File:A catechism on the combustion of coal and the prevention of smoke; a practical treatise (1900) (14783119885).jpg

Identifier: catechismoncombu00barr (find matches)
Title: A catechism on the combustion of coal and the prevention of smoke; a practical treatise
Year: 1900 (1900s)
Authors: Barr, William M. (William Miller)
Subjects: Smoke prevention Combustion Coal
Publisher: New York, N. W. Henley & Company
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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nce they are dischargedthrough a short, vertical stack. The experimental resultsobtained furnish an interesting commentary upon the re-lations between fan speed, volume moved, pressure cre-ated, and horse power required. Up to a certain speedthe natural draft of the short stack is equal to, or actuallyexceeds, that created by the operation of the fans; butwhen the draft produced by the fans exceeds that whichthe stack is capable of creating, the additional work isthrown upon the fans, and the power increases practicallyas the cube of the number of revolutions. Q. What is the proper kind of fan for use in connec-tion with a mechanical draft apparatus ? Two types of fans exist. The first, known as the discor propeller wheel, is constructed on the order of a screwpropeller, and moves the air in lines parallel to its axis,the blades acting on the principle of the inclined plane.The second, or fan blower proper, consists in its simplestform of a number of blades extending radially from the
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328 COMBUSTION OF COAL. axis, and presenting practically flat surfaces to the air asthey revolve. By the action of the wheel the air is drawnin axially at the centre and delivered from the tips of theblades in a tangential direction. This type may be sim-ply designated as the centrifugal fan, or, more properly, asthe peripheral discharge fan. The propeller or disc fan is practically useless as ameans of draft production. The desired results can besecured only by the use of the peripheral discharge type. Theoretically there should be a difference in the formof wheels designed for creating pressure and creating avacuum; practically the distinction between a blower andan exhauster is one of adaptation rather than of construc-tion. Q. What are the advantages claimed for mechanicaldraft ? The advantages claimed may be summarized, for landrequirements as distinguished from marine, in that by itsintroduction greater economy in the first cost or runningexpense of a steam plant may be secured.

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