Effect of inner cylinder configuration on liquid droplet dispersion and size distributions in a Taylor-Couette reactor

Effect of varying surface structures of the inner rotating cylinder on characteristics of droplet formed in a liquid–liquid Taylor-Couette (TC) reactor is investigated. Two novel surface structures of inner cylinders, designed with axially corrugated surface (N40) and with typical three-dimensional roughness (NZ40), respectively, were adopted for the investigation. The high-speed camera visualization was used to measure the droplet size while CFD modelling was applied to predict the fluid dynamics of TC flows with such two inner cylinders and a smooth surface inner cylinder, thus revealing the effect of inner cylinder configuration on the droplet formation in the TC flows. The experimental results have clearly indicated that both the rotation speed and surface configuration variation of the inner cylinders affect the generated droplet size and distribution. As the rotation speed increases, the droplet size is obviously reduced for all types of inner cylinder configurations. Compared with the conventional smooth surface inner cylinder, the two new types of inner cylinders with special surface structures can produce much smaller droplets, especially for the case of N40 surface structure inner cylinder, with which the smallest droplet size was found at all the experimental conditions. CFD modelling results have demonstrated that the surface configurations of inner cylinder can significantly affect the turbulence generation, consequently altering the distributions of turbulent kinetic energy and local turbulence shear strain rate. As a result, the droplet size was found to be controlled by the change of the local turbulent dissipation rate that was strongly associated with the surface structures of inner cylinders. Empirical correlations that correlate the droplet size with the Weber number and Reynolds number were proposed based on the high-speed camera visualization data.