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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 curves1

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 curves2

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


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