Fan Velocity Pressure

Report
Fan & Systems
Chris Carr PE
H. Clay Moore & Associates
Rod Furniss
Howden North America
Key Account Manager - Nuclear
1
3
Aerodynamics
• Pressure & Flow Definitions and Measurement
• Development of Fan Curves
• Performance of Various Blade Shapes
• Fan Controls
• System Effects
2
HNA Profile
3
Aerodynamics
What is a Fan?
• Any device for producing a current of air by the movement
of a broad surface or a number of such surfaces.
4
Aerodynamics
Pressure & Flow Definitions and Measurement
Fan Flow Rate
• Often called inlet volume
• Measured at the fan inlet, by convention
• Measured in cubic feet per minute (cfm)
• May be converted to scfm (standard cubic feet per minute), or mass flow (lb/hr)
• Fan manufacturers commonly use acfm (actual cubic feet per minute)
5
Aerodynamics
Pressure & Flow Definitions and Measurement
Pressure
• Force per Unit Area
• Commonly measured in psi or inwg
Absolute Pressure
• Pressure when the datum is absolute zero
• iiAlways positive
Barometric Pressure
• Absolute pressure exerted by the atmosphere
• Always positive
Gauge Pressure
•
•
Pressure when the datum is barometric pressure
May be positive or negative
6
Aerodynamics
Pressure & Flow Definitions and Measurement
Static Pressure
•
•
Pressure due to degree of compression and density only
May be positive or negative
Velocity Pressure
• Pressure due to rate of motion and density only
• Always positive
Total Pressure
•
•
Algebraic sum of static and velocity pressures at a point
May be positive or negative
7
Aerodynamics
Pressure & Flow Definitions and Measurement
Fan Total Pressure
• Difference in Total Pressure between the fan outlet and fan inlet
• FTP = TPo - TPi
Fan Velocity Pressure
• Pressure corresponding to the average velocity at the fan outlet
• FVP = VPo
Fan Static Pressure
• Fan Total Pressure minus Fan Velocity Pressure
• FSP = SPo – TPi
Static Pressure Rise
• Difference in Static Pressure between the fan outlet and fan inlet
• SPR = SPo - SPi
8
Aerodynamics
Pressure & Flow Definitions and Measurement
Fan Pressure Terms
• For a Given Fan, SPR is
iiiAlways Greater Than FSP
Image area
• If the Specified Pressure is
iiiAssumed to Be FSP, the Fan
iiiSelected Will Be Smaller
9
Aerodynamics
Pressure & Flow Definitions and Measurement
Pitot – Static Tube
Image area
10
Aerodynamics
Pressure & Flow Definitions and Measurement
Fan Laboratory Test Setup
Image area
11
Aerodynamics
Development of Fan Curves
Fan Curve
Image area
12
Aerodynamics
Development of Fan Curves
System Curve
Image area
13
Aerodynamics
Development of Fan Curves
P-V and Peak Fan
Pressure
Image area
14
Aerodynamics
Development of Fan Curves
Selection Range
Image area
15
Aerodynamics
Performance of Various Blade Shapes
Common Blade Shapes
• Airfoil
• Backward Curved / Backward Inclined
• Radial / Radial Tip
• Forward Curved
• Axial
16
Aerodynamics
Performance of Various Blade Shapes
Airfoil
• Highest Efficiency Centrifugal
DDesign
•Limit Load HP Characteristic
Image area
•Low Noise
•Usually for Clean Applications
•Largest Diameter Centrifugal
•Highest Cost Centrifugal
17
Aerodynamics
Performance of Various Blade Shapes
Backward Curved /
Backward Inclined
• Essentially a Single
TThickness Airfoil
Image area
• Efficiency slightly less than
AAirfoil
• Limit Load HP Characteristic
• Low Noise
• For Clean or Dirty
AApplications
• Lower Cost than Airfoil
18
Aerodynamics
Performance of Various Blade Shapes
Radial / Radial Tip
• Lower Efficiency
• Continuously Rising HP ..
