# Centrifugal Fans; A Theoretical and Practical Treatise on Fans for Moving Air in Large Quantities at Comparatively Low Pressures

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 edition. Excerpt: ...A; n D ac, when a c is less than A; If we let Tc D A be represented by q', and remember that in (39) we have designated the frac (44), when a c is less than A; q' B, when a c is greater than A. a c The value of B for different values of----A is given in Table IV. q' is the air delivered per revolution of the wheel when the fan is working at its capacity and depends upon the blast area of the fan wheel; and the blast area, A, as has been shown, depends upon the ratio, r, of the diameter of the inlet to the diameter of the wheel. To determine q' for any given fan all that is necessary is to multiply the blast area of the wheel as given by Table III. by 7t times the diameter of the wheel. The blast area must, of course, be in square feet, and the diameter of the wheel must be in feet. Table V. gives the value of q' for fans with wheels of different diameters, and for r, the ratio of the diameter of the inlet opening to the diameter of the wheel, equal to 0.625 and to 0.707. TABLE V. Table V. may be used to determine the number of revolutions at which the wheel of a fan must be run to deliver a given number of cubic feet of air per minute when the theoretical outlet area, ac, is equal to the blast area, A. Example: --What must be the speed of a fan wheel whose diameter is 7 feet, and whose inlet diameter is 59 inches, in order to deliver 25000 cubic feet of air a minute. Here r is 'or 0.707. We shall assume that 84 the theoretical outlet area is equal to the blast area. From Table V. we see that when r is 0.707 a 7-foot wheel will deliver 167 cubic feet of air per revolution. Hence to deliver 25000 cubic feet of air per minute a 7-foot wheel must make as many revolutions per minute as 167 is contained in 25000, that is CHAPTER VI. Pressure. When...