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Annual bluegrass (Poa annua L.) is a problematic weed in turfgrass that has evolved resistance to twelve different herbicide sites of action. The mitotic-inhibiting herbicide pronamide has both pre- and post-emergence activity on susceptible annual bluegrass populations. Still, post-emergence activity may be compromised in some resistant populations due to the lack of root uptake or an unknown foliar resistance mechanism. Spray droplet size may affect foliar and soil deposition of pronamide, thus potentially explaining variation in population control or differential foliar and root uptake. Pronamide, flazasulfuron, and pronamide + flazasulfuron deposition were quantified on annual bluegrass as affected by spray-droplet size. The efficacy of these herbicide treatments in resistant (R) and susceptible (S) annual bluegrass populations was then evaluated with two droplet sizes (400 and 1000 μm). Absorption and translocation of pronamide were investigated in R and S populations following foliar-only and soil-only pronamide applications.

Black liquor, a byproduct from pulp production, is burned in a recovery boiler to generate electricity and recover inorganic materials. Black-liquor-droplet combustion is fundamental to understanding and potentially improving recovery boiler performance. This investigation reports comprehensive experimental data collected for a suite of five liquors. All the data were collected with newly-designed laboratory equipment, several aspects of which are unique. Single droplets were suspended on a thermocouple and heated in a furnace. Simultaneous diameter (size and shape), internal and surface temperatures, surface emissivity, and mass were measured under various furnace temperatures and gas compositions. The images recorded by the cameras show the droplet swelling characteristics during combustion. Droplets swell more in inert environments and with low heating-rates than in oxidizing environments and with high heating-rates. Softwood liquors show greater swelling than softwood/hardwood mixed liquors. The internal temperature measured by the thermocouple is lower than the surface temperature measured with the optical pyrometer. This temperature gradient between the droplet interior and surface can be larger than 300 K. Molecular-beam mass spectrometry data were used to determine droplet mass loss and off-gas composition. These mass-loss data differ by about 10% from the balance mass data. These data provide a self-consistent and reasonably comprehensive description of black-liquor-droplet reactivity. A one-dimensional transient droplet model predicts droplet temperatures and mass loss comparable to the data. The combustion of volatiles, droplet swelling, and enthalpy of devolatilization were proved to be significant. Intermediate-sized particle (ISP) formation was investigated with a suspended-droplet experimental technique. The images indicate that a small amount of particles are ejected during drying. Insignificant ISP formation during devolatilization occurs. Char burning and smelt oxidation produce the largest amount of ISP. Quantitative analyses indicate that both droplet solids-content and liquor type impact ISP formation. Longer burning times produce more ISP, with total ISP formation being 0.2-2% of dry solids. Sampled ISPs show consistent trends in surface structure and particle sizes under a scanning-electron-microscope, independent of the experimental conditions.

Black liquor is an intermediate product of pulp production. Recovery boilers process black liquor to recover the inorganic material for recycling in the mill and to generate electricity and steam for the paper mill. Black liquor droplet combustion rates and mechanisms dictate many aspects of recovery boiler performance. This investigation documents new experimental data on single droplet pyrolysis and combustion in a laboratory furnace that mimics many of the essential features of commercial boilers (temperature, composition, droplet size, etc.). These experiments monitored single droplets placed on a thermocouple wire and suspended from a mass balance. Simultaneous video images and pyrometry data provide mass loss and internal temperature data. These investigations provide an extensive data set from which to validate a model and insight into the mechanisms of combustion. Particles burning in air expelled ejecta from the particle during the entire combustion process, though ejection rates during the late stages of char combustion were observed to be higher than during other stages. In addition, char burning began almost the instant the particle entered the reactor; showing significant overlap in the combustion processes. A transient, 1-dimensional, single-droplet model describes droplet combustion. This model solves the momentum, energy, species continuity, and overall continuity equations using the control volume method. The model uses the power-law scheme for combined advection diffusion, and the fully-implicit scheme for the time step. It predicts internal velocities, gas and solid temperatures (assumed equal), pressure, and composition. Pressure and velocity equations use Darcy's Law for flow through a porous medium. Modeling results show the large effect of swelling on all particle properties. This model describes the flame region by extending the control volume into the gas phase.

