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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Study of nanosuspension droplets free evaporation and electrowetting

Orejon, Daniel January 2013 (has links)
Evaporation and wetting of droplets are a phenomena present in everyday life and in many industrial, biological or medical applications; thus controlling and understanding the underlying mechanisms governing this phenomena becomes of paramount importance. More recently, breakthroughs in the fabrication of new materials and nanomaterials have led to the synthesis of novel nanoscale particulates that dispersed into a base fluid modify the properties of this latter. Enhancement in heat transfer or the self-assembly of the particles in suspension during evaporation, are some of the areas in which nanofluids excel. Since it is a relatively new area of study, the interplay particle-particle, particle-fluid or particle-substrate at the macro-, micro-, and nanoscale is yet poorly understood. This work is an essay to elucidate the fundamental physics and mechanisms of these fluids during free evaporation, of great importance for the manipulation and precise control of the deposits. The evaporative behaviour of pure fluids on substrates varying in hydrophobicity has been studied and an unbalance Young’s force is proposed to explain the effect of substrate hydrophilicity on the pinning and the depinning forces involved during droplet evaporation. On other hand, the addition of nanoparticles to a base fluid modifies the evaporative behaviour of the latter and: a more marked “stick-slip” behaviour is observed when increasing concentration on hydrophobic substrates, besides the longer pinning of the contact line reported on hydrophilic ones when adding nanoparticles. A deposition theory to explain the final deposits observed, for the outermost ring, after the complete vanishing of a 0.1% TiO2-ethanol nanofluid droplet has also been developed. In addition, the evaporation of pinned nanofluid droplets on rough substrates at reduced pressures has been systematically studied. A revisited Young-Lippmann equation is proposed as one of the main findings to explain the enhancement on electrowetting performance of nanoparticle laden fluid droplets when compared to the pure fluid case. On the other hand, of relevant importance is the absence of “stick-slip” behaviour and the more homogeneous deposits found after the complete evaporation of a nanofluid droplet under an external electric field applied when compared to free evaporation of these fluids.
2

Nature-inspired systems exploiting porous media for multiphase flows

Umashankar, Viverjita 06 May 2020 (has links)
This thesis studies multi-phase flows within two different types of porous nature-inspired material systems: multi-layered feathers and synthetic trees. (1) How multilayered feathers enhance underwater superhydrophobicity. Inspired by ducks, here we demonstrate that air pockets can withstand up to five times more hydrostatic pressure when using stacked layers of synthetic feathers instead of a single layer. The mechanism for the multi-layered enhancement is the more tortuous pathway required for water impalement, which serves to pressurize the air pockets enclosed in the pores. We study this air compression effect using a probabilistic model, in which we quantify the tortuous pathway in stacked feather layers in terms of filled volume fraction of the pores. Our findings suggest that multi-layered coatings could enable robust underwater superhydrophobicity. (2) Oil-Water separation using synthetic trees. In the world's tallest trees, water evaporating from leaves generates enough suction to lift water over 100 m high. Transpiration can similarly be attained in synthetic trees by coupling nanoporous leaves" with conduits mimicking xylem capillaries. Here, we demonstrate that by adding filters to the free ends of the xylem conduits, the hydraulic load generated by transpiration can be used for oil-water separation. The working principle is illustrated using the pressure balance equation for the synthetic tree. / Master of Science / Nature abounds in complex systems and fascinating phenomena that have inspired us, from the way we live to the things we create. The engineering profession is no exception to being inspired by nature. In fact, engineers have created revolutinary robots inspired by animals. The work in this theis draws inspiration from the water-repellant property (superhydrophobicity) of duck feathers and the transpiration process in plants. In the first study, we created 'synthetic feathers' to study how layers of duck feathers are able to sustain superhydrophobicity under water. We discovered the 'layer-effect' that explains enhanced underwater superhydrophobicity. Surfaces covered in such multi-layered feather-like porous structures are potentially useful for reducing drag in underwater applications. In the second study, we develop a 'synthetic tree' that captures the main attributes of the transpiration mechanism in plants. We show that the 'pull' generated by transpiration can be used for oil-water separation. This macroscopic synthetic tree can be useful in cleaning oil spills.
3

