Flow Characteristics In A Stirred Vessel With Double CBY Impellers

Stirred vessels are used in the process industries for a variety of applications. Multiple-impeller stirred tank is widely used in process such as gas-liquid dispersion, high viscous fluid mixing. So the hydrodynamics of the flow is very important for designing and optimization. Most researches of multiple-impeller are focused on the radial impeller, and reports about axial impeller are very few.The flow characteristics in a stirred vessel of diameter 0.476m agitated by double CBY impellers were experimentally investigated by using particle image velocimetry (PIV). The effect of the spacing between the two impellers (C2), the submergence of the upper impeller below the liquid surface (C3), and the clearance of the lower impeller above the base of the vessel (C1) on the flow pattern were investigated. The PIV results show that when C2 less than a critical value,0.65T, a whole axial circulation is formed in the vessel, otherwise, the circulation is separated into two smaller ones. The submergence (C3) has little effect on the velocity near the impeller region. With the decreasing of C1, the radial flow generated by the lower impeller, the axial flow generated by the upper impeller, and the axial flow of the main circulation increased. The results are of importance to the design and optimization of industrial multiple CBY impeller stirred vessel.