fans Flashcards
3 types of pressure from fans
static
velocity
total pressure
airflow through the system is controlled by this
damper
type of pressure that air exerts on the inside of duct walls
static
type of pressure measured at fan discharge with ducting 90 degrees
static
type of pressure caused by air flowing through a duct and is felt only by the surfaces that the air actually strikes
velocity
type of pressure measured by connecting one end of the manometer at right angles to the duct wall and the other end with the opening facing the airflow
velocity
pressure conversion static to velocity
decreasing cross sectional area
converging
pressure conversion velocity to static
increasing cross sectional area
diverging
mechanical draft type where pressure in the furnace is below atmospheric pressure.
Fan located between the boiler and the chimney
induced draft
centrifugal blade fan most effecient and require less horsepower
backward incline blade fan
centrifugal blade fan has a lower speed for the same volume, low speed good for hvac application
forward blade fan
centrifugal blade fan are used where high speed requires a stronger wheel
radial blade fan
centrifugal fan casing cause this pressure change
velocity of static
advantage of axial flow fans
low cost
compactness
axial fans should not be used in these system
ducted air distribution system
centrifugal or axial fans rotate at higher rpm for same air flow
axial
tube axial or vane axial has less airflow swirl
vane axial
another name for impellers on centrifugal fans
wheels
used on fans with constant speed motors and are the least expensive efficient control
outlet damper control
radial vanes installed on fan inlet. vane shaft interconnect so that all the vanes rotate open and closed in unison
variable inlet vane control
used on many centrifugal fans to muffle the loud inlet sound generated by the increased air velocity and air shock as it flows into the eye of the fan wheel
air inlet silencer
isolator absorb vibration and allow for large thermal movement
spring type
isolator more compact, less flexible and become hardened with age
rubber disk
isolator have large capacity to absorb vibration
oil type vibration
ground brush arrangement mounted on isolated fans to ground the static electricity generated while the fan is running
static arrest
cooling tower fan blade tip to housing ring clearance
1/2% of fan diameter
