De La Cruz-Araujo, Ronal A.

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    Model for the bouncing process of an air bubble interacting with an inclined wall
    (2011) De La Cruz-Araujo, Ronal A.; Cancelos, Silvina; College of Engineering; Gutierrez, Gustavo; Benitez, Jaime; Department of Mechanical Engineering; Canals, Miguel
    A model to predict the bouncing of an air bubble rising through an unbounded quiescent liquid and impinging on an inclined wall has been derived. This model is an extension to three dimensions of previous models in one and two dimensions based on the following methodology: Resolution of the bubble motion equation in an unbounded fluid in which an additional BubbleWall Interaction Force (BWIF) or often called the wall force is included to account for the excess pressure exerted in the fluid film between the wall and the top surface of the bubble when it approaches the wall. This force is obtained as the integral of the excess pressure calculated from the solution of the lubrication equation. In order to solve the resulting system of equations a numerical method was developed. This numerical method was a finite difference method in which the derivatives were approximated using a Taylor series expansion of second order accuracy. We have considered bubbles of diameter 0.3-2 mm which correspond to Reynolds numbers (Re) from 8 to 600 and Weber numbers (We) from 0.003 to 1.7. Re and We were calculated using the terminal velocity of the bubble. The numerical simulations predicted the bubble position during the bouncing process which was successfully validated with experimental data for the case of a horizontal wall. Also, the bubble velocity, deformation of the top surface of the bubble, excess pressure on the fluid film and the forces on the bubble were predicted. From the simulations results it was concluded that the bouncing process of a bubble is governed by the Reynolds Number, the Weber number and the wall inclination. For the case of a horizontal wall the model predicted the axisymmetry of the bubble deformation and excess pressure profile of the physical phenomenon. For the case of a wall with one inclination the results predicted asymmetrical behavior, which is consistent with previous experimental visualizations and model predictions. In the case of a wall inclined in two directions the bubble deformation and excess pressure profile were predicted asymmetrical in the two tangential directions. It was also observed that as the wall inclination increases the asymmetry increases and the rebound amplitude and the wall force decreases. The numerical simulations showed that the rebound of a deformable bubble against a wall is essentially governed by the balance between the wall force and added mass force in the normal direction to the wall, and the drag and the buoyancy forces in the tangential directions. Unlike previous three-dimensional numerical studies which were no able to predict bubble bounce on the wall; our model was able to compute several bubble bounces on an inclined wall with two angles. Moreover for the case of a horizontal wall the numerical results are in good agreement with experimental data.
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    Microstructure and rheology of Janus particle suspensions
    (2019-05-15) De La Cruz-Araujo, Ronal A.; Córdova Figueroa, Ubaldo M.; College of Engineering; Acevedo Rullán, Aldo; Cancelos, Silvina; Hernández Maldonado, Arturo J.; Department of Chemical Engineering; Pérez Muñoz, Fernando J.
    The aggregate sizes and morphologies formed with colloidal particles have important consequences on the rheological behavior of colloidal suspensions. Self- and directed-assembly are the most used phenomena to produce aggregates with controllable size and structure. On the other hand, the challenges focusing the actual technology requires better control and deep understanding of the aggregation phenomena at equilibrium and beyond it. Therefore, the design of colloidal particle interacting with anisotropic potentials—often known as Janus particles—arise as ideal candidates to advance in this direction. This dissertation sheds some light on the self- and directed-assembly of Janus particles suspensions with an introduction to the study of rheological properties of such systems through Brownian dynamics simulation. The colloidal particles are designed with amphiphilic, magnetic or catalytic Janus features subjected to a simple shear flow, a magnetic field, or to a single force (self-propulsion). Results show a richness structural behavior of Janus colloidal systems not observed with their isotropic counterparts. The different aggregate sizes and morphologies predicted as a function of interaction range, Janus patch size, interaction strength (i.e. Van Der Waals or magnetic interaction), shear rate, and self-propulsion strengths open new actuation routes for reconfigurable materials and applications.