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Fans Part 1

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Fans 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. – PowerPoint PPT presentation

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Title: Fans Part 1


1
Fans 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
2
Pumps, 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
3
Pumps, 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
4
Fan 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
5
Fan 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
6
Selection 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
7
Fan 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
8
Axial-flow Fans
  • Propeller
  • Tube-Axial
  • Vane-Axial

Dr. C. L. Jones Biosystems and Ag. Engineering
9
Propeller 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
10
Tube-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
11
Vane-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
12
Centrifugal 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
13
Straight 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
14
Backward-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
15
Forward-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
16
Cross-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
17
Mixed-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
18
Performance
  • 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
19
Fan 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
20
Fan Curves
  • Fans follow the affinity laws (ASHRAE)

Dr. C. L. Jones Biosystems and Ag. Engineering
21
Fan Law Example
  • Fan speed N changesfrom 600 to 650 rpm fora fan
    of a given size

Dr. C. L. Jones Biosystems and Ag. Engineering
22
Fan 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
23
Sound 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
24
More 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
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