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

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
BAE2023

3. 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

4. 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

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
BAE2023

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
BAE2023

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
BAE2023

8. Axial-flow Fans Propeller Tube-Axial Vane-Axial Dr. C. L. Jones
Biosystems and Ag. Engineering
BAE2023

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
BAE2023

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
BAE2023

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
BAE2023

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
BAE2023

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
BAE2023

14. 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

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
BAE2023

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
BAE2023

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
BAE2023

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
BAE2023

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
BAE2023

20. Fan Curves Fans follow the affinity laws (ASHRAE) Dr. C. L. Jones
Biosystems and Ag. Engineering
BAE2023

21. Fan Law Example
Fan speed N changes from 600 to 650 rpm for a fan of a given size
Dr. C. L. Jones
Biosystems and Ag. Engineering
BAE2023

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
BAE2023

23. Sound Power Levels Energy transfer Sound In dB:
W0 = 1 x 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

24. 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