Yes / The coating flow examined here, labelled angled dip coating, is that where a substrate enters a pool of liquid forming an angle ß with the vertical so that it intersects the liquid along a wetting line which is not perpendicular to the direction of its motion. This flow situation is distinctly different from that where the substrate, inclined in the other dimension by the so-called angle of entry ¿, intersects the liquid surface perpendicularly to its motion. Experiments were carried out with various liquids to determine the effect of ß on the substrate velocity at which air is entrained into the liquid. It was observed that as this angle departs from zero, air entrainment is delayed to higher speeds. The data show that the speed which is relevant to air entrainment is not the velocity of the substrate itself but its component normal to the wetting line. This result has important practical implications and suggests that this fundamental principle is also applicable to other coating flows.

Yes / Self-aeration in open channel flows occurs owing to free surface air entrainment. Self-aeration development and fully cross-sectional distribution of air concentration are not thoroughly understood. In the present study, an analytical solution for the averaged cross-sectional air concentration in the gradually varying region is established using a simplified mechanism of free surface air entrainment. For a fully cross-sectional distribution of air concentration affected by the channel bottom, a model of a diffusion region without wall restraint is proposed, and two situations are classified based on averaged cross-sectional air concentration. Good agreement between measured data and calculations is obtained, and the computational accuracy of the air concentration distribution near the wall is improved. The results reveal that the channel slope determines the air entrainment quantity, while water flow discharge determines the self-aeration evolution distance. The solutions for the averaged cross-sectional air concentration and the effect of the bottom wall on air diffusion promote air–water flow applications in hydraulic engineering practices. / This work was supported by National Natural Science Foundation of China [grant numbers 51939007, 51979183]; Sichuan Province Science and Technology support program [grant number 2019JDTD0007].

The objective of the present study was to acquire a better understanding of parameters controlling the species generation and transport from compartment fires. The experiments were performed in a half-scale ISO 9705 compartment and a 6.1 m long hallway connected in a head-on configuration. The buoyancy driven propane fire was provided by a burner and a continuous gaseous fuel supply system. All the measurements were obtained during the steady state of the fire. The ventilation conditions were fixed and three different fire source elevations were studied for heat release rates ranging from 20 kW to 150kW. The species yields were obtained from performing detailed mapping measurements at the compartment and hallway exit planes. The measurements included local specie mole fractions of oxygen, carbon dioxide, carbon monoxide and unburned hydrocarbons. The local temperature and the local pressure (for local gas velocity calculations) were also measured. In addition, visual observations of the flow dynamic were performed through a window and the vents to give useful insights and lead to a better understanding of the combustion process. The data obtained from the species generation study was analyzed using previously developed methods. The method based on equivalence ratio was presented and determined inappropriate for the present study where the global equivalence ratio was not equal to the plume equivalence ratio due to the complexity of the fire dynamic taking place. The method consisting of correlating the species yields based on the combustion within the compartment as a function of a non dimensional heat release rate allowed qualitative conclusions to be made. The non-dimensional heat release rate was based on the fuel load and the geometric parameters of the compartment. This methodology revealed similarities in the species production between the three fire source elevations investigated. A correlation of the data was obtained based on experimental data. The transport of species to remote locations was studied for the three fire source elevations and fixed ventilation conditions. Species mole fractions and yields were obtained at the compartment exit plane (compartment/hallway interface) and at the hallway exit plane. The results were compared for various heat release rates and showed differences for some scenarios attributed to mixing along the hallway and oxidation reactions outside the compartment. / Master of Science

Em inúmeras aplicações práticas da engenharia a camada interfacial entre dois fluidos é de extrema importância para a correta caracterização do escoamento. Especificamente na Engenharia Ambiental e Hidráulica na interface entre o ar e a água existem propriedades capazes de relacionar a aeração e oxigenação. Focado na dinâmica dos processos turbulentos, o estudo proposto se aplica a problemas de sub-pressão em vertedores e visa analisar a troca de gases da interface ar-água em situações de fases dispersas e avaliar a qualidade da água a jusante dos mesmos. O objetivo maior é descrever a relação entre o comportamento da superfície da água, o desenvolvimento da camada limite e os regimes de escoamento de acordo com a vazão volumétrica. Para representar a distribuição da fração de vazios da fase dispersa, foram usados os princípios da formulação dos escoamentos em vertedores escalonados e da formulação para enlaçamento de ar. As argumentações e justificativas das formulações propostas para os perfis de concentrações foram baseadas na distribuição da fração de vazios prevista numericamente. A abordagem numérica do problema fluidodinâmico diferencia da maioria dos estudos concentrados na literatura, por estar baseada na quebra da superfície livre. / In many pratical aplications of engineering the interfacial layer between two fluids has a strong relevance in the process of right measurements of the flow. Espeficically in the enviromental and hydraulics engineering the interface between air and water is the property related with oxigen and areation of the flow. With focus on the dynamics of the turbulent processes, the proposed study is applied to sub-pressure problems in spillways. It investigates the gases exchange in the air- water interface in the dispersed phase and evaluate the water quality downstream. The major goal is to describe a relation between the boundary layer development and the flow regimes with discharge. To represent the distribution of void fractions of the dispersed phase, the physical formulation concepts of stepped spillways and entrapped air were used. The arguments and reasons to justify the proposed concentration profile formulation are based on the numerical provided void fraction distribution. The results as well as the physical model are in good agrement with described literature data. The Numerical approach of the fluid dynamics problem differs from major of described literature studies because it is based on the surface breakup.

