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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. Engineering . Pumps, Fans, Compressors--Turbomachines.

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fans part 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

BAE2023

pumps fans compressors turbomachines
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

BAE2023

pumps fans compressors turbomachines review
Pumps, Fans, Compressors—Turbomachines (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

BAE2023

fan standards
Fan Standards
  • ASHRAE: American Society of Heating, Refrigeration, and Air conditioning Engineering…research and standards
  • AMCA: Air Movement and Control Association…standards

Dr. C. L. Jones

Biosystems and Ag. Engineering

BAE2023

fan operation
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

BAE2023

selection considerations
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

BAE2023

fan classification
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

BAE2023

axial flow fans
Axial-flow Fans
  • Propeller
  • Tube-Axial
  • Vane-Axial

Dr. C. L. Jones

Biosystems and Ag. Engineering

BAE2023

propeller fans
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

BAE2023

tube axial fans
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

BAE2023

vane axial fans
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

BAE2023

centrifugal fans
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

BAE2023

straight or radial tip fans
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

BAE2023

backward curved tip fans
Backward-Curved-Tip Fans
  • Approx. 12 blades
  • Flat and tilted backwards
  • High speed fan with self-limiting power
    • If sized correctly, motor won’t overheat if conditions change (curve pg. 132)
  • Most efficient
  • Cannot handle dirty air

Dr. C. L. Jones

Biosystems and Ag. Engineering

BAE2023

forward curved tip fans
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

BAE2023

cross flow or tangential fans
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

BAE2023

mixed flow fans
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

BAE2023

performance
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

BAE2023

fan curves
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

BAE2023

fan curves20
Fan Curves
  • Fans follow the affinity laws (ASHRAE)

Dr. C. L. Jones

Biosystems and Ag. Engineering

BAE2023

fan law example
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

BAE2023

fan curves22
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

BAE2023

sound power levels
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

BAE2023

more fans
More Fans…
  • Fans in parallel: moves curve to the right…pressure stays the same, flow rate is the sum
  • Fans in series: moves curve up…flow rate stays the same, pressure is the sum

Dr. C. L. Jones

Biosystems and Ag. Engineering

BAE2023