1 fan & systems chris carr pe h. clay moore & associates rod furniss howden north america...
TRANSCRIPT
1
Fan & Systems
Chris Carr PEH. Clay Moore & Associates
Rod FurnissHowden North America
Key Account Manager - Nuclear
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• Pressure & Flow Definitions and Measurement• Development of Fan Curves• Performance of Various Blade Shapes• Fan Controls• System Effects
Aerodynamics3
4
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.
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AerodynamicsPressure & 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)
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AerodynamicsPressure & 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
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AerodynamicsPressure & 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
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AerodynamicsPressure & 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
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Fan Pressure Terms
• For a Given Fan, SPR is iiiAlways Greater Than FSP
• If the Specified Pressure is iiiAssumed to Be FSP, the Fan iiiSelected Will Be Smaller
AerodynamicsPressure & Flow Definitions and Measurement
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AerodynamicsPerformance of Various Blade Shapes
Common Blade Shapes
• Airfoil
• Backward Curved / Backward Inclined
• Radial / Radial Tip
• Forward Curved
• Axial
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Airfoil
• Highest Efficiency Centrifugal DDesign
• Limit Load HP Characteristic
• Low Noise
• Usually for Clean Applications
• Largest Diameter Centrifugal
• Highest Cost Centrifugal
AerodynamicsPerformance of Various Blade Shapes
Image area
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AerodynamicsPerformance of Various Blade Shapes
Image area
Backward Curved / Backward Inclined
• Essentially a Single TThickness Airfoil
• Efficiency slightly less than AAirfoil
• Limit Load HP Characteristic
• Low Noise
• For Clean or Dirty AApplications
• Lower Cost than Airfoil
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Radial / Radial Tip
• Lower Efficiency
• Continuously Rising HP .. CCharacteristic
• Higher Noise Levels
• May have Predominant BFP TTone
• Smaller Diameter
• Easily Armored for Erosive SService
• Lower Cost
AerodynamicsPerformance of Various Blade Shapes
Image area
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Forward Curved (SiroccoTM)
• Lower Efficiency
• Continuously Rising HP CCharacteristic
• Smallest Diameter Centrifugal
• Suited for High Volume/Low PPressure
• Distinctive Dip in P-V Curve
• Seldom Used Today
AerodynamicsPerformance of Various Blade Shapes
Image area
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Axial
• Airflow Parallel to Axis of RRotation
• High Efficiency
• Limit Load HP Characteristic
• Low Noise
• Suited for High Volume/Low PPressure
• Adjustable or Controllable Pitch
• Distinctive Dip in P-V Curve
• Controllable Pitch has Higher CCost
AerodynamicsPerformance of Various Blade Shapes
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AerodynamicsFan Controls
Fan Control
• Reasons for Providing Fan Control
• Methods of Control
• Efficiency Comparison
• Mechanical Arrangements
• Control Criteria
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AerodynamicsFan 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
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AerodynamicsFan Controls
Methods of Control
• None
• Outlet / System Damper
• Inlet Box Dampers
• Variable Inlet Vanes (VIV)
• Variable Speed
• Blade Pitch Control
• Combinations of the Above
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AerodynamicsFan Controls
Image area
Inlet Box Dampers
0
1
2
3
4
5
6
7
0 100 200 300 400 500 600 700 800
CFM
FSP - 0% IBD CLOSURE
HP - 0% IBD CLOSURE
FSP - 25% IBD CLOSURE
HP - 25% IBD CLOSURE
FSP - 50% IBD CLOSURE
HP - 50% IBD CLOSURE
FSP - 75% IBD CLOSURE
HP - 75% IBD CLOSURE
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AerodynamicsFan Controls
Image area
Variable Inlet Vanes
0
1
2
3
4
5
6
7
0 100 200 300 400 500 600 700 800
CFM
FSP - 0%VIV CLOSURE
HP - 0% VIV CLOSURE
FSP - 25% VIV CLOSURE
HP - 25% VIV CLOSURE
FSP - 50% VIV CLOSURE
HP - 50% VIV CLOSURE
FSP - 75% VIV CLOSURE
HP - 75% VIV CLOSURE
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AerodynamicsFan Controls
Image area
Variable Speed
0
1
2
3
4
5
6
7
0 100 200 300 400 500 600 700 800
CFM
FSP - 1180 RPM
HP - 1180 RPM
FSP - 880 RPM
HP - 880 RPM
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AerodynamicsFan Controls
Image area
Blade Pitch Control
0
1
2
3
4
5
6
7
0 100 200 300 400 500 600 700 800
CFM
FTP - BLADES OPEN
HP - BLADES OPEN
FTP - 25% BLADE CLOSURE
HP - 25% BLADE CLOSURE
FTP - 50% BLADE CLOSURE
HP - 50% BLADE CLOSURE
FTP - 75% BLADE CLOSURE
HP - 75% BLADE CLOSURE
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AerodynamicsFan Controls
Image area
Efficiency Comparison
0
20
40
60
80
100
120
30 40 50 60 70 80 90 100
% DESIGN FLOW
% D
ES
IGN
HP
OUTLET DAMPER
INLET BOX DAMPER
VARIABLE INLET VANE
VARIABLE PITCH
VARIABLE SPEED
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AerodynamicsFan Controls
Control Criteria
• Turndown / Leakage
• Sensitivity to Change / Stability / Transients
• Accuracy Required
• Repeatability
• Expected Efficiency
• Acoustic Considerations
• Structural Considerations