[PDF] Flow Structures In Bubbly Flows With A Tailored Bubble Size With And Without Liquid Co Flow eBook

Author : Aurore Loisy
Publisher :
Page : 0 pages
File Size : 25,11 MB
Release : 2016
Category :
ISBN :

GET BOOK

This thesis is devoted to the study of homogeneous bubbly flows and their coupling with scalar transport and turbulence. It focuses on the effects of finite size, hydrodynamic interactions, and suspension microstructure, which are investigated using direct numerical simulations at the bubble scale. The dynamics of laminar buoyancy-driven bubbly suspensions is first revisited. More specifically, the effect of volume fraction on the bubble drift velocity is clarified by connecting numerical results to theory for dilute ordered systems, and similarities between perfectly ordered and free disordered suspensions are evidenced. These results are then used for the modeling of passive scalar transport in laminar suspensions as described by an effective diffusivity tensor, and crucial differences between ordered and disordered systems with respect to scalar transport are highlighted. Lastly, turbulence is included in the simulations, and its interaction with a finite-size bubble is characterized. The behavior of a bubble as large as Taylor microscale is shown to share a number of common features with that of a microbubble, most notably, the flow sampled by the bubble is biased. A definition of the liquid flow seen by the bubble, as it enters in usual models for the added mass and the lift forces, is finally proposed.

Author : Michel Amasa Call
Publisher :
Page : 302 pages
File Size : 50,19 MB
Release : 2003
Category : Wakes (Fluid dynamics)
ISBN :

GET BOOK

"Much knowledge regarding the dynamics of rising bubbles' motion and their wakes has been gained from the investigations performed to date. The present study sought to add to this knowledge concerning the wake dynamics of a bubble in liquid flows by separately investigating the bubble tail's influence and the wall effect when the flow channel approaches a two-dimensional geometry."--Abstract, p. iii.

Author : Weibin Shi
Publisher :
Page : pages
File Size : 15,28 MB
Release : 2018
Category : Technology
ISBN :

GET BOOK

Bubble shapes have been assumed to be spherical in the currently available breakup models such as the one developed by Luo and Svendsen (1996). This particular breakup model has been widely accepted and implemented into CFD modelling of gas-liquid two-phase flows. However, simulation results obtained based on this model usually yield unreliable predictions about the breakage of very small bubbles. The incorporation of bubble shape variation into breakup models has rarely been documented in the study but the bubble shape plays an important role when considering the interactions with the surrounding turbulent eddies in turbulent bubbly flows, especially when the effects of bubble deformation, distortion and bubble internal pressure change are considered during the events of eddy-bubble collision. Thus, the assumption of spherical bubbles seems to be no longer appropriate in reflecting this phenomenon. This study proposes and implements an improved bubble breakup model, which accounts for the variation of bubble shapes when solving the population balance equations for CFD simulation of gas-liquid two-phase flows in bubble columns.

Author : Joseph Wakim
Publisher :
Page : 0 pages
File Size : 17,33 MB
Release : 2024
Category : Dissertations, Academic
ISBN :

GET BOOK

Understanding multiphase flows in bubble columns is crucial for various engineering applications. This study models a rectangular bubble column of laminar flow with a height of 2 meters and a width of 0.5 meters, where the inlet velocity of air is set at 3.3 mm/s. The simulations were done on Ansys Fluent using the mixture model, Volume of Fluid model and Eulerian model for two different numerical schemes, namely the first order upwind and the quadratic upstream interpolation for convective kinetics schemes. The mesh independence study demonstrated that in 2D simulations, mesh independence was achieved exclusively using the Eulerian model indicating that the Eulerian model is the most effective for simulating bubbly flow. Furthermore, when applying finer meshes in 3D simulations, the results closely aligned with the 2D simulations, supporting the validity of a 2D approach in the case of such flat bubble column. Additionally, finer meshes show thinner bubble swarms, particularly at the inlet. This study also investigated the impact of various parameters on bubble flow dynamics. It was found that the air inlet velocity, bubble sizes, and the properties of the working fluids significantly influenced the results. Specifically, as the air inlet velocity increased, the air volume fraction also increased. Conversely, increasing bubblesizes led to a decrease in both the air volume fraction and the water velocity, due to a reduced surface area to volume ratio. Moreover, changes in the working fluids showed that viscosity and density greatly affect the bubbly flow within the bubble column, highlighting the sensitivity of the system to these fluid properties.