Fans Flashcards
1
Q
Axial-Flow fan defn
A
direction of airflow through the fan is parallel to the air or shaft of the fan
2
Q
Centrifugal/Radial-flow defn
A
the air enters parallel to the axis of the fan and is discharged radially
3
Q
Axial
A
- Normall ‘low’ pressure fans up to 3kPa or twin stage up to 6kPa
- Air volume up to 300m3/s
- Variable duty by changing
> blade angle
> number of blades
> number of fans
> Speed
4
Q
Centrifugal
A
- Normally ‘high’ pressure fans up to 7kPa
- Air volume up to 300m3/s
- Variable duty by changing
> speed
> Inlet guide
5
Q
Main fan compariston (axial)
A
- easy to install
- Cheap
- low pressure
- Bad stall characteristic
- Noise
6
Q
Main fan Comparison (centrifugal)
A
- Difficult to install
- Not cheap
- High Pressure
- Good stall characteristics
- Less noise
7
Q
Auxiliary (secondary) fan comparison
A
- Axial > easy to install > cheap > small > bad stall characteristics > Noise
- Centrifugal
> difficult to install
8
Q
Reversal of rotation
A
Axial
- reduce volume of air
- reduced fan pressure
- reversed airflow
Centrifugal
- Reduced volume of air
- Reduced fan pressure
- Continued airflow
9
Q
Fan performance curves
A
Must include
- fan speed
- air density
10
Q
Stall Zone
A
- Where the pressure and volume increase simultaneously
- Fan may enter this zone if the resistance of a system becomes excessive
- air separates from the blade surface causing excessive vibration
- Can cause catastrophic failure if allowed to continue
11
Q
Indications of Stall
A
- Fan vibration
- Unusual noises
- Motor current oscillates
- Volume and pressure fluctuates
12
Q
Stall Remedial Action
A
- Reduce pressure
> opening regulators
> opening doors
> Turn off other fans
13
Q
Fans in parallel
A
- Same pressure: identical fans provide double the air volume for the same pressure
14
Q
Fans in Series
A
Same air volume: identical fans provide double the pressure for the same volume
