Cyclopedia of heating, plumbing and sanitation; a complete reference work . Pig. 146. Cone Fan. Discharges through Opening In Wall into a Plenum ChamberConnecting with Distributing Ducts. Theory of Centrifugal Fans. The action of a fan is affected to such an extent by the various conditions under which it operates,that it is impossible to give fixed rules for determining the exactresults to be expected in any particular instance. This being thecase, it seems best to take up the matter briefly from a theoretical 173 h\\ HEATING A\D VENTILATION standpoint, and then show what corrections arc nece
Cyclopedia of heating, plumbing and sanitation; a complete reference work . Pig. 146. Cone Fan. Discharges through Opening In Wall into a Plenum ChamberConnecting with Distributing Ducts. Theory of Centrifugal Fans. The action of a fan is affected to such an extent by the various conditions under which it operates,that it is impossible to give fixed rules for determining the exactresults to be expected in any particular instance. This being thecase, it seems best to take up the matter briefly from a theoretical 173 h\\ HEATING A\D VENTILATION standpoint, and then show what corrections arc necessary in thecase of ;i given fan under actual working conditions. There are various methods for determining the capacity of afan at differenl speeds, and the power necessary to drive it; eachmanufacturer has his own formulae for this purpose, based upontests of his own particular fans. The methods given here applyin a general way to fans having proportions which represent theart rai/i of several standard makes; and the results obtained will he. Fi«. 147. Small, Direct-Connected Exhauster for Ventilating Toilet-Rooms, Chemical Hoods, etc. found to correspond well with those obtained in practice underordinary conditions. As already stated, the rotation of a fan of this type sets in motionthe air between the blades, which, by the action of centrifugal force,is delivered at the periphery of the wheel into the casing surroundingit. As the velocity of flow through the discharge outlet dependsupon the pressure or head within the casing, and this in turn uponthe velocity of the blades, it becomes necessary to examine brieflyinto the relations existing between these quantities. 174 HEATING ANT) VENTILATION 161 Pressure. The pressure referred to in connection with a fan,is that in the discharge outlet, and represents the force which drivesthe air through the ducts and flues. The greater the pressure with agiven resistance in the pipes, the greater will be the volume of airdelivered; and
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