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Fan Selection Basics

Fan Selection Basics. Fan Selection Basics. 4. • Centrifugal Fan Selection • Fan Laws Specific Speed • Multiple Fan Arrangements Fan Features and Considerations. Fan Selection Basics. Centrifugal Fan Selection. Centrifugal Fan

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Fan Selection Basics

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  1. Fan Selection Basics

  2. Fan Selection Basics 4 • • Centrifugal Fan Selection • • Fan Laws • Specific Speed • • Multiple Fan Arrangements • Fan Features and Considerations

  3. Fan Selection Basics Centrifugal Fan Selection Centrifugal Fan • Air Enters the Impeller Axially, iiiThen Passes Through the iiiImpeller Radially • The Blades Drag the Air in a iiiCircular Motion and Centrifugal iiiForces Accelerate the Airflow iiiRadially Outward • The Airflow is Then Collected in iiiThe Volute Casing and iiiDischarged at Right Angles to iiithe Inlet Flow Image area ______ >

  4. Fan Selection Basics Centrifugal Fan Selection Motion of Air • The Increase of Centrifugal iiiForce With Radius Produces a iiiPressure Gradient, Whereby the iiiStatic Pressure in the Blade iiiIncreases With Radius • The Blades Drag the Air in a iiiCircular Motion and Centrifugal iiiForces Accelerate the Airflow iiiRadially Outward Image area

  5. Fan Selection Basics Centrifugal Fan Selection Motion of Impeller • The Motion of the Rotating iiiBlades Adds Rotational iiiMomentum to the Flow, iiiIncreasing the Velocity of Flow iiiin the Tangential Direction • As the Air Moves Radially iiiThrough the Impeller, the iiiAbsolute Velocity of the Flow iiiWill Increase, With the Absolute iiiMaximum Velocity at the iiiImpeller Outlet • The Increase in the Absolute iiiVelocity of the Air Leads to an iiiIncrease in the Kinetic Energy iiiand Dynamic Pressure Across iiithe Impeller Image area

  6. Fan Selection Basics Centrifugal Fan Selection Air Flow Through The Casing • A Proportion of the Dynamic iiiPressure From the Air Leaving iiithe Impeller is Transferred Into iiiMore Useful Static Pressure • The Fan Casing is Usually iiiVolute Shaped, Allowing iiiDiffusion of the Air Leaving the iiiImpeller to Take Place Image area

  7. Fan Selection Basics Fan Laws “The Fan Laws” It is not practical to test every fan at every variable which may be encountered. Fortunately, by use of a series of equations, commonly referred to as the “Fan Laws” it is possible to predict with good accuracy the performance of a fan at other variables. The variables include : Fan Size – D Fan Speed – N Fan Air Density - Fan Flow Rate - Fan Total Pressure - Fan Velocity Pressure – Fan Static Pressure – Fan Input Power – Fan Total Efficiency – Fan Static Efficiency – Compressibility Coefficient – Sound Power Level -

  8. Fan Selection Basics Fan Laws - Volume

  9. Fan Selection Basics Fan Laws - Pressure

  10. Fan Selection Basics Fan Laws - Power

  11. Fan Selection Basics Fan Laws - Summary Fan Law Summary

  12. Fan Selection Basics Fan Laws - Example

  13. Fan Selection Basics Fan Laws - Example

  14. Fan Selection Basics Specific Speed Fan Specific Speed • The Ability of a Fan To Generate iiiPressure and Flow With Impeller iiiSpeed. It is the Speed at Which a iiiFan of Indeterminate Diameter iiiWill Run at to Produce Unit Flow iiiat Unit Pressure • Low Specific Speed Fans iiiProduce High Pressures at Low iiiFlow Volume • High Specific Speed Fans iiiProduce Lower Pressures at High iiiFlow Volumes • Specific Speed is Proportional to iiiImpeller Inlet Diameter and iiiImpeller Width for a Given (Fixed) iiiWheel Diameter Image area ______ > Low Specific Speed High Specific Speed

  15. Fan Selection Basics Impeller Styles and Specific Speed Impeller Ranges Image area Radial Impeller Curved plate blades Radial Impeller Curved plate blades Radial Impeller Airfoil blades Axial Impellers, various hub sizes Airfoil blades

  16. Fan Selection Basics Multiple Fan Arrangements Multiple Fan Arrangements • Fans in Series • Fans in Parallel • Start Up in Series or Parrallel

  17. Fan Selection Basics Multiple Fan Arrangements Fans in Series Image area

  18. Fan Selection Basics Multiple Fan Arrangements Fans in Parallel Image area

  19. Fan Selection Basis Multiple Fan Arrangements Start Up for Fans in Series Image area

  20. Fan Selection Basics Multiple Fan Arrangements Start Up for Fans in Parallel Image area

  21. Fan Selection Basics Fan Features and Considerations Fan Features and Considerations Image area

  22. Fan Selection Basics Fan Features and Considerations Fan Features and Considerations Image area

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