(711a) Effect of Tracer and Fluid Behavior on Mixing Performance of High Shear Mixers

High shear mixers (HSMs) broadly used in industrial to biological processes, such as cosmetics, paints, food, healthcare, coatings, etc., where intense rate of mixing, uniform emulsification and dispersion of fluids play a significant role (Vashisth et al. 2021). The flow fields and mixing in high shear mixers are intensified by applying high shear through narrow gaps between the rotor and stator geometries. In this study, the mixing performance for Newtonian and non-Newtonian fluids is analyzed for different HSMs. Three-dimensional numerical simulations are carried out for different stator heads HSMs such as disintegrated (18 stator holes), mesh (63 stator holes) and slotted (9 stator holes) at different rotor speeds (4000, 6000 and 8000 rpm). Standard k-É› turbulence (Vikash et al. 2017) and Power law (Zhang et al. 2017) models are used for the investigation of fluid dynamics of Newtonian and non-Newtonian fluids. Further, species transport model without reaction model is used for mixing characterization and simulations are run for flow time of 40 seconds for mixing characterization. The overall results suggested that mixing is a function of design of stator head, fluid behavior, rotor speed and tracer location (Figure 1(ii) and (iii)). In smaller stator holes HSM, cavern effect has been observed for viscous fluids and no improvement in the mixing is observed after certain flow time. Mixing time (t₉₅) is estimated for different HSMs for Newtonian fluid and a good agreement is found with the existing findings. For larger (slotted head) and smaller stator (mesh head) holes HSMs the mixing parameter constant (a) are found as 20.33 and 31.21, respectively, which is in line with the results available in the literature (James et al. 2017). However, the mixing constant is more than the stirred impellers (Grenville 1992). Further, it is observed that the tracer injection location has significant effect on the mixing performance. Tracer is injected at three different locations such as below the rotor-stator assembly (center of the bottom plate opening), top and bottom of the mixing tank (Figure 1(i)). Several locations are marked to monitor the mass fraction of tracer to investigate the mixing time and uniformity of tracer inside the mixing tank with time and rotor speed. Flow fields are also observed for different HSMs. Maximum strain rate is observed in the gap between rotor and stator and the rotor region and decreased with an increase in the radial distance. The findings provide a good estimation for further selection and development of HSMs.

References

1. Grenville, R. K., 1992. Blending of viscous Newtonian and pseudo-plastic fluids, Ph.D. dissertation, Cranfield Institute of Technology, Cranfield, Bedfordshire, England.
2. James, J., Cooke, M., Trinh, L., Hou, R., Martin, P., Kowalski, A., Rodgers, T.L. 2017. Scale-up of batch rotor-stator mixers. Part 2–mixing and emulsification. Chem. Eng. Res. Des. 124, 321-329.
3. Vashisth, V., Nigam, K.D.P., Kumar V., 2021. Design and development of high shear mixers: fundamentals, applications and recent progress. Chem. Eng. Sci. 232, 116296.
4. Vikash, Deshawar, D., Kumar V., 2017. Hydrodynamics and mixing characterization in a novel high shear mixer. Chem. Eng. Process. Process Intensif. 120, 57-67.
5. Zhang, C., Gu, J., Qin, H., Xu, Q., Li, W., Jia, X., Zhang, J., 2017. CFD analysis of flow pattern and power consumption for viscous fluids in in-line high shear mixers. Chem. Eng. Res. Des. 117, 190–204.