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 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) 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 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 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 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 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 Propeller Tube-Axial Vane-Axial Dr. C. L. Jones Biosystems and Ag. Engineering BAE2023

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

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

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 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… 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