Evaporation of pure and binary liquid droplets is of interest in thermal sprays and spray drying of food, ceramics and pharmaceutical products. Understanding the rate of heat and mass transfer in any drying process is important not only to enhance evaporation rate or vapor-gas mixing, but also to predict and control the final morphology and microstructure of the precipitates. Acoustic levitation is an alternative method to study micron-sized droplets without wall effects, which eliminates chemical and thermal contamination with surfaces. This work uses an ultrasonic levitation technique to investigate the vaporization dynamics under radiative heating, with focus on evaporation characteristics, precipitation kinetics, particle agglomeration, structure formation and droplet stability. Timescale and temperature scales are developed to compare convective heating in actual sprays and radiative heating in the current experiments. These relationships show that simple experiments can be conducted in a levitator to extrapolate information in realistic convective environments in spray drying. The effect of acoustic streaming, droplet size and liquid properties on internal flow is important to understand as the heat and mass transfer and particle motion within the droplet is significantly controlled by internal motion. Therefore, the droplet internal flow is characterized by Particle Image Velocimetry for different dropsize and viscosity. Nanosuspension droplets suspended under levitation show preferential accumulation and agglomeration kinetics. Under certain conditions, they form bowl shaped structures upon complete evaporation. At higher concentrations, this initial bowl shaped structure morphs into a ring structure. Nanoparticle iv migration due to internal recirculation forms a density stratification, the location of which depends on initial particle concentration. The time scale of density stratification is similar to that of perikinetic-driven agglomeration of particle flocculation. The density stratification ultimately leads to force imbalance leading to a unique bowl-shaped structure. Chemically active precursor droplet under acoustic levitation shows events such as vaporization, precipitation and chemical reaction leading to nanoceria formation with a porous morphology. The cerium nitrate droplet undergoes phase and shape changes throughout the vaporization process followed by formation of precipitate. Ex-situ analyses using TEM and SEM reveal highly porous morphology with trapped gas pockets and nanoceria crystalline structures at 70oC. Inhomogeneity in acoustic pressure around the heated droplet can induce thermal instability. Short wavelength (Kelvin-Helmholtz) instability for diesel and bio-diesel droplets triggers this secondary atomization, which occurs due to relative velocity between liquid and gas phase at the droplet equator. On the other hand, liquids such as Kerosene and FC43 show uncontrollable stretching followed by a catastrophic break-up due to reduction in surface tension and viscosity coupled with inhomogeneity of pressure around the droplet. Finally, a scaling analysis has been established between vaporizing droplets in a convective and radiative environment. The transient temperature normalized by the respective scales exhibits a unified profile for both modes of heating. The analysis allows for the prediction of required laser flux in the levitator experiments to show its equivalence in a corresponding heated gas stream. The theoretical equivalence shows good agreement with experiments for a range of droplet sizes.

