A Multiscale Approach for Modeling Bubbles Rising in Non-Newtonian Fluids

Abstract

The present work reports a multiscale approach to describe the dynamics of a chain of bubbles rising in non-Newtonian fluids. By means of the particle image velocimetry (PIV) and the lattice Boltzmann (LB) simulation, a deep understanding of the complex flow pattern around a single bubble is gained at microscale. The interactions and coalescences between bubbles rising in non-Newtonian fluids are experimentally investigated by the PIV measurements, birefringence, and rheological characterization for both an isolated bubble and a chain of bubbles formed from a submerged orifice. Two aspects are identified as central to interactions and coalescence: the stress creation by the passage of bubbles and their relaxation due to the fluid’s memory. This competition between the creation and relaxation of stresses displays nonlinear complex dynamics. Along with the detailed knowledge around a single bubble, these fundamental mechanisms governing the bubbles’ collective behavior in a train of bubbles at mesoscale leads to cognitive modeling on the basis of behavioral rules. By simulating bubbles as adaptive agents with the surrounding fluid via averaged residual stresses, model predictions for consecutive coalescence between a great number of bubbles compare very satisfactorily with the experimental investigation at macroscale.

On the velocity discontinuity at a critical volume of a bubble rising in a viscoelastic fluid

“…The numerical difficulties that exist due to the complex physics of the free surface, coupled with the hyperbolic character of the constitutive equations used to describe the elastic properties of the material, did not allow the theoretical studies to proceed to the accurate reproduction of the experimentally observed 'velocity jump'. Additionally, no reported results exist for the stationary solutions, which could lie in the discontinuous region because the problem is approached using transient simulations only (Wagner, Giraud & Scott 2000;Malaga & Rallison 2007;Pillapakkam et al 2007;Frank et al 2012). There are still many open questions on the origin of the velocity jump.…”

Systematic Study on the Coalescence and Breakup Behaviors of Multiple Parallel Bubbles Rising in Power-law Fluid

“…The knowledge of parallel bubble coalescence and breakup could increase the predictability of gas–liquid equipment design as well as improve the understanding of the mechanisms of bubble coalescence and interaction systematically. The information about interactions and coalescence between parallel bubbles is also required for the multiscale modeling approach. , In this article, coalescence and breakup processes of multiple parallel bubbles in power-law fluid were studied systematically using VOF method, the critical bubble intervals for bubble coalescence were obtained for different bubble numbers and rheological properties, different regimes of multiple bubbles coalescence were classified according to dimensionless numbers, and the mechanisms of parallel bubble coalescence and breakup were analyzed.…”

A numerical approach for non-Newtonian two-phase flows using a conservative level-set method

“…They used this new approach to simulate a bubble rising in a viscoelastic fluid and were able to reproduce the experimentally observed cusp shape at the trailing end of the bubble. Frank et al [24] presented a multiscale approach to describe the dynamics of a chain of bubbles rising in non-Newtonian fluids using the particle image velocimetry (PIV) and the LBM simulations.…”