Fans

Question 1

Converging

Answer 1

• 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!

Question 2

Static pressure

Answer 2

-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.

Question 3

Velocity pressure

Answer 3

• 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

Question 4

Total Pressure

Answer 4

• simply adding static pressure to velocity pressure

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

Question 5

Purpose of fan casing

Answer 5

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

Question 6

Axial flow fans

Answer 6

-propeller, tube axis, vane axis

Question 7

Propeller fan

Answer 7

• 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

Question 8

Tube axial fan

Answer 8

• 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

Question 9

Vane axial fans

Answer 9

• 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

Question 10

Outlet damper controls

Answer 10

-

Question 11

Variable inlet vane controls

Answer 11

-

Question 12

Three styles of centrifugal fan blades

Answer 12

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

Question 13

Straight radial fan blade

Answer 13

-

Question 14

Diverging

Answer 14

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

Question 15

Forward curved fan blade

Answer 15

-

Question 16

Backward Inclined

Answer 16

-

Question 17

Region of instability

Answer 17

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

Question 18

Cooling towers

Answer 18

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

Question 19

Mechanical draft

Answer 19

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

Question 20

Righting the curve

Answer 20

-

Question 20

Back pressure

Answer 20

-the static air

Question 21

Isolators

Answer 21

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