Abstract Computational fluid dynamics (CFD) was applied to investigate the flow characteristics in an industrial polymerization tank with double layer helical coils. Herschel-Bulkley model was applied to describe the rheology of Bingham-pseudoplastic fluid. The effect of Bingham property on the flow was revealed. The helical coils were found to affect the flow pattern, making the axial flow impeller present shortage in overall mixing performance, especially in the area between the coils. The combined impeller, which consists of an axial flow impeller and a large blade radial flow impeller, was proposed to improve the flow close to coils and overall mixing. The comparison results indicated that under the same operational condition, the combined impeller provide a higher average shear rate than the original axial flow impeller, resulting in a decrease in viscosity but a corresponding increase in power consumption. The combined impeller generates effective radial flow through the coils and the axial circulation flow ensures the overall mixing efficiency. In addition, appropriately increasing the impeller diameter ratio is beneficial for further promoting the fluid flow between coils. Effective guidance for the industrial coiled stirred tank with complex rheological properties may be obtained based on the impeller optimization.
Wang et al. (Fri,) studied this question.