Importance

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Abstract

Impellers are provided which enhance the efficiency of surface aeration of a liquid, for example, liquid contained in open aeration tanks, in terms of the mass of oxygen transferred per hour to the liquid per horsepower used in driving the impeller. The impeller is an axial flow impeller and may be either a pitched blade turbine (PBT) or have airfoil shaped blades. In either case, the impeller has a portion which extends radially along an edge thereof which projects above the surface of the liquid being mixed in a vertical direction, a sufficient distance to substantially prevent flow of the liquid over the top edges of the blades of the impeller. Preferably, the impeller is rotated in an up-pumping direction and propels the liquid being aerated in a radially outward direction. A sufficient upward surge of liquid is produced so that the liquid is observed to splash back onto the surface a plurality of times in the course of operation of the impeller. Such multiple splashing action enhances the contact between the air and the liquid and lends itself to the improved efficiency of aeration.

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First Claim