Design Principles for the Cathode/Electrolyte Interfacial Phenomena in Lithium Ion Batteries / リチウムイオン二次電池正極/電解質界面構造の解明と設計

Yamamoto, Kentarou 23 March 2015 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(人間・環境学) / 甲第19072号 / 人博第725号 / 新制||人||174(附属図書館) / 26||人博||725(吉田南総合図書館) / 32023 / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 内本 喜晴, 教授 加藤 立久, 教授 吉田 寿雄 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DGAM
4

Leveraging Capillarity

Murphy, Kevin Robert 20 September 2022 (has links)
Surface tension is an essential force for the functioning of the world and life. Centuries of study, and still, new applications and limits of surface tension are being explored. Water has always drawn attention for its high surface tension value, 72mN/m compared to ethanol's 20mN/m. The high surface tension allows for numerous applications, superhydrophobic surfaces being one that takes heavy advantage of that value. Superhydrophobicsurfaceshave a high surface energy cost with water, resulting in small contact areas with high advancing and receding contact angles and low contact angle hysteresis. This results in very low adhesion on the surfaces. Here we study the ability of superhydrophobic surfaces with their low adhesion to shed meltwater from frost, showing a decrease in frost thickness to below 3mm for the meltwater to shed. We then take another approach to removing water from a surface, rather than increasing the surface energy cost, we introduce a difference in surface energy cost. Introducing a porous surface across from a solid one, droplets transfer from the solid to the porous, removing over 90% of the volume of the droplet from the solid surface. We thoroughly examine and model the hydrodynamics of the transfer process, varying the solid surface, the donor surface, and the liquid. This bridging between surfaces is then applied to fog harps, examining the efficiencies of large-form fog harps. Fog harps have shown a 3 to 5 times increase in water collection compared to the industry-standard mesh collector. However, droplets from fog collected on the wires eventually grow large enough to touch neighboring wires. Tominimizetheirsurfaceenergy, they begin pulling wires together, "tangling" them. This can potentially reduce efficiency, but has not been applied to large-scale harps until here. Another application of surface tension is then examined, using lower surface tension oils, but trapping them in microstructures to make slippery liquid-infused porous surfaces (SLIPS). The oil coats the microstructure, due to its lower surface tension. This creates a lubricating layer on the surface, along with potential air pockets reducing friction further. These surfaces have been studied extensively with liquids being placed on them, but here we begin to examine them when solids are used instead, showing some interesting cases where increasing the viscosity of the oil actually decreases the friction force. / Doctor of Philosophy / Sponges are something everyone has used, and most people can tell you that they work using surface tension. And for most people, that's enough. It's actually more useful to know to squeeze your sponge dry when you're done to prevent mold than it is to know that it holds onto liquids because of surface tension. But the point here was to take the study of sponges and surface tension to the extreme. To the point that some knowledge is going to be gained solely for the sake of gaining knowledge. Not all knowledge will have immediate uses, but this doesn't take value away from the knowledge, or any eventual uses it might have. So we start this by looking at the building of scientific knowledge and noticing that a brick is missing. Superhydrophobic surfaces, surfaces that water doesn't want to touch, have been studied very extensively and their properties have been thoroughly explored. However, a direct comparison of the defrosting behaviors, the process of frost melting on a surface, between superhydrophobic and hydrophobic surfaces had not been done. Water does prefer to be on a hydrophobic surface compared to a superhydrophobic one, but it's still uncomfortable. A plate was treated so that half was hydrophobic and the other half was superhydrophobic. Frost was grown across the surface and then melted simultaneously, allowing us to characterize the differences in the behaviors, highlighting the ability of the superhydrophobic surface to shed water droplets at smaller sizes than other surfaces. Next is a pure fluid mechanics work supporting a heat transfer application. Evaporation, for enhanced heat transfer, and a hydrophilic wick, essentially a sponge, are paired to create a plate with one-way heat transfer. Heating side A can heat side B, but heating side B can't heat side A. Water in the wick gets heated, evaporates from side A and then condenses on side B, carrying heat with it. The condensation grows until it touches the wick, which then pulls it in, allowing it to be evaporated again and cycling more heat. When side B, the smooth surface, is heated, the water can evaporate off it and condense in the wick, but then it has no way to return, preventing further heat transfer. The process of droplets being pulled from side B to the wick in side A is key to the process. It's a sponge pulling water in using surface tension. However, all the smaller pieces have been taken for granted. The second piece is a systematic study of this capture mechanism, exploring the effects of changing liquids, donor surfaces, and receiving porous wicks. The third is a continuation of the lab's previous work on Fog Harps, arrays of vertical fibers held in place to let fog run into them. The droplets grow until they slide down and can be collected. The wires of the harp are close enough that the water can actually start to tangle them together. This tangling can increase the water needed for sliding and collection to begin. Tensioning the wires can help mitigate the tangling. Here we show harps on around 1,$text{m}^2$, using optimal wire size and spacing that is possible for mass manufacturing. The harps were tested in the lab using humidifiers to generate fog for the harps to collect. Finally, an initial study of solid objects being pulled across oil-infused microstructured surfaces. The microstructure helps keep the oil on the surface thanks to the surface energy of the oil. These oil-infused surfaces have been studied extensively when liquids are placed on them, but not with solid objects. Solid objects can exert significantly more pressure than liquids, which naturally want to spread when they reach a certain thickness. Experiments were performed with a variety of oil viscosities, microstructures, and oil excess thicknesses. This work is not entirely complete but a significant portion of it is presented here.
5

