We examine wave propagation on thin liquid films subjected to gravity, fluid friction, surface tension, and Marangoni effects. The physical configuration is a thin liquid layer on a planar incline. Following previous studies, the Marangoni effect is incorporated by a constant surface tension gradient and yields a non-convex flux function in our thin film equation. We extend previous studies by deriving the thin film equation governing two-dimensional waves on the liquid layer. We then derive a simplified evolution equation governing weakly nonlinear, quasi-planar, and weakly dissipative waves on the layer. When the undisturbed state is in the vicinity of an inflection point in the streamwise component of the flux function, the mixed nonlinearity, fourth order dissipation and the transverse modulations interact over time scales on the order of the scaled amplitude to the negative second power. The effect the transverse modulations is found to be intrinsically nonlinear. / Master of Science

abstract: Droplet-structure interactions play a pivotal role in many engineering applications as droplet-based solutions are evolving. This work explores the physical understanding of these interactions through systematic research leading to improvements in thermal management via dropwise condensation (DWC), and breathable protective wearables against chemical aerosols for better thermoregulation. In DWC, the heat transfer rate can be further increased by increasing the nucleation and by optimally ‘refreshing’ the surface via droplet shedding. Softening of surfaces favor the former while having an adverse effect on the latter. This optimization problem is addressed by investigating how mechanical properties of a substrate impact relevant droplet-surface interactions and DWC heat transfer rate. The results obtained by combining droplet induced surface deformation with finite element model show that softening of the substrates below a shear modulus of 500 kPa results in a significant reduction in the condensation heat transfer rate. On the other hand, interactions between droplet and polymer leading to polymer swelling can be used to develop breathable wearables for use in chemically harsh environments. Chemical aerosols are hazardous and conventional protective measures include impermeable barriers which limit the thermoregulation. To solve this, a solution is proposed consisting of a superabsorbent polymer developed to selectively absorb these chemicals and closing the pores in the fabric. Starting from understanding and modeling the droplet induced swelling in elastomers, the extent and topological characteristic of swelling is shown to depend on the relative comparison of the polymer and aerosol geometries. Then, this modeling is extended to a customized polymer, through a simplified characterization paradigm. In that, a new method is proposed to measure the swelling parameters of the polymer-solvent pair and develop a validated model for swelling. Through this study, it is shown that for this polymer, the concentration-dependent diffusion coefficient can be measured through gravimetry and Poroelastic Relaxation Indentation, simplifying the characterization effort. Finally, this model is used to design composite fabric. Specifically, using model results, the SAP geometry, base fabric design, method of composition is optimized, and the effectiveness of the composite fabric highlighted in moderate-to-high concentrations over short durations. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2019

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18053号 / 理博第3931号 / 新制||理||1567(附属図書館) / 30911 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)講師 市川 正敏, 教授 山本 潤, 教授 佐々 真一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24279号 / 理博第4877号 / 新制||理||1698(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)講師 市川 正敏, 教授 佐々 真一, 教授 山本 潤 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Laser lithography has been implemented in many ways to pattern polymeric materials. By using a tightly focused laser beam we can induce sharp thermal gradients, exceeding 1,500,000 °C/cm, onto the surface of a thin polymer film. The temperature dependence of the surface tension in such a thermal field gives rise to a flow of material away from the center of the beam focus driven by the Marangoni or thermocapillary effect. The evolution of a film irradiated by a focused laser can be, in a general sense, predicted by a presented hydrodynamic model, which is based on simple fluid mechanics. However, the details of the individual evolution profiles show a more complicated behaviour. It has been shown that this complex behaviour can be explained by considering the optical interference effects of the thin polymer coating. An optical feedback control routine has been developed to compensate for the interference effect by monitoring and maintaining a constant absorbed laser power. This ensures that the temperature gradient that drives the lithography process is consistent during operation. Additional studies involving high laser power effects, different material systems and other thin film phenomena have revealed an interesting assortment of novel behaviours. The extension of these behaviours to the lithography process lead towards the development of applications in microfabriation and microfluidic devices. / Thesis / Master of Applied Science (MASc)

No description available.

