Flow and mixing analysis of a thixotropic fluid in a barrier-embedded partitioned pipe mixer (BPPM): A numerical study

Flow and mixing characteristics of a thixotropic fluid in a static mixer were numerically investigated in this study. We selected a barrier-embedded partitioned pipe mixer (BPPM) as the model static mixer, whose geometric design parameters are fixed for the simplicity of the analysis. The Moore structure-kinetics model was employed to describe a thixotropic fluid, whose flow and mixing characteristics were systematically analyzed for cases with specific combinations of three dimensionless numbers: the apparent Reynolds number (Rea), thixotropy number (Th), and destruction parameter (kd). The structure parameter (λ) showed a highly reduced value near the barrier tip, where the highest shear deformation occurred. The average λ dramatically decreased with Th as the fluid thixotropy becomes significant. kd is related to the standard deviation of λ because it controls the magnitude of the material derivative of λ. As Rea increased, more complex flow and mixing behaviors were observed, especially at a higher Th. From the qualitative and quantitative analyses of the Poincaré section and flux-weighted intensity of segregation (Id), the mixing performance was seen to improve with Th in the counter-rotational BPPM, while a more complex trend of the degree of mixing was found in the co-rotational BPPM. This study provides a comprehensive understanding of thixotropic fluid mixing with an emphasis on the complex relationship between the flow characteristics and mixing performance.