A PIV study to quantify the relationships between viscoelasticity and flow behavior in stirred tanks

• Published in: Chemical engineering science 2023-12, Vol.282, p.119301, Article 119301
• Main Authors: Kolano, Markus, Kraume, Matthias
• Format: Article
• Language: English
• Subjects: Fluid mechanics; Mixing; Non-Newtonian; PIV; Stirred tank; Viscoelastic
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2023.119301

Quantitative data on fluid dynamics in stirred tanks with viscoelastic fluids are scarcely available. Therefore, a particle image velocimetry study on flow phenomena occurring when agitating viscoelastic liquids with radial and axial impellers is presented. Different flow regimes exist, which result from interactions between elastic normal stresses and inertial forces: While for all agitators an axial pumping effect is found in the elastic regime, (semi-)radial flow patterns result in inertia-dominated flows. In the transition regime, locally limited zones exist dominated by either elasticity or inertia. This leads to a flow compartmentalization, a related pseudo-stagnation flow and reduced circulation rates. Which of the flow regimes is present can be predicted by the use of the elasticity number. With it, circulation flow numbers and flow distributions are standardized: In elastic flow conditions, these are constant. Thus, a scaling of the log-normally distributed velocities to the tip speed in this regime is possible. •Viscoelastic fluid flow quantified via PIV in a stirred tank for several impellers.•Flow reversal and compartmentalization occur with all analyzed impellers and fluids.•Categorization of flow regimes possible by the use of the elasticity number.•Unification of flow numbers and distributions by the use of the elasticity number.•Self-similarity of flows in the elastically dominated regime.