Fans Part 1 Reading Chapter 5 in HendersonPerry

Fans Part 1 • Reading: – Chapter 5 in Henderson/Perry – Greenheck Product Application Guide – Dwyer Manometer Guide – AMCA Fan Curve Guide BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 1

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……. BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 2

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 BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 3

Fan Standards • ASHRAE: American Society of Heating, Refrigeration, and Air conditioning Engineering…research and standards • AMCA: Air Movement and Control Association…standards BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 4

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 BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 5

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 BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 6

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 BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 7

Axial-flow Fans • Propeller • Tube-Axial • Vane-Axial BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 8

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) BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 9

Tube-Axial Fans • Wheel or impeller within a tube • Blades are warped for efficiency • Operates at higher pressures and higher ME than propeller fans BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 10

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 BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 11

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 BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 12

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 BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 13

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 BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 14

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 BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 15

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 BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 16

Mixed-Flow Fans • Aka In-line or Tubular Centrifugal fans • Combines features of centrifugal and vaneaxial fans • Straight-through air flow but performance characteristics of centrifugal • Quiet like centrifugal • Used as exhaust fans in homes, commercial and agricultural BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 17

Performance • Tested at shutoff and free delivery conditions • Shutoff: discharge is blanked off • Free delivery: outlet resistance is 0 BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 18

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) BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 19

Fan Curves • Fans follow the affinity laws (ASHRAE) BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 20

Fan Law Example • Fan speed N changes from 600 to 650 rpm for a fan of a given size BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 21

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: BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 22

Sound Power Levels • Energy transfer • In d. B: Sound • W 0 = 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 k. Hz tone at 40 d. B SPL. BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 23

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 BAE 2023 Dr. C. L. Jones Biosystems and Ag. Engineering 24