptable.

4. CONT.….
• Total pressure is TP defined as the sum of static pressure SP and
Velocity pressure VP;
• TP = SP + VP
• VP is always positive : TP and SP may be positive or negative.
• Air horse power (AHP) = 𝑄 ∗ 𝑇𝑃
Q – Flowrate , TP – Total Pressure
• Mechanical Efficiency (ME) or Total Efficiency (TE) =
𝐴𝐻𝑃
𝐵𝐻𝑃
• AHP - Air Horse Power (hp)
• BHP - Brake horse power (hp)
• SE - Static efficiency
• EE - Electrical efficiency
• SE - Set efficiency – 𝑀𝐸 ∗ 𝐸𝐸

5. CONT.….
• Air flowing through a converging cone reduces the
velocity pressure and increase the static pressure.
• The air velocity increases the static pressure will
decrease.
• Air flowing through a diverging cone reduces the static
pressure and increase the velocity pressure. It is called
static regain.

6. CHAPTER 2
AIRFOILS AND SINGLE T HICKNESS SHEET METAL
PROFILES

7. SHAPE OF TYPICAL AIRFOIL
Shape of typical airfoil

8. CONT..
• Positive pressure on the lower surface of airfoil
• Negative pressure on the upper surface of airfoil
• Combination of positive and negative pressure results in
a force F.
• Lift force L – Perpendicular to relative air velocity
• Drag force D – Parallel to relative air velocity

9. TYPES OF AIRFOIL
• Axial flow fans
• Concave side of airfoil is the
pressure side
• This is a normal condition
E.G Air plane wing

10. TYPE OF AIR FOIL
• Centrifugal fan with
backwardly curved planes
• Convex side of the airfoil is the
pressure side
• Helps broaden the range of
good efficiencies.

11. TYPE OF AIRFOIL
• Centrifugal fan with Radial tip
blades
• Concave side is the pressure
side
• This configuration is rarely
used
• High cost, handling dust laden
air , single thick blades

12. CHATER 3
T YPES OF FANS , T ERMINOLOGY AND MECHANICAL
CONSTRUCTION

13. AXIAL FLOW FANS
• Listed in the order of Increasing static pressure
1. Propeller fans
2. Tube Axial Fans
3. Vane Axial Fans
4. Two stage axial flow fans

14. PROPELLER FANS
• Also called as Panel fan
• Used to exhaust hot or contaminated air or corrosive gas
from factories, welding shops, foundries, furnace rooms,
laboratories, laundries or residential attics or windows.

15. TUBE AXIAL FANS
• Exhausting from Inlet duct
• Has cylindrical housing and fan wheel with a 33% hub tip
ratio and with 10 blades
• Blades may are may not have airfoil cross section
• Venturi inlet is required at inlet

16. VANE AXIAL FANS
• It has blades as well as guide vanes
• Used in blowing (outlet duct) and exhausting (inlet duct)
• Venturi inlet duct is required (due to air spin)

17. TWO STAGE AXIAL FANS
• Two fans in series
• Easy solution when higher static pressure are needed

18. CENTRIFUGAL FANS
• Listed in the order of decreasing efficiency
1. Centrifugal fans with airfoil blades
2. Centrifugal fans with backward curved blades
3. Centrifugal fans with backward inclined blades
4. Centrifugal fans with radial tip blades
5. Centrifugal fans with forward curved blades
6. Centrifugal fans with radial blades

19. CENTRIFUGAL FANS WITH AF BLADES
• Best mechanical efficiency and noise level (for
comparable tip speeds)

20. CENTRIFUGAL FANS WITH BACKWARD
CURVED BLADES
• Single thickness blades similar to AF blades
• Can handle contaminated air streams

21. CENTRIFUGAL FANS WITH BI BLADES
• Most economical in production
• Lower in structural strength and efficiency

22. CENTRIFUGAL FANS WITH RADIAL TIP
BLADES
• Only the blade tips are radial
• Used in high temperature and light concentration of
Solids.

