Pneumatic Dust Control in Grain Elevators Guidelines for Design Operation and Maintenance (1982) / Chapter Skim
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Exhaust Fans
Exhaust Fans
Pages 37-48
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From page 37... ...
Direct-drive exhaust fans make a more compact assembly than belt-driven fans. Direct drive also insures constant speed by avoiding the slippage that can occur when belt drives are not maintained properly.
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From page 38... ...
38 DISC FAN II 1 BMP SP VOLUME - CFM PROPELLER FAN II BMP SP VOLUME-CFM VANE-AXIAL FAN ui BMP VOLUME - CFM FIGURE 5-1 Axial flow fans. (from "Industrial Ventilation", 16th Edition, 1980)
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From page 39... ...
39 BACKWARD CURVED BLADES s VOLUME - CPU STRAIGHT OR RADIAL BLADES VOLUME-CFM n il FORWARD CURVED BLADES VOLUME - CFM FIGURE 5-2 Centrifugal fans. (from "Industrial Ventilation", 16th Edition, 1980)
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From page 40... ...
Fan Size and Speed The size and speed of the exhaust fan for a specific installation should be selected for maximum efficiency. That is, the fan should supply the required airflow and static pressure at minimum horsepower and thus minimum operating cost.
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From page 41... ...
(from "Industrial Ventilation", 16th Edition, 1980) Volume Volume POOR SELECTION GOOD SELECTION Fan with flat pressure curve gives wide volume Fan with steep pressure curve gives small volume variation with pressure change.
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From page 42... ...
Fans for Nonstandard Conditions Rating tables and performance charts for exhaust fans normally are based on the density of clean, dry air at standard temperature and pressure. Standard temperature is 70°F; standard pressure is sea-level pressure -- 407.5 inches of water or 29.92 inches of mercury.
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From page 43... ...
4 Design Conditions: 20200 SCFM @ 16" S.P. Duct Velocity - 4000 fpm SP - Static Pressure TP -- Total Pressure HP -- Horsepower SE - Static Efficiency Octane Band TE - Total Efficiency PWL-Outlet 1 2 3 4• 5 6 7 8 109 105 104 107 102 98 94 90 -- 80 -- 5 60 ^o: 40 -- 5 20 cc co S.P.
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From page 44... ...
flow. The reason is that nonuniform flow increases pressure drop and so decreases volume flow.
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From page 45... ...
L/D = 2V? 5 7Vi I0 CFM loss - I2% Additional fan 10% SP needed 7% S% 30% 24% I8% I 2% 6% FIGURE 5-6 Probable effects of various inlet connections.
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From page 46... ...
Fan Location Nonuniform flow, as well as other problems, can be avoided or minimized by selecting the optimum location for a fan. If at all possible, the installation should conform to these guidelines; 1.
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From page 47... ...
In any event, extreme care should be exercised when considering the use of booster fans. Generally they will handle grain dust and so must be spark-proof and otherwise properly selected for a dust location.
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