Icing on aircraft wings is one of the leading causes of aircraft crashes. It is mainly caused due to accumulation of ice or snow on the wing surface due to impact with supercooled droplets when passing through clouds at high altitudes, causing loss of lift obtained by the wings. It was found that droplet impact characteristics are dependent on droplet size, surface roughness, surface material hydrophobicity, and droplet impact velocity. As a continuation of the study of droplet impact contact characteristics by varying surface roughness and impact velocity, this study focuses on droplets impacting the vibrating surface at frequencies between 2-7 kHz. Atomization (water drop splitting into smaller droplets and ejecting from the surface) has been observed at different rates for all frequencies. The first set of data is collected by keeping roughness constant and increasing the amplitude of the vibration to observe the critical amplitude at which atomization is initiated. The surface roughness is varied for the second set of experiments. The data is quantified using image processing of the high-speed videos to obtain the rate of ejection for each case. / Master of Science / Icing on aircraft wings is among the leading causes of crashes, which involves small freezing water drops sticking to the wing surface thus reducing the lift. This study is an investigation to experimentally observe how small water droplets interact with surfaces vibrating at high frequencies when impacted. Surface roughness, materials, droplet velocities, and frequency of vibration have been varied and the droplet was captured using high-speed photography to study their effect on the aforementioned interaction. Glass, PET-G. and aluminum having specific roughness were fabricated using laser and chemical etching. Atomization (water drop splitting into smaller droplets and ejecting from the surface) has been observed at different rates for all frequencies. A relation between the amplitude of the vibration and the rate of atomization was found. The effect of varying frequencies and surface roughness has also been documented.

No / A computational fluid dynamics (CFD) model is used to investigate the droplet formation and deformation under the influence of different parameters. Droplet breakup phenomenon depends on several factors such as viscosity, velocity, pressure difference, and geometry. The most important parameter for droplet breakup is the Weber number (We) which is the ratio of disrupting aerodynamics forces to the surface tension forces. Volume of fluid (VOF) model is used in present work to simulate the droplet breakup. This work presents the effect of liquid velocity, viscosity, and orifice diameters on droplet formation and breakup.

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

<p> A brief review of the theoretical and experimental aspects of liquid droplet nucleation from vapours and of crystal nucleation from aqueous solution is presented. In order to study the nucleation and crystal growth of several analytically important metal chelates, methods were developed to measure the size distribution of crystals growing in a supersaturated solution. These methods involved rapid mixing techniques followed by measurement of the size distribution of the precipitated particles using a Coulter counter and multichannel analyser. The size distributions were dumped from the analyser onto magnetic tape and recovered using computer methods. The mixing and counting techniques were calibrated and tested using barium sulphate and spheres of known size distribution. </p> <p> From the size distributions obtained for the metal chelates, conclusions were made regarding the nucleation step, and the parameters important in the classical Volmer-Weber-Becker-Doring theory of nucleation were calculated. The validity of the values were evaluated and comparisons made with values obtained by other workers. </p> <p> The laws controlling the crystal growth of the metal chelates and their importance in elucidating the type of nucleation process were also investigated. </p> / Thesis / Doctor of Philosophy (PhD)

This is a `sandwich thesis' comprising three distinct research streams I have pursued during the course of my master's degree. The first two streams have concluded, each resulting in a manuscript that is presented as a separate chapter of this thesis. The third research stream is ongoing, but preliminary results are presented in another chapter of this thesis. The first research stream presented in this thesis concerns the development of a technique to produce droplets with diameters as small as 5 microns with an extremely narrow size distribution in comparison to other methods. Other advantages of this technique, known as he snap-offf method, include its simplicity and ease of tuning droplet size. The results of this research are presented in chapter 3 in the form of a manuscript that is currently in press. The second research stream of this thesis explores the physics that drive droplet snap-off. A model was developed to predict the size of droplets, dependent on fluid properties, system geometry, and fluid flow rate. Experiments examined each of these parameters in turn, providing a cohesive understanding of the mechanism behind droplet snap-off. Multiple unanticipated predictions of the model were also verified experimentally. This research is presented in chapter 4 as a manuscript that will be submitted shortly. The final research stream of this thesis investigates forces in emulsions as they relate to a transition from glassy to crystalline dynamics. Specifically, 2D aggregates of droplets were compressed with micropipettes, providing both imaging of cluster evolution, as well as the force applied during compression. This research stream has demonstrated qualitative differences between droplet clusters that differ in composition so as to behave like crystals, glasses, or intermediate states. More quantitative analysis is required before this research stream is ready to be published. Preliminary results are presented in chapter 5. / Thesis / Master of Science (MSc)