New Fans

Question 1

What is the purpose of a fan?

Answer 1

Create a pressure difference that provides a change in air pressure that is usually intended to promote air movement through a duct system

Question 2

How are fans selected?

Answer 2

For certain applications depending upon it’s adequacies and inadequacies

Question 3

How to identify a centrifugal fan?

Answer 3

If airflow through the fan is perpendicular to the fan shaft

Question 4

How to identify an axial fan?

Answer 4

Airflow is parallel to the shaft

Question 5

3 types of axial fans?

Answer 5

Propeller, vane axial, tube axial

Question 6

Application of a propeller fan?

Answer 6

Factories, welding shop, foundries, furnace rooms, labs, laundries, HVAC condenser and evaporator fans

Question 7

6 operational characteristics of propeller fan?

Answer 7

Slower RPM, moderate temperatures, large volumes of air flow, low static, no ductwork, usually mounted onto an opening

Question 8

Why is tube axial more efficient than a propeller fan?

Answer 8

Higher speed and close tolerance allow tube axial to operate at higher static

Question 9

Greatest inefficiency of a tube axial fan?

Answer 9

Discharge air in spiral motion producing high duct system losses (turbulence)

Question 10

Design improvement that makes vane axial more efficient than tube axial?

Answer 10

Guide vanes. reduces turbulence and promotes laminar flow

Question 11

More efficient? Air foil blade or cross flow blade?

Answer 11

Air foil blade fan

Question 12

Centrifugal fans are constant displacement. What does that mean?

Answer 12

Move constant volume rather than constant mass

Question 13

List 4 kinds of backward inclined centrifugal fan blades

Answer 13

Airfoil, backward curved, backward inclined, radial tip

Question 14

How fast do we run a backward inclined fan blade?

Answer 14

Twice the speed of forward curved fan

Question 15

How much static can a backward inclined fan produce?

Answer 15

8-10 inches

Question 16

How many blades does a backward inclined flat blade fan usually have?

Answer 16

10-20

Question 17

What is the purpose of curved blades on a backward curved centrifugal fan?

Answer 17

Aerodynamic shape reduces noise levels and power requirements

Question 18

Deficiencies of backward curved fan blade when compared to forward?

Answer 18

Larger and produces humming noise

Question 19

How fast is backward inclined airfoil fan rotated?

Answer 19

3-4 times higher than forward curved fans

Question 20

What static do radial tip fan blades operate at?

Answer 20

Medium to high discharge pressure. Greater than 2” (medium) and greater than 7” (high)

Question 21

Wheel size for radial tip fan blades?

Answer 21

20.5 - 90.75 inches

Question 22

Describe a radial fan blade

Answer 22

Straight, flat, paddle type, mounted perpendicular to shaft

Question 23

How much static does radial fan blade produce?

Answer 23

It can generate high static pressure (over 10”)

Question 24

What static does forward curved centrifugal produce?

Answer 24

Low (less than 2”)

Question 25

Greatest diameter forward curved fan blade?

Answer 25

24"

Question 26

2 applications for a cross flow fan?

Answer 26

Air curtains, ductless split AC evaporators

Question 27

Another name for a mixed flow fan?

Answer 27

Tubular centrifugal

Question 28

Application for a mixed flow fan?

Answer 28

Supply and return air when low sound levels are critical

Question 29

6 things to consider when selecting the right fan?

Answer 29

1. Static and velocity requirements 2. Efficiency (HP requirements) 3. Noise 4. Air quality 5. Physical fan size 6. Initial cost

Question 30

Backward curved fan blade tip velocity vs air velocity?

Answer 30

Tip velocity is greater than air velocity making it suited for high pressure low volume applications

Question 31

Most important when selecting fan blade type?

Answer 31

Static pressure vs air volume

Question 32

How does air density affect CFM?

Answer 32

It does not

Question 33

If you want to double rotational speed of centrifugal fan what happens to HP requirements?

Answer 33

Factor of 8 times larger

Question 34

Increased air temperature does what to motor current?

Answer 34

Decrease motor current (higher temp is less dense)