Fans Part 1Pumps, Fans, Compressors--TurbomachinesPumps, Fans, Compressors—Turbomachines (Review)Fan StandardsFan OperationSelection ConsiderationsFan ClassificationAxial-flow FansPropeller FansTube-Axial FansVane-Axial FansCentrifugal FansStraight or Radial-Tip FansBackward-Curved-Tip FansForward-Curved-Tip FansCross-Flow (or Tangential) FansMixed-Flow FansPerformanceFan CurvesSlide 20Fan Law ExampleSlide 22Sound Power LevelsMore Fans…BAE2023 1Dr. C. L. JonesBiosystems and Ag. EngineeringFans Part 1•Reading: –Chapter 5 in Henderson/Perry–Greenheck Product Application Guide–Dwyer Manometer Guide–AMCA Fan Curve GuideBAE2023 2Dr. C. L. JonesBiosystems and Ag. EngineeringPumps, 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…….BAE2023 3Dr. C. L. JonesBiosystems and Ag. EngineeringPumps, 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 pressureBAE2023 4Dr. C. L. JonesBiosystems and Ag. EngineeringFan Standards•ASHRAE: American Society of Heating, Refrigeration, and Air conditioning Engineering…research and standards•AMCA: Air Movement and Control Association…standardsBAE2023 5Dr. C. L. JonesBiosystems and Ag. EngineeringFan 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 pressureBAE2023 6Dr. C. L. JonesBiosystems and Ag. EngineeringSelection 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 implicationsBAE2023 7Dr. C. L. JonesBiosystems and Ag. EngineeringFan 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 flowBAE2023 8Dr. C. L. JonesBiosystems and Ag. EngineeringAxial-flow Fans•Propeller•Tube-Axial•Vane-AxialBAE2023 9Dr. C. L. JonesBiosystems and Ag. EngineeringPropeller 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)BAE2023 10Dr. C. L. JonesBiosystems and Ag. EngineeringTube-Axial Fans•Wheel or impeller within a tube•Blades are warped for efficiency•Operates at higher pressures and higher ME than propeller fansBAE2023 11Dr. C. L. JonesBiosystems and Ag. EngineeringVane-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 eliminatedBAE2023 12Dr. C. L. JonesBiosystems and Ag. EngineeringCentrifugal 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 tipBAE2023 13Dr. C. L. JonesBiosystems and Ag. EngineeringStraight 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 pressuresBAE2023 14Dr. C. L. JonesBiosystems and Ag. EngineeringBackward-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 airBAE2023 15Dr. C. L. JonesBiosystems and Ag. EngineeringForward-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 blowersBAE2023 16Dr. C. L. JonesBiosystems and Ag. EngineeringCross-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 pressuresBAE2023 17Dr. C. L. JonesBiosystems and Ag. EngineeringMixed-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 agriculturalBAE2023 18Dr. C. L. JonesBiosystems and Ag. EngineeringPerformance•Tested at shutoff and free delivery conditions•Shutoff: discharge is blanked off•Free delivery: outlet resistance is 0BAE2023 19Dr. C. L. JonesBiosystems and Ag. EngineeringFan 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)BAE2023 20Dr. C. L. JonesBiosystems and Ag. EngineeringFan Curves•Fans follow the affinity laws (ASHRAE)BAE2023 21Dr. C. L. JonesBiosystems and Ag. EngineeringFan Law Example•Fan speed N changesfrom 600 to 650 rpm fora fan of a given sizeBAE2023 22Dr. C. L. JonesBiosystems and Ag. EngineeringFan 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:22t svp pr= +QvA=ttp QeP=ssp QeP=BAE2023 23Dr. C. L. JonesBiosystems and Ag. EngineeringSound 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. 010logWLW� �=� �� �BAE2023 24Dr. C. L. JonesBiosystems and Ag. EngineeringMore Fans…•Fans in parallel:
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