Nanoscale Transport of Multicomponent Fluids in Shales

Zhang, Hongwei 02 January 2025 (has links)
CO2 injection has demonstrated significant potential for enhanced oil recovery techniques in unconventional reservoirs, but there exists many challenges in optimizing its operations due to the limited understanding of CO2-oil transport mechanisms in these systems. This dissertation addresses these challenges using molecular dynamics (MD) simulations by investigating the gas and oil transport behaviors and properties within single nanopores under reservoir conditions. The first study examines the exchange dynamics of decane with CO2 and CH4 in a 4 nm-wide calcite nanopore. It is shown that both gases form distinct adsorbed and free molecular populations upon entering the pores, leading to different extraction dynamics. Notably, CO2-decane exchange is initially driven by adsorbed populations, with a transition to free populations later; whereas CH4 -decane exchange follows the opposite pattern. Despite these differences, the transport of both gases apparently follows the same diffusive behavior, with CH4 exhibiting higher effective diffusivities. By calculating self-diffusivities at various relevant compositions, it is found they do not always align well with their effective diffusivities. The second study therefore focuses on Maxwell-Stefan (M-S) diffusivities as a more comprehensive framework to describe the diffusion of CO2-decane mixtures in the first study. It is found that D12 (CO2-decane interactions) remains relatively constant across compositions, unlike bulk mixtures, while D1,s (CO2-wall interactions) increases sharply with CO2 loading. In contrast, D2,s (decane-wall interactions) shows a nonmonotonic trend and, unexpectedly, becomes negative under certain compositions. These phenomena are linked to the strong adsorption of CO2, causing significant density heterogeneity and reduced mobility. Using a multi-task Gaussian process regression model, the M−S diffusivities can be predicted with a relative root mean square error below 10%, significantly reducing computational demand for their practical usage. The third study examines concentration gradient driven diffusio-osmosis of oil-CO2 mixtures within silica and calcite nanopores. Despite higher CO2 enrichment near calcite walls, diffusio-osmotic is only marginally stronger than in silica pores, which is attributed to the variations in interfacial fluid structures and hydrodynamic properties in different pores. Continuum simulations suggest that diffusio-osmosis becomes increasingly significant compared to Poiseuille flow as pore width decreases. The fourth study investigates the oil mixture (C10+C19) recovery from a 4 nm-wide calcite dead-end pore with and without CO2 injection. It was found that CO2 accelerates oil recovery and reduces selectivity for lighter components (e.g., C10) compared to the recovery without CO2. Such improvements are influenced by interfacial and bulk phenomena, including adsorption competition and solubilization effects. Together, these studies provide quantitative insights into CO2-oil transport mechanisms and properties in nanopores. Such insights can help develop better reservoir simulators to guide the optimization of CO2 injection-based enhanced oil recovery in unconventional reservoirs. / Doctor of Philosophy / Recovering oil from unconventional reservoirs—types of underground rock formations that trap oil in extremely tiny pores, much smaller than the thickness of a strand of hair—is one of the biggest challenges in the petroleum industry. The narrow pore size greatly increases the fraction of the oil flow, and many pores are not even connected, which stops oil to flow out on its own, making it much harder to extract from these reservoirs. Injecting gases