An agitator is generally used in the chemical and food industries, and water treatment plants. The water treatment processes are to be classified into rapid mixing, coagulation, precipitation, filtration and sterilization. Rapid mixing process is the smallest scale and its dispersion time is short. It is a very important process because it gives significant effects on the following processes. A quick injection agitator is used to mix water and many kinds of chemicals. A quick injection agitator has superior mixing characteristics that represent a major step forward in the water treatment. It consists of a motor driven open propeller, which creates a vacuum in the chamber directly above the propeller. This vacuum is transmitted to the chemical metering/control systems by a vacuum line similar to current remote injection systems. The most important design parameters are velocity gradient and dispersion time in a quick injection agitator. Velocity gradient is changed by the shape of the propeller and vacuum in a space between the propeller and the vacuum enhancer. In this study, numerical analyses are carried out to investigate the characteristic of flow in a quick injection agitator with various gaps between the propeller and the vacuum enhancer. A commercial CFD code is used to compute the 3-D viscous flow fields within the propeller of the agitator. Numerical results are graphically depicted with different velocity gradients. Special attention is paid to following topics: pressure distribution, velocity gradient, and void fraction.

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