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Fan Problems & Solutions –

Aerodynamic

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• Surge • Inlet Box Vortex• Rotating Stall

Fan Problems and Solutions- Aerodynamic8

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Fan Problems & SolutionsAerodynamics

Poor Fan Performance

• Aerodynamically Induced Vibration in Fan Systems

• Pressure Pulsations

• Surge

• Inlet Box Vortex

• Inlet Cone Vortex

• Rotating Stall

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Fan Problems & SolutionsAerodynamics

Poor Fan Performance

Poor Fan Performance Includes But is not Limited to the Following:

• Incorrectly Selected Fan for a Given Duty

• Poor Installation, Casing Leakage.

• Incorrect Rotation of ILD & VIV.

• Erosion, Impeller, Casings and Inlet Cones

• Incorrect Rotor Rotation

• Poor Inlet Cone Lap & Gap

• Leaking Shaft Seals

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Surge

•. Surge is a Specific Type of Low iiiFlow Condition Which Creates an iiiAerodynamic Pulsation When a iiiFan Operates on the Positive iiiSlope Side of its Performance iiiCurve

• Problem is Associated with Flat iiiBladed Fans

Fan Problems and SolutionsAerodynamics

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Inlet Box Vortex

• Inlet Box Vortex Occurs in Fans iiiEquipped with Inlet Boxes iiiBecause of the Rapid iiiAcceleration of the Gas/Air iiiStream as it Changes Direction iiiFrom Radial to Axial, to Radial iiiand Then Tangential to the iiiImpeller

• Severity Increases with Flow

Fan Problems and SolutionsAerodynamics

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Fan Problems & SolutionsAerodynamics

Inlet Box and Inlet Cone Vortex• The Vortex is a Function of the Reynolds Number in the Inlet Box

• Gas/Air Velocity• Inlet Box Dimension• Kinematic Velocity

• Reducing the Reynolds Number Will Eliminate the Problem. This is Achieved by Installing a Splitter Plate in the Inlet Box, Which Changes The Inlet Box Dimension or Fins on Inlet Vane Blades.

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Rotating Stall

● Is Possibly the Most Severe and iiiDestructive Form of Pressure iiiPulsation

● Stall Occurs When the Angle of iiiAttack of the Air Flow Becomes iiiToo Severe. This Problem iiiOccurs When the Fan is iiiOperating on the Peak or iiiPositive Slope of the iiiPerformance Curve. Problem iiiMainly Associated with Airfoil and iiiBackward Inclined Fans

Fan Problems and SolutionsAerodynamics

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Stall Region

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Fan Problems & SolutionsAerodynamics

Rotating Stall

• Stall Cell Rotates in Opposite Direction of Rotor. Sets Up a Single Forcing Frequency at 2/3 or 4/3 Running Speed

• Rotating Stall in Axial Fans Causes High Cycle Fatigue of the Fan Blades and Catastrophic Failure

• Howden Uses Stall Warning and Detection Systems to Prevent the Fan from Operating in Stall

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Fan Problems & Solutions –

Aerodynamic