Paper Number
PO69 

Session
Poster Session

Title
Bubble rise in elastoviscoplastic materials

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. Spyridakis, Alexandros (University of Patras, Chemical Engineering)
2. Moschopoulos, Pantelis (University of Patras, Department of Chemical Engineering)
3. Varchanis, Stylianos (Okinawa Institute of Science and Technology)
4. Dimakopoulos, Yiannis (University of Patras, Department of Chemical Engineering)
5. Tsamopoulos, John (University of Patras, Department of Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Alexandros Spyridakis¹, Pantelis Moschopoulos¹, Stylianos Varchanis², Yiannis Dimakopoulos¹ and John Tsamopoulos^1
1Department of Chemical Engineering, University of Patras, Patras, Achaia 26225, Greece; ²Okinawa Institute of Science and Technology, Onna-son, Okinawa 904-0495, Japan

Speaker / Presenter 
Tsamopoulos, John

Keywords
computational methods; emulsions; foams; gels

Text of Abstract
The peculiar dynamics of bubbles rising in complex fluids has been studied extensively over the past decades. They are frequently encountered in industrial operations, and their presence can lead to undesirable consequences like mechanical degradation of the final product or safety issues. We undertake a novel computational study to examine the buoyancy-driven rise of a bubble in a yield stress fluid that is characterized both by elasticity and yield stress. The Saramito Herschel-Bulkley model [1] is used to model the rheological behavior of the material. The governing momentum and mass balance equations are solved numerically using the newly developed finite element method for free surfaces by Varchanis et al. [2], namely PEGAFEM-V. Furthermore, we assume axial symmetry, and that the center of the bubble volume remains at the origin of the coordinate system. For the first time, the bubble shape and the terminal velocity are in very good agreement with recent experimental data on Carbopol solutions. We analyze thoroughly the shear and normal stresses acting along the bubble surface because they provide insights into the underlying physical mechanisms. For smaller bubbles, large normal stresses arise in the trailing edge of the bubble due to the presence of elasticity, thus bubbles attain an inverted tear drop shape. Also, the negative wake structure appears behind the bubble. To our knowledge, it is the first time that these phenomena are accurately predicted in yield stress materials. However, for larger bubbles, inertia overcomes elasticity, and the bubble shape changes to that of an oblate ellipsoid or spherical cap. Moreover, we perform a parametric study varying the rheological properties of the material, i.e., the shear modulus and the consistency index. [1] P. Saramito. (2009). J. Non-Newtonian Fluid Mechanics: 158. [2] S. Varchanis, A. Syrakos, Y. Dimakopoulos, J. Tsamopoulos. (2020). J. Non-Newtonian Fluid Mechanics: 284.