TitleAnalysis of dispersive mixing and breakup of air bubbles during continuous mixing of viscous liquids using experimental and numerical simulation techniques
NameVyakaranam, Kiran (author), Kokini, Jozef L (chair), HUANG, QINGRONG (internal member), Rogers, Michael A (internal member), Cuitino, Alberto (outside member), Rutgers University, Graduate School - New Brunswick,
Mixture distributions (Probability theory) ,
DescriptionAir bubble dispersion was studied during continuous mixing of a viscous Newtonian liquid in a Readco® 2” twin screw continuous mixer. A detailed review of fundamental bubble and drop breakup theories showed that elongation flows are needed for breakup of drops and bubbles in viscous flows. The velocity profiles and dispersive mixing ability of the twin screw mixer was analyzed using 3D Finite Element Method (FEM) simulations of flow and mixing and air bubble breakup was studied using experimental image analysis methods. Analysis of the velocity and pressure profiles showed that an introduction of paddle element stagger (forward or reverse) in a limited region of the mixing region caused variations in the local axial velocity. The axial transport happened mostly through the C-shaped region between the paddle elements and the barrel wall in the no stagger configuration and through the intermeshing region between the co-rotating paddle elements in a forward 45° stagger configuration. In case of a reverse 45° stagger configuration, significant local backflow regions were seen in the intermeshing region. A three region categorization was evident in the distribution of dispersive mixing index, with the highest values (predominantly elongation flow) occurring in the intermeshing region. It is proposed that the elongation flow in the intermeshing region occurred as a result of a squeeze flow created between the moving paddle element surfaces. The introduction of stagger disrupted this effect in and caused elongation flow intensity to be minimal in the intermeshing region. The measured bubble size distributions showed highest breakup for the no stagger configuration. A maximum stable bubble diameter predicted from local shear rates calculated from the FEM simulations in the mixer correlated well with the experimental mean bubble diameters. Effective shear rates calculated from measured mean bubble diameters were proportional to the mean shear rates calculated by the FEM simulations at various locations in the mixer for all paddle element configurations. This study provides methods to predict the effective shear rate for dispersion of air during continuous mixing of a highly viscous Newtonian liquid that can be applied to complex mixing flows.
NoteIncludes bibliographical references
Noteby Kiran Vyakaranam
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.