Enhancing mixing efficiency and homogeneity by combining anchor and helical ribbon agitators

Abstract

The anchor mixer and the vertical helical ribbon mixer each offer distinct advantages in terms of mixing efficiency and uniformity. Building on the design of the Anchor Mixer (AM), two new models were developed to obtain a fusion of tangential and axial flow: the Anchor-Inner Helical Ribbon Combined Mixer (AIHRM) and the Anchor-Outer Helical Ribbon Combined Mixer (AOHRM). Numerical simulations and bench tests were conducted to compare the mixing processes and effects of these different mixers. The contact-based and variance-based mixing indices were employed to evaluate the mixing performance. The numerical simulation results demonstrated that the mixing index q reached 0.2 at 10 s within the AOHRM, whereas the AM only achieved a q value of approximately 0.15 at the same interval. The bench test results showed that the coefficient of variation (RSD) for AM decreased from 0.87 to 0.56 with the rotational speed increased, while for AOHRM, the RSD value decreased from 0.66 to 0.37 over the same range of speeds. Meanwhile, the RSD value for AM decreased from 0.96 to 0.40, and for AOHRM, it fell from 0.72 to 0.31 over a different period of mixing time. The combined anchor-helical ribbon mixer significantly obtains a better mixing homogeneity and promotes axial flow. In comparison to the AIHRM, the AOHRM lifts and disperses particles over the particle bed, thereby facilitating more extensive particle position exchange. Additionally, the AOHRM exhibits a wider range of disturbances, which aids in eliminating dead zones at the bottom and sides of the mixing vessel.