The Effect of Entrance and Discharge Angles on the Performance of a Centrifugal Fan

Abstract

Abstract In this paper the authors discuss tests conducted by them to determine the variations in the operating characteristics of a back-ward-curved-blade fan as affected by (a) blade entrance angles, (b) blade discharge angles, and (c) fixed entrance and discharge angles but with different wheel diameters. A brief discussion of static pressure in a centrifugal fan, with the development of equations, opens the paper. Then follows a description of the test unit, and the method of conducting the tests. A discussion of observed results, in which several sets of curves are introduced, forms the body of the paper. The authors reach the conclusion that loss by shock at entrance is influenced by the entrance angle. With constant entrance blade angles and diameter of wheel, the pressure and capacity are increased with increase in the value of the blade discharge angle. The shape of the passage way through the wheel is recognized as a factor in fan losses. Increasing diameter of symmetrical wheels, used in the same housing and operated at constant tip speed, was found to increase the pressure-capacity characteristics and greatly improve the efficiency.