(87b) Thixotropic Suspensions in Static Mixer: Comparison of Different Structure-Based Models

Thixotropy is one of the most challenging problems in colloid rheology. A comprehensive definition for thixotropy proposed by Mewis and Wagner (2009) as “...the continuous decrease of viscosity with time when flow is applied to a sample that has been previously at rest, and the subsequent recovery of viscosity when the flow is discontinued”. This behavior of the working fluid is very common in industrial applications. Thixotropy can be encountered in many industrial applications, including the processing of pharmaceuticals, minerals, food products, coatings, paints, gels, inks, drilling muds, concrete, etc. In this work, we investigate thixotropic behavior of the fluid in a static mixer by using numerical techniques.

In this work, using SIMCENTER STAR-CCM+ a continuum approach based on structure variable transport equation was adopted to account structure buildup and breakdown in the fluid. We used different structure models proposed by Mujumbar et al (2002), Houska (1980), and Coussot et al (2002), to analyze mixing pattern and viscosity decay in static mixer. Furthermore, irreversible structure model also investigated, and the results were compared with proposed reversible material models. Our numerical approach was fully verified by comparing the fluid flow properties and structure variable results with those reported in the literature.

Mewis, J., & Wagner, N. J. (2009). Thixotropy. Advances in Colloid and Interface Science, 147, 214-227.

Mujumdar, A., Beris, A. N., & Metzner, A. B. (2002). Transient phenomena in thixotropic systems. Journal of Non-Newtonian Fluid Mechanics, 102(2), 157-178.

Houska, M. Inzenyrske aspekty reologie tixotropnich kapalin. Diss. Ph. D. thesis, Technical University of Prague, Praha, Czechia, 1980.

Coussot, P., Raynaud, J. S., Bertrand, F., Moucheront, P., Guilbaud, J. P., Huynh, H. T., & Lesueur, D. (2002). Coexistence of liquid and solid phases in flowing soft-glassy materials. Physical review letters, 88(21), 218301.