On the Racing Power of Impellers

Abstract

Measurements of the torque consumed by an impeller rotating in a closed vessel were taken under various geometrical configurations by means of a torsion balance technique. The experimental results give the following conclusions : (1) When the boss ratio has a value between zero and 0.6, the resisting coefficient takes a constant value approximately. (2) The resisting coefficient takes the maximum value for a certain number of blades of the impeller and varies in proportion to (sinθ)^1/2 (θ≐̸0) where θ is the attack angle of blades. (3) The relation between the resisting coefficient C_f and Reynolds number R₆ in a smooth vessel is given by C_f ∽ R₆^-1/6. (4) When the width of the impeller is large, the resisting coefficient of the impeller is identical with that of a disc with ribs on both sides of the surfaces. (5) The effect of the number of blades disappears when the impeller has a shroud and the angle of blade is larger than 45 degrees.