Computational analysis of single rising bubbles influenced by soluble surfactant

This paper presents novel insights about the influence of soluble surfactants on bubble flows obtained by Direct Numerical Simulation (DNS). Surfactants are amphiphilic compounds which accumulate at fluid interfaces and significantly modify the respective interfacial properties, influencing also the overall dynamics of the flow. With the aid of DNS local quantities like the surfactant distribution on the bubble surface can be accessed for a better understanding of the physical phenomena occurring close to the interface. The core part of the physical model consists in the description of the surfactant transport in the bulk and on the deformable interface. The solution procedure is based on an Arbitrary Lagrangian-Eulerian (ALE) Interface-Tracking method. The existing methodology was enhanced to describe a wider range of physical phenomena. A subgrid-scale (SGS) model is employed in the cases where a fully resolved DNS for the species transport is not feasible due to high mesh resolution requirements and, therefore, high computational costs. After an exhaustive validation of the latest numerical developments, the DNS of single rising bubbles in contaminated solutions is compared to experimental results. The full velocity transients of the rising bubbles, especially the contaminated ones, are correctly reproduced by the DNS. The simulation results are then studied to gain a better understanding of the local bubble dynamics under the effect of soluble surfactant. One of the main insights is that the quasi-steady state of the rise velocity is reached without ad- and desorption being necessarily in local equilibrium

Drop coalescence in technical liquid/liquid applications : a review on experimental techniques and modeling approaches

The coalescence phenomenon of drops in liquid/liquid systems is reviewed with particular focus on its technical relevance and application. Due to the complexity of coalescence, a comprehensive survey of the coalescence process and the numerous influencing factors is given. Subsequently, available experimental techniques with different levels of detail are summarized and compared. These techniques can be divided in simple settling tests for qualitative coalescence behavior investigations and gravity settler design, single-drop coalescence studies at flat interfaces as well as between droplets, and detailed film drainage analysis. To model the coalescence rate in liquid/liquid systems on a technical scale, the generic population balance framework is introduced. Additionally, different coalescence modeling approaches are reviewed with ascending level of detail from empirical correlations to comprehensive film drainage models and detailed computational fluid and particle dynamics

6th International congress of the Serbian society of mechanics: Review

Ovaj rad prikazuje najvažnije informacije o 6. kongresu Srpskog društva za mehaniku, koji je održan na Tari od 19. do 21. juna 2017. Kongres je organizovan od strane Srpskog društva za mehaniku. Dat je kratak prikaz najznačajnijih radova predstavljenih na ovom kongresu, a koji se bave teorijskom i primenjenom mehanikom.This paper presents the most important information and describes the activities of the 6th Congress of the Serbian Society of Mechanics which was held on mountain Tara, on 19- 21 June, 2017. The Congress was organized by the Serbian Society of Mechanics. Brief summaries of the plenary lectures and some of 99 accepted papers, which admittedly attracted the most interest were shown as well

6th International congress of the Serbian society of mechanics: Review

Ovaj rad prikazuje najvažnije informacije o 6. kongresu Srpskog društva za mehaniku, koji je održan na Tari od 19. do 21. juna 2017. Kongres je organizovan od strane Srpskog društva za mehaniku. Dat je kratak prikaz najznačajnijih radova predstavljenih na ovom kongresu, a koji se bave teorijskom i primenjenom mehanikom.This paper presents the most important information and describes the activities of the 6th Congress of the Serbian Society of Mechanics which was held on mountain Tara, on 19- 21 June, 2017. The Congress was organized by the Serbian Society of Mechanics. Brief summaries of the plenary lectures and some of 99 accepted papers, which admittedly attracted the most interest were shown as well

Microfluidics for assessing the behaviour of deformable biological objects

Biological fluids, composed of polymeric solutions or suspensions of deformable particles, commonly present complex rheological behaviour. It is well known that particle-fluid interactions at the microscale dictate the macroscopic flow behaviour of these fluids, however the exact link in numerous situations is still missing. Recently, microfluidic techniques have been widely employed to study the dynamics of microscopic particles under flow.;Even though such techniques present a range of advantages, including the precise control of the flow conditions, as well as the consumption of a small amount of sample, the design of the microfluidic geometries still mostly relies on a trial-and-error approach. In this thesis, we experimentally test a set of microfluidic geometries, the design of which was previously optimised based on theoretical considerations or by means of numerical simulations in order to achieve specific flow conditions.;In addition, we have used complex observation techniques to study the dynamics of solutions and suspensions under flow, identifying microscopic dynamics as well as the major limitations of the microfluidic devices. Biological fluids such as solutions of DNA molecules and red blood cells suspensions were investigated in shear-dominated and extension-dominated flows and the performance of the optimised flow geometries for the study of such biological fluids was demonstrated.Biological fluids, composed of polymeric solutions or suspensions of deformable particles, commonly present complex rheological behaviour. It is well known that particle-fluid interactions at the microscale dictate the macroscopic flow behaviour of these fluids, however the exact link in numerous situations is still missing. Recently, microfluidic techniques have been widely employed to study the dynamics of microscopic particles under flow.;Even though such techniques present a range of advantages, including the precise control of the flow conditions, as well as the consumption of a small amount of sample, the design of the microfluidic geometries still mostly relies on a trial-and-error approach. In this thesis, we experimentally test a set of microfluidic geometries, the design of which was previously optimised based on theoretical considerations or by means of numerical simulations in order to achieve specific flow conditions.;In addition, we have used complex observation techniques to study the dynamics of solutions and suspensions under flow, identifying microscopic dynamics as well as the major limitations of the microfluidic devices. Biological fluids such as solutions of DNA molecules and red blood cells suspensions were investigated in shear-dominated and extension-dominated flows and the performance of the optimised flow geometries for the study of such biological fluids was demonstrated