Title: Fans Part 1
1Fans Part 1
- Reading
- Chapter 5 in Henderson/Perry
- Greenheck Product Application Guide
- Dwyer Manometer Guide
- AMCA Fan Curve Guide
Dr. C. L. Jones Biosystems and Ag. Engineering
2Pumps, Fans, Compressors--Turbomachines
- Turbomachines change energy level of flowing
fluid by means of momentum exchange - Wide spread in ALL industries
- Power units cars/trucks, tractors
- Computers
- Grain elevators
- Oilfield
- Medical facilities
- Food processing
- And.
Dr. C. L. Jones Biosystems and Ag. Engineering
3Pumps, Fans, CompressorsTurbomachines (Review)
- Differences between pumps, fans, compressors
- Pumps move liquids
- Fans move gases with little increase in
pressure - Compressors move gases with greater increase in
pressure
Dr. C. L. Jones Biosystems and Ag. Engineering
4Fan Standards
- ASHRAE American Society of Heating,
Refrigeration, and Air conditioning
Engineeringresearch and standards - AMCA Air Movement and Control
Associationstandards
Dr. C. L. Jones Biosystems and Ag. Engineering
5Fan Operation
- Fans cause pressure increase by
- Centrifugal force created by rotation of the
column of air trapped between two blades - Kinetic energy is supplied to the air through the
impeller - Total pressure velocity head static pressure
Dr. C. L. Jones Biosystems and Ag. Engineering
6Selection Considerations
- Quantity of air to be moved per unit time
- Estimated system resistance and expected
variations - Amount of noise permitted
- Space available for fan
- Economic implications
Dr. C. L. Jones Biosystems and Ag. Engineering
7Fan Classification
- Designated as dynamic pumps
- Centrifugal
- Further classification by entry and exit of
fluid/gas through impeller - 4 aerodynamic classifications
- Axial flow
- Radial flow referred to as centrifugal fan
- Cross flow
- Mixed flow
Dr. C. L. Jones Biosystems and Ag. Engineering
8Axial-flow Fans
- Propeller
- Tube-Axial
- Vane-Axial
Dr. C. L. Jones Biosystems and Ag. Engineering
9Propeller Fans
- Used in many agricultural ventilation
applications with free delivery or low pressure
conditions - Propeller has a pitch (twist). Distance of air
travel depends on pitch and of blades - Warping the blades prevents back flow of air
(page 121)
Dr. C. L. Jones Biosystems and Ag. Engineering
10Tube-Axial Fans
- Wheel or impeller within a tube
- Blades are warped for efficiency
- Operates at higher pressures and higher ME than
propeller fans
Dr. C. L. Jones Biosystems and Ag. Engineering
11Vane-Axial Fans
- Like a tube axial with guide vanes before or
after the impeller - Higher pressures and efficiencies ( up to 2200
psi and 85 ) because - Vanes direct air flow through a gradual turn
until tangential velocity component is eliminated
Dr. C. L. Jones Biosystems and Ag. Engineering
12Centrifugal Fans
- Consists of wheel or rotor within a spiral
housing - Air makes a 90 degree turn
- Forward-curved-tip
- Backward-curved-tip
- Straight or radial tip
Dr. C. L. Jones Biosystems and Ag. Engineering
13Straight or Radial-Tip Fans
- 6 20 blades
- Blades are 2 to 3 x as long as they are wide
- Larger housing, more expensive
- Can handle dirty air and higher pressures
Dr. C. L. Jones Biosystems and Ag. Engineering
14Backward-Curved-Tip Fans
- Approx. 12 blades
- Flat and tilted backwards
- High speed fan with self-limiting power
- If sized correctly, motor wont overheat if
conditions change (curve pg. 132) - Most efficient
- Cannot handle dirty air
Dr. C. L. Jones Biosystems and Ag. Engineering
15Forward-Curved-Tip Fans
- Up to 60 blades
- Narrow radially but wide parallel to shaft
- Face forward in direction of rotation, scoop
- Low-speed, moderate pressures, can be unstable
- Clean air only
- Lowest noise!!!!!
- Used in many furnace blowers
Dr. C. L. Jones Biosystems and Ag. Engineering
16Cross-Flow (or Tangential) Fans
- Uniform discharge, high air rate
- Use in ovens, baseboard heaters, unit heaters,
drying equipment, kitchen hoods - Larger housing, more expensive
- Can handle dirty air and higher pressures
Dr. C. L. Jones Biosystems and Ag. Engineering
17Mixed-Flow Fans
- Aka In-line or Tubular Centrifugal fans
- Combines features of centrifugal and vane-axial
fans - Straight-through air flow but performance
characteristics of centrifugal - Quiet like centrifugal
- Used as exhaust fans in homes, commercial and
agricultural
Dr. C. L. Jones Biosystems and Ag. Engineering
18Performance
- Tested at shutoff and free delivery conditions
- Shutoff discharge is blanked off
- Free delivery outlet resistance is 0
Dr. C. L. Jones Biosystems and Ag. Engineering
19Fan Curves
- Manufacturer provides fan curve
- Predicts the pressure-flow rate performance of
each fan - Choose fan according to volumetric flow rate for
your system pressure drop - Choose fan with peak efficiency at or near your
operating point - Sometimes manufacturers use tables instead
(Greenheck Handout)
Dr. C. L. Jones Biosystems and Ag. Engineering
20Fan Curves
- Fans follow the affinity laws (ASHRAE)
Dr. C. L. Jones Biosystems and Ag. Engineering
21Fan Law Example
- Fan speed N changesfrom 600 to 650 rpm fora fan
of a given size
Dr. C. L. Jones Biosystems and Ag. Engineering
22Fan Curves
- If we know static pressure and outlet area, we
can find total pressure - Total pressure includes static and velocity
pressure - If we know power, static efficiency, or total
efficiency, the others can be calculated
Dr. C. L. Jones Biosystems and Ag. Engineering
23Sound Power Levels
- Energy transfer Sound
- In dB
- W0 1 x 10-12 Watts
- W power (W)
- For additional units, see eqtn. 5.6 (H/P)
- Sones One sone represents the loudness of a 1
kHz tone at 40 dB SPL.
Dr. C. L. Jones Biosystems and Ag. Engineering
24More Fans
- Fans in parallel moves curve to the
rightpressure stays the same, flow rate is the
sum - Fans in series moves curve upflow rate stays
the same, pressure is the sum
Dr. C. L. Jones Biosystems and Ag. Engineering