into the reservoirs, like carbon dioxide (CO2), has become a promising solution. This method not only helps to push the oil out but also allows part of the injected CO2 to be stored underground, reducing its impact on the atmosphere. To make this process work better, we need in depth understandings of how oil and gas move in these tiny rock spaces. Four studies have been conducted to elucidate the transport phenomena in CO2 injection-based enhanced oil recovery. The first study finds that the exchange between trapped oil and CO2 is significantly influenced by how oil and CO2 stick to the walls of these tiny pores. However, it is observed that commonly used characterization methods do not always work well in the prediction of recovery behavior, indicating the need for a better framework to describe this process. To address this problem, we have brought up a new framework in the second study, which considers both the interactions between oil and CO2 and the interactions with the pore wall. Given the high computational costs, a machine learning model is trained with the data collected to make future predictions faster and cheaper. The third study quantifies the strength of a new type of flow. This flow can be comparable in magnitude to pressure difference-driven flow in tiny pores. Lastly, the recovery of an oil mixture composed of light and heavy hydrocarbons is explored. It was discovered that gas injection not only increases the overall oil recovery rate but also decreases the selectivity toward lighter hydrocarbons. These discoveries pave the way for improved models and strategies to optimize the gas injection process to recover oil from these challenging reservoirs, ultimately meeting the energy needs while supporting efforts to reduce atmospheric CO2 levels.
6

Colloidal interfaces in confinement

Jamie, Elizabeth A. G. January 2011 (has links)
A fluid-fluid demixing colloid-polymer system provides us with an opportunity to study interfacial phenomena that cannot be observed in molecular systems due to unfavourable length and timescales. We develop such a system compatible with cells of varying dimensions, allowing us to investigate confined interfacial behaviour in real space using Confocal Scanning Laser Microscopy. The degree to which a system is affected by the sedimentation-diffusion gradient is dependent on the ratio of the suspension height to the gravitational length of the colloids. We illustrate that we may control the distance of our interface to the critical point by altering the suspension height, determining the importance of the gravitational field. Furthermore, the timescale on which the sedimentation- diffusion gradient is established is considerably longer than that of initial fluid-fluid demixing. We show that after the formation of the macroscopic interface, the system passes through a series of local mechanical equilibria on the way to achieving full equilibrium. Should the system be of sufficient height, it will pass through the gas-liquid critical point opening up new ways to study critical phenomena. The time and length scales of the fluid-fluid demixing of our system may be manipulated by altering the density and viscosity of our solvent. We exploit a slowed phase separation process to study the interplay between demixing and wetting phenomena of systems in the vicinity of a single wetting surface, and confined between two parallel plates. We demonstrate that the presence of a surface strongly affects the morphology of phase separation. The growth of the wetting layer is determined by the demixing regime of the system, and may be accelerated by hydrodynamics. The additional restriction by a second surface limits the lengthscale of coarsening domains and may further alter the mechanism of wetting layer growth.
7