23. CENTRIFUGAL FANS WITH FORWARD
CURVED BLADES
• Curved in the direction of rotation
• These fans are used in small furnaces, air conditioners
and electronic equipment whenever compact ness is
more important than efficiency.

24. CENTRIFUGAL FANS WITH RADIAL
BLADES
• Radial blades are rugged and self cleaning
• Handle corrosive fumes and abrasive materials

25. CONCLUSION
• Operating principle – Deflection of air flow and
centrifugal force.
• Axial fans – Deflection of air flow
• Centrifugal fans – Air flow deflection and Centrifugal
force
• Centrifugal fans produce more static pressure than axial
flow fans
• Centrifugal fans the airfoil lift contributes only a small
portion of pressure produced

26. CHAPTER 4
AXIAL FLOW FANS

27. NOMENCLATURE
• Axial flow fan indicates that the air flows through the fan
approximately axial direction.
• Centrifugal fans (sometimes called radial flow fans)
where the air flows through the fan wheel approximately
in a radially outward direction.

28. BLADE TWIST AND VELOCITY
DISTRIBUTION
• For good efficiency, axial air velocity should be same
from hub to tip

29. VANE AXIAL FAN DESIGN
• 𝐷 𝑚𝑖𝑛 = (19,000/rpm)* (sp)0.5
Dmin – Minimum hub diameter
Sp – Static pressure in wc (inches)
SP = 3.43 *10-9 * rpm * Zb* CL * l * W
Zb – Number of Blades
CL – Lift co-efficient
l – blade width at this radius
W – air velocity relative to the rotating blade

30. CONT.….
• Wheel Diameter 𝐷𝑚𝑖𝑛 = 𝑑2 + 61
𝑐𝑓𝑚
𝑟𝑝𝑚
0.5
• Inlet Bell will boost the flow rate by 10 to 15% and
increase the fan efficiency and reduce noise level
• Guide Vanes are used to eliminate the air spin past the
blades.
• Outlet guide vanes are preferred in most applications.

31. PROS AND CONS OF GUIDE VANES
• Vane axial fans to be used for higher pressure
requirements and higher efficiency
• The other disadvantages of inlet guide vanes
1) The shape of inlet vane is more critical for fan
performance
2) Noise level is high
3) Produces inlet turbulence
4) Deflection of air spin at inlet only in one point on
performance curve
5) Outlet vanes will provide more static regain

32. PERFORMANCE OF AXIAL FLOW FANS
(PRESSURE CURVE)
• Air movement and control association, Inc (AMCA)
• American Society of Heating , Refrigeration and Air
Conditioning Engineers, Inc (ASHRAE)
The depth of the stalling dip is
minor if the hup-tip ratio and
the blade angles are small.
For large hup-tip ratios and
larger blade angles, the
stalling dip becomes deeper.

33. PERFORMANCE CURVE

34. PRESSURE SAFETY MARGIN
• The maximum operating pressure of the selected unit
(i.e the peak pressure of the operating range) 30 to 50%
higher than the pressure required for the application to
avoid stalling
• If pressure safety margin is high it will increase the horse
power of the motor

35. INFLUENCE OF VARIOUS DESIGN
PARAMETERS
• Higher hup-tip ratio will increase static pressure
produced by Fan.
• Wider blade tip will increase static pressure of fan.
• Vane axial fans with larger hup-tip ratios have deeper
stalling dips.
• As the blade angle increases the volume flow increases,
Static pressure and stalling tip.

