Abstract Argon-oxygen decarburisation (AOD) is the most common unit process for refining stainless steel. The AOD process consists of multiple stages, in which the rate of processing is determined by complex reaction mechanisms. The main objective of this work was to study the chemical rate phenomena in selected process stages. For this purpose, an extensive literature review was conducted to clarify the main assumptions of the existing reaction models. Based on the literature review, a new categorisation of the models was proposed. In addition, a literature review was conducted to identify the main phenomena that affect the reaction kinetics in the AOD process. In this work, based on the law of mass action, a novel kinetic approach and its application for modelling of parallel mass transfer controlled reactions were studied. The developed approach enables the simultaneous solution of the chemical equilibrium and mass transfer rate which controls it. A simplified reaction model was employed for studying the effect of mass transfer rates and residual affinity on the constrained equilibrium at the reaction interface. An earlier-proposed AOD model was extended with two phenomenon-based sub-models. The top-blowing model is based on the assumption that reactions take place simultaneously at the surface of the cavity formed by the momentum of the gas jet and on the surface of the metal droplets caused by the shear force of the gas jet. The reduction model describes the reactions during the reduction stage of the AOD process by assuming that all reactions take place between the metal bath and emulsified slag droplets. The results obtained with the models were in good agreement with the measurement data collected from a steel plant. Owing to their phenomenon-based structure, the developed models are well-suited for the analysis of both existing and new production practices. / Tiivistelmä Argon-happimellotus (AOD) on yleisin ruostumattoman teräksen valmistamiseen käytettävä yksikköprosessi. AOD-prosessi koostuu useista vaiheista, joissa prosessointinopeutta määrittävät monimutkaiset reaktiomekanismit. Tutkimuksen päätavoitteena oli tutkia kemiallisia nopeusilmiöitä valituissa prosessivaiheissa. Tähän liittyen tehtiin kattava kirjallisuuskatsaus, jonka tavoitteena oli tunnistaa olemassa olevien reaktiomallien pääoletukset. Kirjallisuuskatsauksen pohjalta esitettiin uusi mallien kategorisointi. Lisäksi tehtiin kirjallisuuskatsaus, jonka tavoitteena oli tunnistaa tärkeimmät reaktiokinetiikkaan vaikuttavat ilmiöt AOD-prosessissa. Tässä työssä tutkittiin uudenlaista massavaikutuksen lakiin perustuvaa lähestymistapaa sekä sen soveltamista rinnakkaisten aineensiirron rajoittamien reaktioiden mallinnukseen. Kehitetty lähestymistapa mahdollistaa kemiallisen tasapainotilan sekä sitä rajoittavan aineensiirron samanaikaisen ratkaisun. Aineensiirtonopeuksien ja jäännösaffiniteetin vaikutusta reaktiopinnalla vallitsevaan rajoitettuun tasapainotilaan tutkittiin käyttämällä yksinkertaistettua reaktiomallia. Aiemmin kehitettyä AOD-mallia laajennettiin kahdella ilmiöpohjaisella alimallilla. Lanssipuhallusmalli perustuu oletukseen, että reaktiot tapahtuvat samanaikaisesti kaasusuihkun liikemäärän muodostaman tunkeuman ja kaasusuihkun leikkausvoiman aiheuttamien metallipisaroiden pinnalla. Pelkistysmalli kuvaa AOD-prosessin pelkistysvaiheen aikana tapahtuvia reaktioita olettaen, että kaikki reaktiot tapahtuvat terässulan ja emulgoituneiden kuonapisaroiden välillä. Malleilla saadut tulokset vastasivat hyvin terästehtaalta kerättyä mittausaineistoa. Ilmiöpohjaisen rakenteensa ansiosta kehitetyt mallit soveltuvat hyvin sekä olemassa olevien että uusien tuotantopraktiikoiden analysoimiseen.

Selectively permeable biological membranes composed of lipophilic barriers inspire the design of biomimetic carrier-mediated membranes for aqueous solute separation. This work imparts selective permeability to lipid-filled pores of silica thin film composite membranes using carrier molecules that reside in the lipophilic self-assemblies. The lipids confined inside the pores of silica are proven to be a more effective barrier than bilayers formed on the porous surface through vesicle fusion, which is critical for quantifying the function of an immobilized carrier. The ability of a lipophilic carrier embedded in the lipid bilayer to reversibly bind the target solute and transport it through the membrane is demonstrated. Through the functionalization of the silica surface with enzymes, enzymatic catalysis and biomimetic separations can be combined on this nanostructured composite platform. The successful development of biomimetic nanocomposite membrane can provide for efficient dilute aqueous solute upgrading or separations using engineered carrier/catalyst/support systems. While the carrier-mediated biomimetic membranes hold great potential, fully understanding of the transport processes in composite synthetic membranes is essential for improve the membrane performance. Electrochemical impedance spectroscopy (EIS) technique is demonstrated to be a useful tool for characterizing the thin film pore accessibility. Furthermore, the effect of lipid bilayer preparation methods on the silica thin film (in the form of pore enveloping, pore filling) on ion transport is explored, as a lipid bilayer with high electrically insulation is essential for detecting activity of proteins or biomimetic carriers in the bilayer. This study provides insights for making better barriers on mesoporous support for carrier-mediated membrane separation process. Porous silica nanoparticles (pSNPs) with pore sizes appropriate for biomolecule loading are potential for encapsulating dsRNA within the pores to achieve effective delivery of dsRNA to insects for RNA interference (RNAi). The mobility of dsRNA in the nanopores of the pSNPs is expected to have a functional effect on delivery of dsRNA to insects. The importance of pores to a mobile dsRNA network is demonstrated by the lack of measurable mobility for both lengths of RNA on nonporous materials. In addition, when the dsRNA could not penetrate the pores, dsRNA mobility is also not measurable at the surface of the particle. Thus, the pores seem to serve as a “sink” in providing a mobile network of dsRNA on the surface of the particle. This work successfully demonstrates the loading of RNA on functionalized pSNPs and identified factors that affects RNA loading and releasing, which provides basis for the delivery of RNA-loaded silica particles in vivo.

