Large eddy simulation of microbubble dispersion and flow field modulation in vertical channel flows

Abstract

Turbulent liquid–gas vertical channel flows laden with microbubbles are investigated using large eddy simulation (LES) two‐way coupled to a Lagrangian bubble tracking technique. Upward and downward flows at shear Reynolds numbers of Re τ = 150 and 590 are analyzed for three different microbubble diameters of 110, 220, and 330 μm. Predicted results are compared with published direct numerical simulation results although, with respect to comparable studies available in the literature, the range of bubble diameters and shear Reynolds numbers considered herein is extended to larger values. Microbubble concentration profiles are analyzed, with the microbubbles segregating at the wall in upflow conditions and moving toward the channel centre in downflow. The various forces acting on the bubbles, and the effect of the flow turbulence on the bubble concentration, are considered and quantified. Overall, the results suggest that the level of detail achievable with LES is sufficient to predict the fluid structures impacting bubble behavior. Therefore, LES coupled with Lagrangian bubble tracking shows promise for enabling the reliable prediction of bubble‐laden flows that are of industrial relevance. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1325–1339, 2019

Computational modeling of microbubble coalescence and breakup using large eddy simulation and Lagrangian tracking

“…The four‐way coupled model (two‐way coupled plus bubble collision, coalescence and breakup) was also applied to a vertical channel with the same geometrical dimensions as the horizontal case. As previously, for this case both single‐phase and two‐way coupled flows have been considered and validated in an earlier publication 20 to which the interested reader is referred. Starting from fully‐developed single‐phase solutions at Re τ = 150 and 590 in both upward and downward flow directions, microbubbles of diameter 110, 220 and 330 μm were injected into the flows, with the number of bubbles injected varied to give a void fraction of 0.1% in each flow.…”

“…The present work mainly focuses on the extension of the previous model to four‐way coupling (two‐way coupling plus bubble collision, coalescence and breakup) and associated results. Validation of the model has been previously obtained for single‐phase, one‐way and two‐way coupled simulations in both horizontal and vertical channels 20,36 …”

“…In the literature, most studies have focused on bubbles with diameters of a few millimeters, driven by the relevance of the bubbly flow regime during boiling and the role of bubble mixing in chemical, petrochemical and process engineering equipment such as bubble columns. However, more recently, attention has shifted to much smaller bubbles, having diameters of micro or even nanometers 20‐23 . Microbubbles are increasingly used in innovative applications such as the targeted delivery of drugs and anti‐tumor medicines in the human body 24,25 .…”

“…At the same time, the reduced computational effort that results from modeling, rather than simulating, the small‐scale turbulent fluctuations makes it possible to extend the methods' applicability to turbulent flows closer to conditions that are of industrial interest. In previous works, we have applied a similar approach to two‐way coupled horizontal, 36 and upward and downward vertical, channel flows, 20 addressing the interactions between the fluid and the microbubbles, and feedback of the bubbles to the turbulence in the fluid phase. In this work, the model is extended to four‐way coupled flows (two‐way coupled plus bubble collision, coalescence and breakup) by accounting for interactions between the bubbles, and bubble coalescence and breakup.…”

Single bubble breakup in the flow field induced by a horizontal jet—The numerical simulation

“…Chen et al used LES combined with VOF and discrete phase model to study the flow pattern and bubble distribution of air injection into water tank, where the influence of drag force and lift force on bubble motion was analyzed. Asiagbe et al simulated microbubbles in a vertical turbulent channel flow of water using LES, fluid structures affecting bubble behavior, and the influence of bubble on the continuous flow are obtained.…”