Mechanics of Air Machinery (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1904 edition. Excerpt: ...to be infinitely great. Therefore when radial vanes are employed the entrance of the u 2 air is attended with a loss of work jQy-The loss due to impact is generally expressed by (u, --v, cot a)2 2-g Qr for the tangential component of the entrance velocity v cot a is suddenly transformed into uv Rittinger's experiments also showed that the performance was small when flat radial vanes were employed, the highest efficiency in this case being only 0.08. Tf we give the vanes a flat form AB', Fig. 60, which cuts the inner circumference of the wheel at an angle a, the triangle ABC gives for the angle /?, formed by the vane with the outer T COs p circumference, the expression--=-. r r2 cos a With this form of vane the ratio of the relative velocities Fig. 60. of the air at the entrance and exit becomes, neglecting the thickness of the vanes, c2 _ r, Z, sin a _ l1 tan a ci r2l2 sin /? l2 tan /?' In order that the efflux may take place with full buckets we must have c2cu. hence we must make l2 tan 8y Z1 tan a. But with curved arms for which the aforesaid dependence of 3 or a does not exist we have c2 _ rlli sin a c, r2l2 sin /?' The remarks made in connection with the form of the blades of centrifugal pumps apply here also. Rittinger recommends that circular arcs be chosen and that the outer vane-angle /3 be assumed equal to 90. The center O of such a vane AB" lies on a perpendicular to the direction AB' of the vane at A, and the radius p=OB" is obtained by equating the two values given for CO by the triangle CB"O and CAO. Accordingly we have CO2 = ra2+p2 = r2+p2 + 2r1p cos a, from which follows 2r, cos a' If we do not make the outer angle /?=90, but choose some other value for /?, the arc for the vane can easily be constructed as...