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Flow and mass transfer of fully resolved bubbles in non‐Newtonian fluids
Author(s) -
Radl Stefan,
Tryggvason Gretar,
Khinast Johannes G.
Publication year - 2007
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.11211
Subject(s) - viscoelasticity , mechanics , newtonian fluid , non newtonian fluid , shear thinning , generalized newtonian fluid , mass transfer , carreau fluid , coalescence (physics) , power law fluid , herschel–bulkley fluid , classical mechanics , bubble , rheology , advection , fluid dynamics , shear rate , physics , thermodynamics , astrobiology
In this work, high‐resolution 2‐D numerical simulations were performed on the motion of deformable bubbles in non‐Newtonian fluids and the associated mass transfer. For that purpose, we have implemented a semi‐Lagrangian advection scheme and improved the fluid dynamic calculation by the usage of implicit algorithms. Non‐Newtonian fluids are described by generalized Newtonian as well as viscoelastic model fluids. As shear‐thinning model we use a Power‐Law and a Carreau‐Yasuda model, the viscoelastic fluid simulations are based on an Upper‐Convected Maxwell model combined with a recently introduced model for the evolution of the effective shear rate. The mathematical challenges arising from the hyperbolic nature of the resulting set of equations are addressed by inclusion of artificial diffusion in the stress equation. In our work, it was found that shear thinning effects have impact on collision rates, and therefore, may influence coalescence of bubbles in non‐Newtonian liquids. Furthermore, for the first time, concentration fields of dissolved gas in viscoelastic fluids are presented. The study shows that the fluid elasticity plays a major role for bubble rise velocity, and therefore, mass transfer. As the wake dynamics differ significantly from that in Newtonian liquids, abnormal mixing characteristics can be expected in the bubbly flow of viscoelastic fluids. © 2007 American Institute of Chemical Engineers AIChE J, 2007