Modeling of Annular Reactors

Due to the small dimensions and the typical low flows used in laboratory reactors, a laminar flow pattern is established in the annular reactor. The concentration profile will flatten out due to radial diffusion. In an annular reactor. 

Raja et al. [47] derived the following criterion to assume plug flow conditions (flat concentration profile)  

For Da 0.1, external mass transfer can be neglected. Before this criterion can be used, the reaction rate must be known. To circumvent this issue, Berger and Kapteijn [48] proposed an easier to use criterion based on the conversion to check the absence of external diffusion limitations  

As long as the conversion is below the value of the right-hand side term, the external diffusion limitations can be neglected. On the other hand, the external mass transfer can be taken into account by a mass transfer coefficient for which Beretta et al. [45] derived the following correlation based on a functional form for the local Sherwood number to interpolate the exact solution  

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