Chapter 127 Flashcards
List five different devices used to distribute the air of an air conditioning system
ducts, grilles, diffusers, dampers and louvres
The energy imparted to the air by a fan is in the form of what energy?
potential
With what device can you measure potential energy created by fans?
manometers
What are the three pressures created by a fan?
static, velocity and total pressure
How can static pressure be measured?
connecting the manometer at right angles to the duct
________ is caused by the impact of air flowing through a duct; it is felt only by the surfaces the air actually strikes
velocity
By connecting one end of the manometer at right angles to the duct wall and the other end with opening facing the air flow what pressure is being measured?
velocity
What happens to the pressures when the air goes through a converging section?
velocity pressure increases, static pressure decreases, total pressure stays the same.
What happens to the pressures when the air goes through a divergying section?
velocity pressure decreases, static pressures increases, total pressure stays the same
What are the two general groups of fans?
Centrifugal and axial flow
The air flows axially through the impeller
Axial flow fan
the air flows radially through the impeller
Centrifugal fan
What are the standard classes of air?
21 degrees celsius, 101.3 kPa, 1.2 kg/m^3
Four types of centrifugal fans:
Straight, backward inclined blades, forward curved blades, backward inclined airfoil blades
Three types of Axial fans:
Propeller fan, Tube axial fan, Vane Axial fan
These are normally used on smaller sized air moving equipment
Direct drives
These are used on most air conditioning, heating and ventilation applications
V-Belt Drives
Control of the static pressure and horsepower requirements at a given speed is obtained by using:
Variable inlet vane control
In order to convert static pressure to velocity pressure in an air distribution system it is necessary to:
decrease the cross-sectional area of duct
The propeller axial fan is used for:
high capacity, low pressure applications
Has low rotation speed:
forward curve
Coupling guards are used on?
direct drives
Has higher losses in ducts than the centrifugal fan
axial flow fan
Mostly used for high capacity, high pressure application
backward inclined airfoil fans
Velocity pressure is converted into static pressure in a centrifugal fan with use of an?
Volute shape
