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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

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HNA Profile

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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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Pitot – Static Tube

AerodynamicsPressure & Flow Definitions and Measurement

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Fan Laboratory Test Setup

AerodynamicsPressure & Flow Definitions and Measurement

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AerodynamicsDevelopment of Fan Curves

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Fan Curve

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AerodynamicsDevelopment of Fan Curves

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System Curve

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AerodynamicsDevelopment of Fan Curves

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P-V and Peak Fan Pressure

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AerodynamicsDevelopment of Fan Curves

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Selection Range

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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

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AerodynamicsPerformance of Various Blade Shapes

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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

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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

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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

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System Pressure Loss and Fan Design Pressure

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AerodynamicsFan Controls

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Moving the Operating Point

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AerodynamicsFan Controls

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System Duty Cycle

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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

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Outlet Damper / System Damper

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AerodynamicsDischarge Damper

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AerodynamicsFan Controls

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Inlet Box Dampers

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AerodynamicsFan Controls

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Inlet Box Dampers

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AerodynamicsFan Controls

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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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IBD

Discharge

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IBD

Discharge

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AerodynamicsFan Controls

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Variable Inlet Vanes

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AerodynamicsFan Controls

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Physical Arrangement of Cantilevered VIV

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AerodynamicsFan Controls

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Physical Arrangement of Radial Vane Control

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AerodynamicsFan Controls

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VIV Fabrication

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AerodynamicsFan Controls

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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

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Variable Speed

0

1

2

3

4

5

6

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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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Rotating

Stall

AerodynamicsFan Controls

Variable Speed- VFD

and Gỳrol Fluid Drive

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AerodynamicsFan Controls

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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

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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

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Physical Arrangement of Various Control Devices

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AerodynamicsFan Controls

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Physical Arrangement of Axial Blade Pitch Control

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AerodynamicsFan Controls

Control Criteria

• Turndown / Leakage

• Sensitivity to Change / Stability / Transients

• Accuracy Required

• Repeatability

• Expected Efficiency

• Acoustic Considerations

• Structural Considerations

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System Effects – Poor Flow

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System Effects – Poor Flow

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System Effects – Poor Flow

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System Effects – Poor Flow

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Fan & Systems

Chris Carr PEH. Clay Moore & Associates

Rod FurnissHowden North America

Key Account Manager - Nuclear