GB848131A - Improvements in and relating to centrifugal fans - Google Patents

Abstract

848,131. Centrifugal fans. SELBACH, A., AMME, P., and AMME, W., [trading as POLLRICH & CO., P.]. March 17, 1958 [March 25, 1957], No. 8414/58. Class 110 (1). In a centrifugal fan with a drum-type impeller in which the outlet ends of the blades are curved forwardly into the direction of rotation, the blade exit angle #2, Fig. 5, is between 0 and 10 degrees, and the camber angle α is between 115 and 145 degrees. The use of a small exit angle #2 ensures that the direction of the absolute exit velocity does not deviate sufficiently from the tangential direction at high mass flow to cause energy losses by breaking up the vortex motion about the impeller eye within the casing induced by the current of air leaving the impeller. The exit angle #2 may be negative, i.e., the outlet ends of the blades may be curved forwardly beyond the point at which #2=0. The camber angle α is sufficiently large to cause the flow channels to converge towards the blade exits (after a slight initial divergence), as shown in Fig. 7, so as to produce an acceleration that suppresses flow discontinuities and turbulence. The blade inlet angle #1 is preferably 40 to 50 degrees, sufficiently large to give large flow coefficients at low speeds of rotation.