CCharacteristic
Image area
• Higher Noise Levels
• May have Predominant BFP
TTone
• Smaller Diameter
• Easily Armored for Erosive
SService
• Lower Cost
19
Aerodynamics
Performance of Various Blade Shapes
Forward Curved (Sirocco )
TM
• Lower Efficiency
• Continuously Rising HP
CCharacteristic
Image area
• Smallest Diameter Centrifugal
• Suited for High Volume/Low
PPressure
• Distinctive Dip in P-V Curve
• Seldom Used Today
20
Aerodynamics
Performance of Various Blade Shapes
Axial
• Airflow Parallel to Axis of
RRotation
• High Efficiency
• Limit Load HP Characteristic
Image area
• Low Noise
• Suited for High Volume/Low
PPressure
• Adjustable or Controllable Pitch
• Distinctive Dip in P-V Curve
• Controllable Pitch has Higher
CCost
21
Aerodynamics
Fan Controls
Fan Control
• Reasons for Providing Fan Control
• Methods of Control
• Efficiency Comparison
• Mechanical Arrangements
• Control Criteria
22
Aerodynamics
Fan Controls
Reasons for Providing Fan Control
• Uncertainty in System Calculations
• Safety Factor or Margin
• Expected Changes in the System with Time
• Normal Process Variations
• Provisions for Extraordinary Events
23
Aerodynamics
Fan Controls
System Pressure Loss
and Fan Design Pressure
Image area
24
Aerodynamics
Fan Controls
Moving the Operating
Point
Image area
25
Aerodynamics
Fan Controls
System Duty Cycle
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26
Aerodynamics
Fan Controls
Methods of Control
• None
• Outlet / System Damper
• Inlet Box Dampers
• Variable Inlet Vanes (VIV)
• Variable Speed
• Blade Pitch Control
• Combinations of the Above
27
Aerodynamics
Fan Controls
Outlet Damper / System
Damper
Image area
28
Aerodynamics
Discharge Damper
29
Aerodynamics
Fan Controls
Inlet Box Dampers
Image area
30
Aerodynamics
Fan Controls
Inlet Box Dampers
Image area
31
Aerodynamics
Fan Controls
Inlet Box Dampers
7
6
5
4
Image area
3
2
FSP - 0% IBD CLOSURE
HP - 0% IBD CLOSURE
FSP - 25% IBD CLOSURE
1
HP - 25% IBD CLOSURE
FSP - 50% IBD CLOSURE
0
0
100
200
300
400
CFM
500
600
700
800
HP - 50% IBD CLOSURE
FSP - 75% IBD CLOSURE
HP - 75% IBD CLOSURE
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33
IBD
Discharge
34
IBD
Discharge
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Aerodynamics
Fan Controls
Variable Inlet Vanes
Image area
36
Aerodynamics
Fan Controls
Physical Arrangement of
Cantilevered VIV
Image area
37
Aerodynamics
Fan Controls
Physical Arrangement of
Radial Vane Control
Image area
38
Aerodynamics
Fan Controls
VIV Fabrication
Image area
39
Aerodynamics
Fan Controls
Variable Inlet Vanes
7
6
5
Image area
4
FSP - 0%VIV CLOSURE
3
HP - 0% VIV CLOSURE
FSP - 25% VIV CLOSURE
HP - 25% VIV CLOSURE
2
FSP - 50% VIV CLOSURE
HP - 50% VIV CLOSURE
1
FSP - 75% VIV CLOSURE
HP - 75% VIV CLOSURE
0
0
100
200
300
400
500
600
700
800
CFM
40
Aerodynamics
Fan Controls
Variable Speed
7
6
5
4
Image area
3
2
FSP - 1180 RPM
1
HP - 1180 RPM
FSP - 880 RPM
HP - 880 RPM
0
0
100
200
300
400
500
600
700
800
CFM
41
Aerodynamics
Fan Controls
Variable Speed- VFD
and Gỳrol Fluid Drive
Rotating
Stall
42
Aerodynamics
Fan Controls
Blade Pitch Control
7
6
5
Image area
4
3
FTP - BLADES OPEN
HP - BLADES OPEN
2
FTP - 25% BLADE CLOSURE
HP - 25% BLADE CLOSURE
FTP - 50% BLADE CLOSURE
1
HP - 50% BLADE CLOSURE
FTP - 75% BLADE CLOSURE
0
HP - 75% BLADE CLOSURE
0
100
200
300
400
500
600
700
800
CFM
43
Aerodynamics
Fan Controls
Efficiency Comparison
120
100
% DESIGN HP
80
Image area
60
40
OUTLET DAMPER
INLET BOX DAMPER
VARIABLE INLET VANE
20
VARIABLE PITCH
VARIABLE SPEED
0
30
40
50
60
70
80
90
100
% DESIGN FLOW
44
Aerodynamics
Fan Controls
Physical Arrangement of
Various Control Devices
Image area
45
Aerodynamics
Fan Controls
Physical Arrangement of
Axial Blade Pitch Control
Image area
46
Aerodynamics
Fan Controls
Control Criteria
• Turndown / Leakage
• Sensitivity to Change / Stability / Transients
• Accuracy Required
• Repeatability
• Expected Efficiency
• Acoustic Considerations
• Structural Considerations
47
System Effects – Poor Flow
48
System Effects – Poor Flow
49
System Effects – Poor Flow
50
System Effects – Poor Flow
51
Fan & Systems
Chris Carr PE
H. Clay Moore & Associates
Rod Furniss
Howden North America
Key Account Manager - Nuclear
52

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