GB758906A - Improvements in or relating to centrifugal fans - Google Patents

Abstract

758,906. Centrifugal fans. WESTING- HOUSE ELECTRIC INTERNATIONAL CO. Dec. 21, 1954 [Dec. 31, 1953], No. 36860/54. Class 110(1) A centrifugal fan comprises hollow aerofoil blades having openings through which gas can be discharged from the blade interior at a variable rate to produce a variable degree of boundary layer flow separation at the blade surfaces, for the purpose of varying the volumetric flow through the fan..Fig. 2 shows a fan having aerofoil blades 23 secured, as by welding or riveting, to a back plate 21 and a shroud 20. Compressed gas from a source 37 flows by way of a valve 33, a pipe 32 and a gas seal 27 to the space between the back plate 21 and a disc 26 attached thereto. The gas enters the interior of each blade 23 by way of a hole 35, Fig. 4, in the back plate 21 and flows out through slots 24, 25 causing flow separation as shown. The resultant reduction in the volumetric flow through the fan is controllable by means of the adjusting handle 38 of the valve 33. A scale 39 may be calibrated in terms of fan volumetric flow. In the modification shown in Fig. 3 the holes 35 are substantially nearer the fan axis than the slots 24, 25, so that gas is drawn in through the holes 35 and discharged from the slots 24, 25 by a centrifugal action, control being effected by a damper ring 40 which is carried by rods 41 slidable in bearings 42 and can be moved towards or away from the holes 35 by means of a lever 50, pinion 49 and rack 48. In a further modification, the supply of gas through the holes 35 is effected by an auxiliary fan attached to the back plate 21 and controllable by a cylinder concentric with the fan shaft and movable axially to obturate the eye of the auxiliary fan to a variable extent. Fig. 8 shows a doubleinlet fan comprising blades 23 on either side of a centre disc 66. Compressed gas from the source 37 is supplied by way of an adjustable valve 79 and an annular seal 80 to holes 77 in one shroud 20 which open into the interiors of the adjacent blades 23. Holes 78 allow gas to pass to the interiors of the blades 23 on the other side of the centre disc 66. The gas passes out through slots 24, 25 in both sets of blades. In a modification, the compressed gas is supplied through an axial bore in the fan shaft, followed by radial passages in the thickened centre disc, each radial passage opening into a transverse bore which opens at each end into blades on either side of the centre disc. A double-inlet version of the fan shown in Fig. 3 is described.