Em inúmeras aplicações práticas da engenharia a camada interfacial entre dois fluidos é de extrema importância para a correta caracterização do escoamento. Especificamente na Engenharia Ambiental e Hidráulica na interface entre o ar e a água existem propriedades capazes de relacionar a aeração e oxigenação. Focado na dinâmica dos processos turbulentos, o estudo proposto se aplica a problemas de sub-pressão em vertedores e visa analisar a troca de gases da interface ar-água em situações de fases dispersas e avaliar a qualidade da água a jusante dos mesmos. O objetivo maior é descrever a relação entre o comportamento da superfície da água, o desenvolvimento da camada limite e os regimes de escoamento de acordo com a vazão volumétrica. Para representar a distribuição da fração de vazios da fase dispersa, foram usados os princípios da formulação dos escoamentos em vertedores escalonados e da formulação para enlaçamento de ar. As argumentações e justificativas das formulações propostas para os perfis de concentrações foram baseadas na distribuição da fração de vazios prevista numericamente. A abordagem numérica do problema fluidodinâmico diferencia da maioria dos estudos concentrados na literatura, por estar baseada na quebra da superfície livre. / In many pratical aplications of engineering the interfacial layer between two fluids has a strong relevance in the process of right measurements of the flow. Espeficically in the enviromental and hydraulics engineering the interface between air and water is the property related with oxigen and areation of the flow. With focus on the dynamics of the turbulent processes, the proposed study is applied to sub-pressure problems in spillways. It investigates the gases exchange in the air- water interface in the dispersed phase and evaluate the water quality downstream. The major goal is to describe a relation between the boundary layer development and the flow regimes with discharge. To represent the distribution of void fractions of the dispersed phase, the physical formulation concepts of stepped spillways and entrapped air were used. The arguments and reasons to justify the proposed concentration profile formulation are based on the numerical provided void fraction distribution. The results as well as the physical model are in good agrement with described literature data. The Numerical approach of the fluid dynamics problem differs from major of described literature studies because it is based on the surface breakup.

Defect generation and propagation in thin films, such as separation membranes, can lead to premature or catastrophic failure of devices such as polymer electrolyte membrane fuel cells (PEMFC). It is hypothesized that defects (e.g., air bubbles, pin-holes, and holes) originate during the manufacturing stage, if precise control is not maintained over the coating process, and they propagate during system operation. Experimental and numerical studies were performed to detect and eliminate defects that were induced during slot die coating of high-viscosity (1 to 40 Pa-s), shear-thinning solutions. The effects of fluid properties, geometric parameters and processing conditions on air entrainment and coating windows (limited set of processing conditions for which defect-free coating exists) were studied. When smaller slot gaps and coating gaps were used, relatively small bubbles were entrained in the coated film. The air bubble sizes increased as the viscosity of the coating solution decreased. A semi-empirical model correlating the maximum coating speed to a solution's material properties, geometric parameters and processing conditions was developed. Such a predictive model will enable engineers to determine the maximum coating boundary for shear-thinning and Newtonian solutions within certain constraints. Smaller coating gaps and low-viscosity solutions produced higher coating speeds. The surface tension property of the coating solution provided stability to the coating bead. Therefore, solutions with higher surface tension could be processed at higher coating speeds.

If air is entrained in a bottom outlet of a dam in an uncontrolled way, the resulting air pockets may cause problems such as blowback, blowout and loss of discharge capacity. In order to provide guidance for bottom outlet design and operation, this study examines how governing parameters affect air entrainment, air-pocket transport and de-aeration and the surrounding flow structure in pipe flows. Both experimental and numerical approaches are used. Air can be entrained into the bottom outlet conduit due to vortex formation at the intake if the intake submergence is not sufficient. The influent of the intake entrance profiles and channel width on the critical submergence were studied in the experiment. The experimental study was performed to investigate the incipient motion of air pockets in pipes with rectangular and circular cross sections. The critical velocity is dependent on pipe slope, pipe diameter, pipe roughness and air-pocket volume. If the pipe is horizontal, air removal is generally easier in a rectangular pipe than in a circular pipe. However, if the pipe is downward-inclined, air removal is easier in a circular pipe. When a bottom outlet gate opens, air can become entrained into the conduit in the gate shaft downstream of the gate. Using FLUENT software, the transient process of air entrainment into a prototype bottom outlet during gate opening is simulated in three dimensions. The simulations show in the flow-pattern changes in the conduit and the amount of air entrainment in the gate shaft. The initial conduit water level affects the degree of air entrainment. A de-aeration chamber is effective in reducing water surface fluctuations at blowout. High-speed particle image velocimetry (HSPIV) were applied to investigate the characteristics of the flow field around a stationary air pocket in a fully developed horizontal pipe flow. The air pocket generates a horseshoe vortex upstream and a reverse flow downstream. A shear layer forms from the separation point. Flow reattachment is observed for large air pockets. The air―water interface moves with the adjacent flow. A similarity profile is obtained for the mean streamwise velocity in the shear layer beneath the air pocket. / <p>QC 20140211</p>

