Evaluation of axial dispersion and mixing performance in oscillatory baffled reactors using CFD

Background: The paper reports extensive CFD work and analyses of an oscillatory baffled reactor (OBR) planned to be used for the production of polyaniline continuously. In the polyaniline process, viscosity changes during the course of the reaction. Two non‐Newtonian fluids were used to represent the stages of fluids during the reaction in a simulation, in addition to water as the reference fluid. Two quantitative measures derived from the CFD results are employed to evaluate OBR reactor performance: the axial dispersion coefficient and the ratio of axial and transverse velocities.

Results: The CFD data showed that the dispersion coefficient as a function of viscosity exhibits a maximum for given oscillation parameters. In the turbulent regime, the axial dispersion is often correlated with the oscillatory Reynolds number in OBR or equivalent Reynolds numbers in other reactor devices. In the high viscosity regime, such a general correlation is not valid for different operational parameters. The results of the CFD simulations in the moving baffle‐OBR indicate, for the first time, that the axial dispersion coefficients in the moving baffle arrangement is 10–17% higher than that in the moving fluid type, due to enhanced shear rate in the former device. This quantitative information is valuable for the design and smooth transition from batch to continuous reactors. 

Conclusion: The established dependence of axial dispersion and the ratio of axial to transverse velocities on both viscosity and the operational parameters enhanced the understanding of mixing and dispersion characteristics of the OBR. The CFD analysis supplied the information needed to determine the design parameters for the reactor used in continuous production of polyaniline.