Exploration of Multishafts Stirred Reactors: An Investigation on Experiments and Large Eddy Simulations for Turbulent Chaos and Mixing Characteristics

The conventional single-shaft stirred reactor dissipates a significant amount of energy due to the formation of a symmetrical flow field. In an innovative effort to optimize energy distribution and enhance overall turbulent chaos and mixing performance, the use of a multishaft stirred reactor was explored. This inventive approach is inspired by the graceful V-formation flight of geese and the synchronized rowing movements of ducks in water. Experimental and large eddy simulation (LES) studies were conducted on three distinct stirred reactors, and a comprehensive analysis was undertaken, considering various indicators such as mixing time, largest Lyapunov exponent (LLE), wavelet analysis, simulated flow field visualization, swirl number, and secondary flow intensity. The research findings reveal that the flow field of the triple-shaft three-impeller reactor (T-T-STR) is characterized by abundant multiscale vortices, resulting in reduced mixing times. However, at a rotational speed of around 200 rpm, the mixing performance of the T-T-STR deteriorates abruptly, as confirmed by the LLE. This suggests that under a uniform flow structure, local chaotic characteristics alone can reflect the overall changes in turbulent chaos and mixing performance. The fundamental reason for the decline in mixing performance is attributed to the deterioration of the energy cascade effect, as evidenced by variations in mixing performance at different scales. Furthermore, T-T-STR exhibits a near-zero swirl number and a higher secondary flow intensity, indicating superior turbulent diffusion capability, stemming from its unique flow field structure. In summary, during the scaling-up process of stirred reactors, increasing the aspect ratio and the number of shafts can effectively mitigate the amplification effect.