36. CONTINUATION
Affect of Increase in Tip Clearance on below parameters
Air Volume
Brake Horse power
Static pressure
Mechanical Efficiency

37. COMPARISON OF PERFORMANCE
CURVE

38. FACTORS PRODUCING NOISE
1. Operating in Stalling range
2. High tip speed
3. Lack of an inlet bell if installed without an inlet duct
4. Obstruction in the air stream ahead of and close to the blades
(Support arms, bel housing, conduit pipes)
5. Elbows in the duct work ahead and close to the fan inlet
6. Inlet guide vanes as opposed to the outlet guide vanes
7. Obstruction in the air stream past and close to the fan blades
8. Vibration due to poor balance or due to a resonance condition
9. Single thickness blades as opposed to airfoil blades
10. Many narrow blades as opposed to fewer and wider blades

39. OVER LAPPING PERFORMANCE
RANGES
• Static pressure is less than ¾” in WC – Propeller fan or
tube axial fan
• ½” to 3” in WC and should exhaust from duct – Tube
axial fan
• 1 ½” in WC and good efficiency is required – Vane Axial
fan
• Static pressure more than 6” WC – Two stage axial flow
fan (For better efficiency – Centrifugal fan)

40. COMPARISON BETWEEN VANE AXIAL
FAN VS CENTRIFUGAL FANS
Vane Axial Fan Centrifugal Fan
1. Greater Compactness
2. Lower First Cost
3. Straight-line Installation, Resulting
in a lower installation cost
4. Lower Sound Level at the same tip
speed
1.Natural adaptability to installations
requiring a 90° turn of the air stream
2.Better accessibility of the motor
compared with direct drive vane axial
fans
3.Better protection of the motor
against hot or contaminated gases
than for a vane axial fan with direct
drive
4.Greater assurance for operation in
the efficient and quiet performance
range, particularly for systems with
fluctuating flow resistance

41. CHAPTER 5
FAN LAWS

42. VARIATION IN FAN SPEED
• The air volume (cfm) varies directly with speed:
cfm2 / cfm1 = rpm2/rpm1
• The pressure vary as the square of the speed:
SP2/SP1 =(rpm2/rpm1)2
• The brake horse power varies as the cube of the speed:
bhp2/bhp1 =(rpm2/rpm1)3
• The Noise level is increased by 50 times the logarithm of
the speed ratio:
N2- N1= 50 log10 (rpm2/rpm1)

43. VARIATION IN FAN SIZE
• It is applicable for the fans with geometric proportionality
• Geometric proportionality means
1. Both fans have made same number of blades
2. Both fans have the same blade angle and any other
angles on the fan wheel and fan housing
3. If the diameters of the two fan wheels are D1 and D2,
for a size ratio D2/D1 , all other corresponding
dimensions of wheel and housing have the same ratio

44. CONT.….
• The air volume varies as the cube of the size:
cfm2 / cfm1 = (D2/D1 )3
• The pressure vary as the square of the size:
SP2/SP1 = (D2/D1)2
• The brake horse power varies as the cube of the speed:
bhp2/bhp1 =(D2/D1)5
• The Noise level is increased by 50 times the logarithm of the
speed ratio:
N2- N1= 50 log10 (D2/D1)

45. VARIATION IN DENSITY
• This law applies in following conditions
1. Fan operates at high altitude
2. Hot or cold air (density inversely proportional to the
absolute temperature)
3. Fan operates other than air
The air volume remains constant:
cfm2/ cfm1 =1
The pressures and brake horse power vary directly as the
density ρ:
SP2/SP1 = ρ2/ ρ1 = bhp2/bhp1
The efficiency and noise level remains constant

46. CHAPTER 6
SYSTEM RESISTANCE

47. SYSTEM RESISTANCE (BUBBLE POOL)

48. SYSTEM RESISTANCE (FILTER BAGS)

49. SYSTEM RESISTANCE (GRAIN BIN)

50. SYSTEM RESISTANCE (VENTILATING
SYSTEM)

51. SYSTEM RESISTANCE (VENTILATING
SYSTEM)

52. CONT.…

53. CONT.

54. CONT.

55. CONT.

56. CONT.

57. CONT.