CFD simulation of shear flow and mixing in a Taylor–Couette reactor with variable cross-section inner cylinders

Abstract

A Taylor–Couette (TC) reactor has been considered as a promising technology to produce uniform ultra-fine particles with controlled morphology and size because of its rather narrow shear rate distribution in comparison to a conventional stirred tank. However, small particles in the TC reactor are likely entrapped by the Taylor vortices and concentrated more in the core of the vortices, thus having an adverse or a positive impact on producing the uniformly fine particles. To mitigate this disadvantage, one approach is to adopt an inner cylinder with a variable cross-section through the proper design to obtain a non-constant gap between the inner and outer cylinders in the TC reactor. This study investigates the use of specific profiles of the cross section for the inner cylinder to deform the Taylor vortices, effectively reducing the regions of low velocity and shear rate in the TC reactor. The profiles are composed of a series of curves. The flow patterns and shear rate distributions in the modified TC reactors were investigated using CFD modelling. The sliding mesh method and the Reynolds stress model were employed in the simulation to account for highly turbulent rotating flows. The simulated results compared with those for the classical TC reactor clearly indicate that the regions of low shear rate are effectively reduced in the modified TC reactors because the Taylor vortices occurring in the gap becomes temporal-periodic with respect to the stationary outer cylinder. The obtained shear rate distributions are remarkably narrower than those of the classical TC reactor. It was revealed that the curvature of curves for the cross-section profiles can significantly affect the shear rate distributions, and there exists an optimal profile for the inner cylinder cross-section.