Fans Flashcards
What is a pitot tube used for?
Measuring velocity
In ducting air flow what is Converging and Diverging?
Converging is when the area of the duct is decreased converting static pressure to velocity
Diverging the exact opposite
Conversion of static pressure to velocity pressure is done by
Decreasing Converging the area
Converting velocity pressure to static pressure is done by
Increasing the cross sectional area of a duct. - Diverging.
Arcing of static electricity Ina bearing causes what!?
Causes a rough bearing. Leading to bearing failure
When airflow deceases so does system pressure (back pressure) this cyclic behaviour is known as
Hunting or Surge
(Sounds like fan is breathing) most pronounced in Axial fans
Name the three general types of axial flow fans
Tube axial
Vane axial
Propeller
Centrifugal fans consist of what components
Rotating element
Scroll (casing)
Pedestal
Large single auction fans generally use what type of bearing?
Double row spherical roller bearing.
High velocity pressure energy of air is converted to static pressure with in
The scroll
Scroll is a Volute shaped collection chamber
Three types of mechanical draft
Induced
Forced draft
Balanced draft
What is the difference between forced air and induced.
Forced is pushing air,
Induced is a a negative pressure below atmospheric pressure
Advantages of mechanical draft
Increased efficiency of combustion
Independent of chimney temperate
Independent of atmospheric temperature
Can be regulated
What fan blades are most efficient
Airfoil style - capable of exceeding efficiency of up to 85%
Uses less HP
What blades have the highest velocity
Forward curved
What are the two types of cooling towers?
Atmospheric (using natural draft)
Mechanical
- forced draft
- induced draft
Fan shafts are supported by bearings in two locations, the fan wheel can be mounted how?
The fan wheel can be mounted In between bearings or mounted in an overhung co figuration
Fan inlet end may have louvers for volume control, the method of controlling the output of radial flow fans is called…
Suction throttling
Note: Outlet damper control is least efficient
What type of fan pulls hot hot combustion gasses out of a boiler.
Induced fans
Require more maintenance than forced draft fans because of abrasives and fly ash
What is the purpose of the scroll fan designe
Same as the Volute, creates velocity pressure and changes it into static pressure
What blade fans are used where high speed requires a strong wheel construction and high pressure services
Radial blade fans
What radial blade is ideal for hand eking material
Open wheel radial blade