One of the most promising routes to renewable liquid fuels and chemicals is the fermentation of waste carbon by specialized microbes. Commercial development of gas fermentation technology is underway but many fundamental research problems must be addressed to further advance the technology towards economic competitiveness. This thesis addresses the important problem of developing integrated metabolic and transport models that predict gas fermentation performance in industrially relevant bubble column reactors. The computational models describe the conversion of CO-rich waste streams including synthesis gas to the platform chemical butyrate. The proposed modeling approach involves combining genome-scale reconstructions of bacterial species metabolism with transport equations that govern the relevant multiphase convective and diffusional processes within the spatially-varying system. I compared the combination of the acetogen Clostridium autoethanogenum for CO conversion to the intermediate acetate and three different gut bacteria (Clostridium hylemonae, Eubacterium rectale and Roseburia hominis) for conversion of acetate to butyrate. Trial-and-error optimization of the three co-culture designs was performed to assess their relative performance and guide future experimental studies.

<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>

Capillarity is often exploited in self-cleaning, drag reducing and fluid absorption/storage (sanitary products) purposes just to name a few. Formulating the underlying physics of capillarity helps future design and development of optimized structures. This work reports on developing computational models to quantify the capillary pressure and capillary forces on the fibrous surfaces. To this end, the current study utilizes a novel mass-spring-damper approach to incorporate the mechanical properties of the fibers in generating virtual fibrous structures that can best represent fibrous membranes. Such virtual fibrous structures are then subjected to a pressure estimation model, developed for the first time in this work, to estimate the liquid entry pressure (LEP) for a hydrophobic fibrous membrane. As for accurate prediction (and not just estimation) of the capillary pressure, this work also presents an energy minimization method, implemented in the Surface Evolver code, for tracking the air–water interface intrusion in a hydrophobic fibrous membrane comprised of orthogonally oriented fibers. This novel interface tracking algorithm is used to investigate the effects of the membrane’s microstructure and wetting properties on its resistance to water intrusion (i.e., LEP). The simulation method developed in this work is computationally affordable and it is accurate in its predictions of the air–water interface shape and position inside the membrane as a function of pressure. Application of the simulation method in studying effects of fiber diameter or contact angle heterogeneity on water intrusion pressure is reported for demonstration purposes. Capillary forces between fibrous surfaces are also studied experimentally and numerically via the liquid bridge between two parallel plates coated with electrospun fibers. In the experiment, a droplet was placed on one of the polystyrene- or polyurethane-coated plates and then compressed, stretched, or sheared using the other plate and the force was measured using a sensitive scale. In the simulation, the liquid bridge was mathematically defined for the Surface Evolver finite element code to predict its 3-D shape and resistance to normal and shearing forces, respectively, in presence of the contact angle hysteresis effect. Despite the inherent non-uniformity of the fibrous surfaces used in the experiments and the simplifying assumptions considered for the simulations, reasonable agreement was observed between the experiments and simulations. Results reveal that both normal and shear force on the plates increase by increasing the liquid volume, or decreasing the spacing between the plates.

The corrugated board is considered as the second most used packaging material and the world’s environmentally acceptable solution for packaging, with wide range of applications. After the manufacturing process, the corrugated board is cut into sheets and stored in a stack until optimum moisture content has been reached in order to avoid undesired properties. However, due to complex and various structures, it is difficult to estimate the appropriate time so to achieve the acceptable moisture level of the corrugated board stack. So a homogenized model of the stack has to be created which will have the same average properties as the real stack. In order to achieve this goal the behavior of a smaller part of the stack, the unit cell, is investigated. In the second step a homogenized model is created with the average transport of mass and heat. At the end, the unit cell is scaled up. In this master thesis, only the first and the second steps were simulated. This was achieved by creating a 3-D mathematical model using finite element method and simulating its properties in COMSOL Multiphysics®. Four mathematical models were used in the description of the 3-D model: the heat transfer, the moisture transfer, the vapour concentration and the gas pressure. Moreover, by applying the gradient in one direction in each case, the behavior of the detailed unit cell was investigated. Finally different simplified geometries were created and investigated so to approach a homogenized model which described better the average properties of the detailed model. By comparing the results of the models, it was concluded that the homogenized models 2 and 3 approached the values of the second detailed model but only inside of the unit cell. However, the deviation was not negligible and further investigation is required in order to find a new homogenized method.

