AMETEK Aerospace and Defense
Technical Corner

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System Impedance

·          Laminar vs. Turbulent

·          Entrance/Exit losses

·          Velocity Head

·          Filtration

·          Push vs. Pull

·          Fan Obstruction

·          System Resistance/Fan Curve

·          Pressure Drop vs. Horsepower

Tech Corner - 2

Tech Corner - 3 

Calculating Flow Through A Nozzle

Tech Corner - 4 

Pressure vs. Suction – Advantages and Disadvantages


          Promotes heat transfer but distribution may be poor

          Air Leakage is outward keeping out dust (if filtered at fan)

          Fan handles coolest air which is more dense so mass flow is greatest

          Fan runs cooler- longer life

          Fan motor heat dissipates into cooling air stream



          Air distribution is more even

          Air Leakage is into enclosure, contaminating with dust

          Fan sees warmer air, delivering less mass flow due to lower density

          Higher temperature can reduce fan life

          Fan motor heat is not dissipated into cooling air stream