GB401625A - Improvements in and relating to rotary fans - Google Patents

Abstract

401,625. Screw fans. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of McMahan, K. D. ; 919, Brandywine Avenue, Schenectady, New York, U.S.A.) July 31, 1933, No. 21496. Convention date, July 30, 1932. [Class 110 (i).] Each blade 11 of a screw fan has a forwardly extending trailing portion 16 terminating in a trailing edge 15 substantially in the. form of an involute curve ; the action of this portion tends to balance the inward momentum of the air coming from the portion near the outer periphery of the blade. The leading edge 13 is slightly curved, and the peripheral edge 14 extends a greater distance from the fan axis near the leading edge than it does near the trailing edge. The shape of the edge prevents air from being picked up by the periphery between the leading and trailing edges. The outer portion 17, which may comprise about one-third of the radial extent of the blade surface, extends rearwardly as regards the direction of air flow with respect to the remainder of the blade. The inner end of the blade makes a greater angle with the plane of rotation than the outer end, and the blade as a whole extends forwardly as regards the direction of air flow with respect to a line perpendicular to the fan axis. This construction tends to reduce the peak velocity of the current from the blade and to increase the velocity from the inner part of the blade so giving an improved velocity distribution with consequent noise reduction.