<p>The local corrosion of refractories at the slag/gas interface is a serious problem that limits the life of the refractories.Although, there have been several studies focused on understanding the Marangoni effect on the refractory dissolution process, there is little quantifiable analysis available. The aim of this study is to establish a better fundamental understanding of refractory dissolution mechanisms, and develop appropriate models for predicting the extent and rate of slag-line dissolution.</p> <p>In the first part of this research, experimental studies using a high temperature dip technique were performed: MgO refractory in SiO₂-CaO-FeO_x-MgO slag and Al₂O₃- SiO₂-CaO-FeO_x-MgO. The experiments were conducted at varies temperature. There was significant evidence of a spinel phase formed at the slag/refractory interface for slags containing 20wt.% Al₂O₃. This existence of the spinel seems to have retarded the dissolution of the refractory. The decrease in erosion rate in the presence of spinel is in proportion to the decrease in the equilibrium MgO concentration at the slag/solid interface. The activation energy is calculated from the relationship of effective mass transfer coefficient vs. temperature and found in the range of mass transfer activation energy.</p> <p>The second part of this search is developing a numerical model to predict the slag-line dissolution. An effective algorithm for analysis of unsteady Marangoni convection in refractory slag line dissolution has been developed. The results show that the Marangoni effect plays a very important role in slag-line erosion at this condition; both the moving boundary condition and curved surface condition have significant effects on the slag-line erosion rate. The comparison of experimental and numerical results shows that the model can predict the refractory maximum corrosion distance caused by Marangoni flow at the slag line. However, the eroded material volume was predicted within 20~30% deviation</p> / Doctor of Philosophy (PhD)

Beim Stoffübergang einer grenzflächenaktiven Substanz in einem flüssigen Zweiphasensystem kann solutale Marangoni-Instabilität einsetzen. Die weitere nichtlineare Entwicklung der Marangoni-Instabilität geht mit einer enormen Vielfalt von Strömungsmustern einher. In der Literatur wird dieser Aspekt häufig unter dem unscharfen Ausdruck „Grenzflächenturbulenz“ zusammengefasst. Diese Arbeit stellt heraus, dass drei grundlegende Strukturformen existieren: Rollzellen, Relaxationsoszillationen und Relaxationsoszillationswellen. Ein großer Teil der Komplexität der Strömungsmuster ist dadurch begründet, dass die Grundstrukturen unterschiedliche Hierarchieebenen aufweisen. Es werden die zugrunde liegenden Bedingungen für das Auftreten der jeweiligen Strukturtypen, ihre transiente Natur und die Bildung der hierarchischen Strömungsmuster untersucht. Des Weiteren betrachtet diese Arbeit die Wechselwirkungen mit Dichteeffekten, die sowohl die Charakteristik der Strukturen als auch ihre zeitliche Entwicklung beeinflussen.

<div>In many natural and industrial processes, bubbles are exposed to surface-active contaminants (surfactants) that may cover the whole or part of the bubble interface. A partial coverage of the bubble interface results in a spontaneous self-propulsion mechanism, which is yet poorly understood.</div><div>The main goal of this study is to enhance the understanding of the flow and interfacial mechanisms underlying the self-propulsion of small surfactant contaminated bubbles. The focus is on characterizing the self-propulsion regimes generated by the presence of surface-active species, and the influence of surfactant activity and surface coverage on the active bubble motion. </div><div>The study was developed by simultaneously solving the full system of partial differential equations governing the free-surface flow physics and the surfactant transport on the deforming bubble interface using multi-scale numerical simulation. </div><div>Results show in microscopic detail how surface tension gradients (Marangoni stresses) induced by the uneven interfacial coverage produce spontaneous hydrodynamics flows (Marangoni flows) on the surrounding liquid, leading to bubble motion. Results also establish the influence of both surfactant activity and interfacial coverage on total displacement and average bubble velocity at the macroscale. </div><div>Findings from this research improve the fundamental understanding of the free-surface dynamics of self-propulsion and the associated transport of surface-active species, which are critical to important natural and technological processes, ranging from the Marangoni propulsion of microorganisms to the active motion of bubbles and droplets in microfluidic devices. Overall, the findings advance our understanding of active matter behavior; that is, the behavior of material systems with members able to transduce surface energy and mass transport into active movement.</div>

Die vorliegende Arbeit behandelt Aspekte der Verschlackung von MgO in sekundärmetall-urgischen Schlacken. Mittels FactSage© wird eine Berechnung der Löslichkeit von MgO in Kalksilikat- und Kalkaluminatschlacke bei 1600, 1650 und 1700°C durchgeführt. Die Ergebnisse werden leicht handhab- und ablesbar dargestellt. Die Verschlackung eines porösen MgO-Probekörpers in einer an MgO ungesättigten und an MgO gesättigten Kalkaluminat-schlacke wird bei 1600°C thermogravimetrisch verfolgt. Der Verschlackungsvorgang wird maßgeblich durch die Mechanismen der Teilchendesintegration und Ostwald-Reifung in der infiltrierten Mikrostruktur beeinflusst. Das komplexe Zusammenspiel von Zerfall und Auflösung wird nach einem Modell von W. Gans an feuerfestes Material (MgO) angepasst und modelliert. Der Einfluss von Teilchendesintegration und Ostwald-Reifung auf den voreilenden Verschleiß im 3-Phasenkontakt (Marangoni-Konvektion) wird quantifiziert. Ferner wird ein einfaches Modell zur Abschätzung des voreilenden Verschleißes dargelegt.