Residence Time Distribution in a Static Mixer

Static mixers, as reviewed in Chapter 7, contain mixing elements enclosed in a tubular housing through which radial mixing is achieved. They redistribute fluid across the flow channel and consequently rearrange temperature and composition distributions. They are often used to promote mixing in laminar flow systems thus having a pronounced effect on the RTD. 

Computational fluid dynamics (CFD) is an effective tool in analyzing the velocity distribution and other pertinent parameters in a static mixer. CFD is also being recognized as an effective tool in enhancing the performance of mixers and reactors, which is reviewed in Chapter 10. 

The dispersed plug flow model has been successfully applied to describe the flow characteristics in the Kenics mixer. The complex flow behavior in the mixer is characterized by the one-parameter. The Peclet number, NPe, is defined by  

The Kenics mixer has been shown to provide thorough radial mixing. This results in a reduction in radial gradients in velocity, composition, and temperature. Because the unit possesses nearly plug flow characteristics, both temperature and product quality controls are achieved. 

Using the experimental residence time distribution data of Levenspiel and Smith in Example 8-2, determine the number of ideal tanks N, the variance, dispersion number, and Peclet number. 

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