Thermophoresis in colloidal suspensions

Burelbach, Jérôme January 2018 (has links)
This dissertation examines the motion of colloids in a temperature gradient, a non-equilibrium phenomenon also known as thermophoresis. Chapter 1 gives an introduction to the existing applications and basic concepts of thermophoresis and outlines some of the experimental and theoretical challenges that serve as a motivation for this PhD project. In Chapter 2, a general theoretical description for thermophoresis is formulated using the theory of non-equilibrium thermodynamics. The colloidal flux is split up into an interfacial single-colloid contribution and a bulk contribution, followed by a determination of transport coefficients based on Onsager’s reciprocal relations. It is further shown how the phenomenological expression of the thermophoretic flux can be recovered when the fluid is at steady-state. The results issuing from this description are then discussed and compared to other existing approaches, some of which are shown to neglect the hydrodynamic character of colloidal thermophoresis. Chapter 3 is dedicated to the validation of the introduced theoretical framework by means of computer simulations, using a simulation technique known as multi-particle collision dynamics. More specifically, the dependence of the thermophoretic force on different system parameters is examined and deviations from the theoretical prediction are explained by an advective distortion of interfacial fluid properties at the colloidal surface. Chapter 4 presents steady-state measurements of functionalised colloids in a temperature gradient, showing how the addition of molecular surface groups increases the experimental complexity of thermophoretic motion. The relaxation process behind this steady-state is also studied, to determine how the relaxation speed depends on the applied temperature gradient. In chapter 5, a general conclusion is drawn from the presented work and its implications are briefly discussed in relation to the current state of knowledge. Finally, the discussion is closed with an outlook on remaining challenges in understanding colloidal motion that could be the subject of future research.
8

Hierarchical spatiotemporal analyses and the design of all-solid-state lithium-ion batteries / 階層的時空間解析と全固体リチウムイオン電池の設計

Yang, Seunghoon 25 July 2022 (has links)
京都大学 / 新制・課程博士 / 博士(人間・環境学) / 甲第24149号 / 人博第1052号 / 新制||人||246(附属図書館) / 2022||人博||1052(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 内本 喜晴, 教授 吉田 鉄平, 准教授 松井 敏明, 教授 林 晃敏 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM
9

COMPLEX FLUIDS IN ENERGY GEO-ENGINEERING

Benitez, Marcelo 29 August 2023 (has links)
The energy demand has increased dramatically in the last century, and so to have global CO2 emissions. Two critical challenges for the geo-energy sector are to develop different approaches for harvesting energy and to actively decrease atmospheric CO2 emissions. Addressing these challenges requires efficient, sustainable, and affordable technical solutions. Complex fluids are ubiquitous and offer great potential for geo-engineering applications such as the development of geo-energy, enhanced oil recovery and CO2 geological sequestration and utilization. This thesis will present new results on interfacial phenomena in CO2-fluid-mineral systems, including interfacial tension hysteresis, the effects of surface-active components on interfacial tension (surfactants, nanoparticles, organo-bentonites and asphaltenes), and the interfacial pinning of immiscible fluids on substrates. Pore-scale phenomena come together in the study of the physical properties of CO2 and its implication for both storage and assisted gravity oil drainage. Finally, we provide a better understanding of the interfacial phenomena of complex fluids and their interactions within porous media that can lead to efficient and sustainable geo-energy systems.
10

Surface characterization of carbon fibers and interfacial phenomena in carbon reinforced composites

Sellitti, Claudio January 1990 (has links)
No description available.

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