Chaotic mixing performance of non-Newtonian fluids in S-Type static mixer and optimization based on response surface methodology

Non-Newtonian fluids play a vital role in industrial production. It is of great significance to study the mixing and chaotic characteristics of flow field in static mixers for the energy utilization. An improved structure of S-Type static mixer is proposed. In order to deeply investigate the flow characteristics of non-Newtonian fluids in S-Type static mixers, experimental and numerical studies are conducted on the mixing efficiency and chaotic behaviors under different flow rates. The PLIF method is adopted to visually study the distribution of CMC solutions with different mass concentrations. It is found that the average deviation of coefficient of variation (CoV) between experiment and Second-order simulation scheme is 4.15%. The simulation results show that the M number in SType-b mixer is 10.13-18.29 %, 10.82-22.26 %, and 20.39-27.35 % higher than that of the Kenics, Komax, and S-Type static mixers, respectively. Additionally, the S-Type-b static mixer exhibits a higher average Lyapunov exponent (LEave) and lower variance of the Lyapunov exponent (LEvar) under different flow rates, which indicates that the S-Type-b static mixer has better flow stability. The structural parameters of S-Type-b mixer are optimized using Response Surface Methodology (RSM) and Non-dominated Sorting Genetic Algorithm II (NSGA-II). The optimal design parameters ensure that the M number of the S-Type-b static mixer is 0.2926 and LEave reaches 5.3246, which significantly improves the mixing efficiency and system stability.