GB841164A - Improvements in or relating to centrifugal fan embodying airfoil blades - Google Patents

Abstract

841,164. Centrifugal fans. WESTING- HOUSE ELECTRIC CORPORATION. Dec. 4, 1957 [Dec. 10, 1956], No. 37731/57. Class 110 (1). A centrifugal fan impeller comprises backwardly-curved aerofoil blades having slots in their gas impacting sides, near their trailing edges, gas being supplied under pressure into the blades and discharged through the slots at an angle of between 30 and 120 degrees to the camber line of each blade, whereby the gas deflects the main gas stream outwardly from the trailing edges. The discharge pressure of a centrifugal fan can be increased by blowing compressed air from the interior of each impeller blade 11A, Fig. 6, through a slot 24A situated near the trailing edge of the pressure or convex side of the blade, so as to deflect the main air stream outwardly from the trailing edge. The slot 24A, the width of which is preferably between 0.5 and 10% of the chord length of the blade, is at an angle # of between 30 and 120 degrees to the camber line. The compressed air may be supplied from an external source, passing through the hollow impeller shaft and thence through radial passages in the centre plate or back-plate of the impeller to the blade interiors, as described in Specification 780;464. Alternatively, the compressed air may be supplied by an auxiliary centrifugal fan attached to the impeller backplate, the flow being controllable by a cylinder concentric with the impeller shaft and movable axially to obturate the eye of the auxiliary fan to a variable extent, as described in Specification 758,906. Further alternatives are shown in Fig. 7, in which air is forced by ram action into the interior of a blade through a slot 40 in its leading edge. This slot may instead be situated in the pressure side of the blade at a short distance from the leading edge, with a lip 42 to act as a scoop. Reference has been directed by the Comptroller to Specifications 758,906 and 780,464.