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Third Year > Fans > Flashcards

Fans Flashcards

1
Q

Converging

A
  • the conversion of static pressure to velocity pressure by gradually decreasing the cross-sectional area of a duct
  • static pressure decreases, velocity pressure increases - think about what’s happening back in the system and the pressure build up!
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2
Q

Static pressure

A

-the pressure air exerts on the inside of the duct walls or piping and is what overcomes the resistance of the ducts, fuels beds, filters and grates.

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3
Q

Velocity pressure

A
  • the pressure over and above static pressure

- caused by the impact of air flowing through a duct and is felt only by the surfaces that the air actually strikes

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4
Q

Total Pressure

A
  • simply adding static pressure to velocity pressure

- it will never change, but velocity pressure and static can alter

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5
Q

Purpose of fan casing

A

-to collect air leaving the impeller wheel and change the velocity head (velocity pressure) into pressure head (static pressure)

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6
Q

Axial flow fans

A

-propeller, tube axis, vane axis

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7
Q

Propeller fan

A
  • a unit that uses a propeller which is directly or indirectly driven
  • motor may rotate in both directions for reverse flow
  • very little pressure
  • used for air-cooled condensers, unit heaters, exhaust fans for ventilation
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8
Q

Tube axial fan

A
  • a heavier duty propeller fan that can be mounted as a unit within ducting
  • cause discharge air to swirl in the ducting, losing energy to friction
  • a channel (baffle) can be mounted on the discharge in order to cut down on the swirling
  • used for industrial, transportation, and marine where it can be loud
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9
Q

Vane axial fans

A
  • a tube axial fan equipped with outlet end guide vanes located behind the impeller.
  • the vanes eliminate most of the airflow swirl
  • guide vanes reduce internal friction and turbulence
  • overhead crawl spaces
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10
Q

Outlet damper controls

A

-

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11
Q

Variable inlet vane controls

A

-

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12
Q

Three styles of centrifugal fan blades

A

-straight radial, forward curved and backward inclined (most efficient because they use less HP)

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13
Q

Straight radial fan blade

A

-

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14
Q

Diverging

A
  • the conversion of velocity pressure to static pressure by increasing the cross-sectional are of a duct
  • velocity pressure decreases, static pressure increases
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15
Q

Forward curved fan blade

A

-

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16
Q

Backward Inclined

A

-

17
Q

Region of instability

A

-fan trying to find its sweet spot. While doing that it’s hunting and surging

18
Q

Cooling towers

A

-forced draft on the bottom, induced draft on the bottom

19
Q

Mechanical draft

A
  • induced draft (pulls air out) most service required
  • forced draft (pushes air in)
  • balanced draft (has both)
20
Q

Righting the curve

A

-

20
Q

Back pressure

A

-the static air

21
Q

Isolators

A

-

Third Year (21 decks)

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