Paper Number
PO68 

Session
Poster Session

Title
Buoyancy driven flow of deformable intrusions in elastoviscoplastic fluids

Presentation Date and Time
October 12, 2022 (Wednesday) 6:30

Track / Room
Poster Session / Riverwalk A

Authors (Click on name to view author profile)

1. Esposito, Giancarlo (University of Patras)
2. Moschopoulos, Pantelis (University of Patras, Department of Chemical Engineering)
3. Dimakopoulos, Yiannis (University of Patras, Department of Chemical Engineering)
4. Tsamopoulos, John (University of Patras, Department of Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Giancarlo Esposito¹, Pantelis Moschopoulos², Yiannis Dimakopoulos² and John Tsamopoulos^2
1University of Patras, Patras, Greece; ²Department of Chemical Engineering, University of Patras, Patras, Achaia 26225, Greece

Speaker / Presenter 
Tsamopoulos, John

Keywords
computational methods; emulsions; foams; gels

Text of Abstract
Multiphase systems containing liquid and gaseous intrusions, i.e. droplets and bubbles, are found in several formulation industries, ranging from the food sector to the pharmaceutical and construction ones. The interaction between the continuous phase and the deformable moving intrusion plays a critical role in the stability of complex emulsions and significantly impacts on the mechanical properties of the final product, therefore a careful examination is required. To this end, we perform a computational study to investigate the buoyancy driven motion of a single droplet, under the assumption of axial symmetry, in a yield stress material that exhibits both elastic and plastic effects. The rheological behaviour of the continuous phase is modelled via the Saramito Herschel-Bulkley constitutive equation, while the secondary phase is assumed to be Newtonian. The governing mass and momentum balance equations, coupled with the rheological model, are solved employing a Finite Volume Method formulation. To capture the interface between the two phases, the Volume of Fluid method is employed. The density and the viscosity of the dispersed phase are varied by several orders of magnitude, in order to describe the dynamics of bubbles (where the ratios approach to zero) and droplets. Initially, we validate our numerical setup in the context of a bubble rising, where quantitative agreement is found with respect to other numerical and experimental studies. Subsequently, we analyze the behaviour of a single rising droplet. The novel aspect of our work consists in the detailed analysis of the effect of the material properties on the flow conditions, including topological changes like breakup and coalescence of the dispersed phase. The effect of the viscosity ratio on the shape and the terminal velocity of the droplet is assessed to be pivotal and is found to be the critical parameter modulating both the occurrence and the type of breakup, i.e. tip streaming or large-droplets separation.