Scale-up of Single Phase Non-Reactive Turbulent Stirred Tanks

5 Scale-up of Single Phase Non-Reactive Turbulent Stirred Tanks 

Mixing properties and flow fields in stirred tanks are usually studied on a laboratory scale. Practical scale-up of a stirred tank cannot be performed requiring that every individual mixing and fluid mechanical parameters in the small scale tank should be maintained in the larger one. Therefore, scale-up procedures for different types of processes have been determined through experience, testing and computational fluid dynamics simulations. 

Over the years several guidelines have been developed for the optimal scale-up of stirred tanks, usually reflected through the concepts of geometric-, dynamic- and kinematic similarities [65]. Geometric similarity means that all the pertinent dimensions are similar and have a common constant ratio. Kinematic similarity requires that all the velocities at the two different scales have a common constant ratio. Dynamic similarity requires that all pertinent force ratios must have a common constant ratio. 

The concepts of similarity suggest the use of dimensionless groups. There are, however, other process parameters that could be held constant. Such parameters could be, the blending time, the power per unit volume, the superficial gas velocity, the shear rates and the heat transfer coefficient. Which scale-up criteria that should be chosen depends on the actual process, since the sensitivity to each parameter appears to be different for the various processes. 

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