京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第13021号 / 論農博第2831号 / 新制||農||1042(附属図書館) / 学位論文||H28||N4967(農学部図書室) / 32949 / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 藤原 正幸, 教授 村上 章, 准教授 宇波 耕一 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

The aviation industry aims to reduce its environmental impact through innovation and research. The usage of composite materials for multiple primary structures represents one such measure. Several alternative fuels were approved and used along with the Federal Aviation Administration (FAA). These alternative fuels are produced from wastes and biomasses. Some alternative fuels were initially only approved as drop-in fuels, meaning they must be blended with conventional fuels to operate. Fuel tanks are usually embedded into the wing structure, which is mainly made of composite materials. These composites tend to absorb fluids it encounters through their matrix phase. The absorption behavior of conventional fuels by composite materials is well documented, while alternative fuels, blended or pure, are not as widely reported. The effects of four alternative fuel blends on aerospace-grade composites were investigated and compared with the conventional fuel Jet A. No significant differences were found in weight gain. The thermomechanical properties changes were also studied, with no difference between the alternative fuel blends and the conventional fuel. Additionally, model fluids with similar chemical structures as alternative fuels were used. The uptake of these model fluids was studied cyclically and compared with Jet A and one aromatic fluid. Small differences were seen in the weight gain results, primarily due to the type of model fluids used. Also, the thermomechanical properties showed no differences between these model fluids, Jet A and the pure aromatic fluid. This means that the slight differences in weight gain did not affect the changes in properties. From the results obtained, the alternative fuels blended, and the model fluids showed no differences in effects on the thermomechanical properties versus Jet A. This implies that similar effects are expected from either type of fluids used. Finite element analysis was used to model fluid’s diffusion in composite materials using different material parameters. The parameters were fiber packing, arrangement and permeability. Each parameters impacted the equilibrium uptake and the diffusion rate differently.

The condition of fluid flow has been proven to have a significant influence on a wide variety of material processes. In electromagnetic levitation (EML) experiments, the internal flow is driven primarily by electromagnetic forces. In 1-g, the positioning forces are very strong and the internal flows are turbulent. To reduce the flows driven by the levitation field, experiments may be performed in reduced gravity and parabolic flights experiments have been adopted as the support in advance. Tracer particles on the surface of levitated droplets in EML experiment performed by SUPOS have been used to investigate the transition from laminar to turbulent flow. A sample of NiAl3 was electromagnetically levitated in parabolic flight and the laminar-turbulent transition observed from the case was studied in this work. For the sample with clearly visible tracer patterns, the fluid flow has been numerical evaluated with magnetohydrodynamic models and the laminar-turbulent transition happened during the acceleration of the flow, instead of steady state. The Reynolds number at transition was estimated approximately as 860 by the experiment record. The predicted time to transition obtained from the results of simulation showed significant difference (~ up to 300 times) compared with the time obtained from the experiment—0.37s. The discrepancy between numerical and experimental results could not be explained by the proposed hypotheses: geometry, boundary conditions or solid core. The simulations predict that the flow would become turbulent almost instantaneously after the droplet was fully molten. There are important physics shown by the simulation which were not captured.

Solutions of self-assembled wormlike micelles are used with ever increasing frequency in a multitude of consumer products ranging from cosmetic to industrial applications. Owing to the wide range of applications, flows of interest are often complex in nature; exhibiting both extensional and shear regions that can make modeling and prediction both challenging and valuable. Adding to the complexity, the micellar dynamics are continually changing, resulting in a number of interesting phenomena, such as shear banding and extensional flow instabilities. Presented in this thesis are the results of an investigation into the flow fields generated by both a controllable and idealized porous media, effected as a periodic array of cylinders as well as a single circular cylinder. In order to fully characterize the kinematics, two rheologically documented test fluids were used. The first test channel geometry consists of six equally spaced cylinders, arranged perpendicular to the flow, while the second consists of a single circular cylinder. By systematically varying the Deborah number, the flow kinematics, stability and pressure drop were measured. A combination of particle image velocimetry in conjunction with flush mount pressure transducers were used to characterize the flow, while flow induced birefringence measurements were used to determine micelle deformation and alignment. In the periodic geometry, the pressure drop was found to decrease initially due to the shear thinning of the test fluid, and then exhibit a dramatic upturn as other elastic effects begin to dominate in one of the test fluids. In the case of the single cylinder, no such upturn was observed. Presented is evidence of the onset of an elastic instability in one of the test fluids above a critical Deborah number, manifest in fluctuating transient pressure drop measurements and asymmetric streamlines. This instability was observed in both test geometries. It is argued that this instability can be attributed to the measurable differences in the extensional rheology of the two fluids.