Made available in DSpace on 2014-12-17T14:08:50Z (GMT). No. of bitstreams: 1 MarcoABL_DISSERT.pdf: 3031485 bytes, checksum: ee9422376e7cb63c045cc578494d0199 (MD5) Previous issue date: 2011-02-08 / Cementing operations may occur at various stages of the life cycle of an oil well since its construction until its definitive abandonment. There are some situations in which the interest zones are depleted or have low fracture pressure. In such cases, the adoption of lowdensity cement slurries is an efficient solution. To this end, there are basically three ways to reduce the density of cement slurries: using microspheres, water extending additives or foamed cement. The objective of this study is to formulate, to study and to characterize lowdensity foamed cement, using an air entrainment surfactant with vermiculite or diatomite as water extenders and stabilizers. The methodology consists on preparation and evaluation of the slurries under the American Petroleum Institute (API) and the Brazilian Association of Technical Standards (ABNT) guidelines. Based on calculated densities between 13 and 15 ppg (1.559 and 1.799 g/cm3), the slurries were prepared with fixed surfactant concentration, varying the concentrations of vermiculite and diatomite and were compared with the base slurries. The results of plastic viscosity, yield point and gel strength and the compressive strength for 24 h showed that the slurries presented suitable rheology and mechanical strength for cementing operations in oil wells, and had their densities reduced between 8.40 and 11.89 ppg (1.007 and 1.426 g/cm3). The conclusion is that is possible, under atmospheric conditions, to obtain light weighted foamed cement slurries with satisfactory rheological and mechanical properties by means of air entrainment and mineral additions with extenders and stabilizers effects. The slurries have great potential for cementing operations; applicability in deep wells, in low fracture gradient formations and in depleted zones and bring cost savings by reducing the cementing consumption / As opera??es de cimenta??o podem ocorrer em diversas etapas do ciclo de vida de um po?o, desde a sua constru??o at? seu abandono definitivo. H? situa??es em que as zonas de interesse se apresentam depletadas ou com baixa press?o de fratura. Nesses casos, a ado??o de pastas cimentantes de baixa densidade constitui solu??o eficiente. Para tanto, h? basicamente tr?s maneiras de reduzir a densidade de pastas de cimento: usando microesferas, aditivos estendedores de ?gua ou pastas espumadas. O objetivo deste trabalho ? formular, estudar e caracterizar pastas cimentantes espumadas de baixa densidade, utilizando um surfactante incorporador de ar juntamente com adi??es de vermiculita ou diatomita como estendedores e estabilizantes. A metodologia do trabalho consiste na prepara??o e avalia??o das pastas por meio de procedimentos adotados pelo American Petroleum Institute (API) e pela Associa??o Brasileira de Normas T?cnicas (ABNT). Partindo de densidades calculadas entre 13 e 15 lb/gal (1,559 e 1,799 g/cm3), as pastas foram preparadas com dosagem fixa do surfactante, variando as concentra??es de vermiculita e diatomita e foram comparadas com pastas base. Os resultados dos ensaios que determinam viscosidade pl?stica, limite de escoamento e for?as g?is, bem como os de resist?ncia ? compress?o para tempos de 24 h mostraram que as pastas apresentaram reologia e resist?ncia mec?nica adequadas para opera??es de cimenta??o em po?os de petr?leo, al?m de terem suas densidades reduzidas entre 8,40 e 11,89 lb/gal (1,007 e 1,426 g/cm3). Conclui-se que ? poss?vel, sob condi??es atmosf?ricas, obter pastas cimentantes espumadas de baixa densidade com propriedades reol?gicas e mec?nicas satisfat?rias, por meio de incorpora??o de ar e adi??es minerais com efeitos estendedores e estabilizantes. As pastas possuem grande potencial para opera??es de cimenta??o, t?m aplicabilidade em po?os profundos, forma??es de baixo gradiente de fratura e zonas depletadas e trazem redu??es de custo pela diminui??o do consumo de cimento

Abstract A pulp suspension consists of water, fibres, fines, fillers and chemicals, but air or other gases are also present in practically all pulping processes either in dissolved form or as bubbles. Dissolved gases seldom disturb the processes, but they are readily converted to gaseous form when conditions change. The gas bubbles affect the properties of the pulp suspension, reduce the accuracy of certain measurements, interfere with the runability of the papermachine and detract from the quality of the end-product. Gases are removed from the process by either mechanical or chemical means, resulting in increased investments and operational costs. The aim of this work was to study the behaviour of gas in pulp and papermaking processes with laboratory, pilot-scale and mill-scale experiments. Five main areas of the research can be identified: 1. Occurrence of gases in pulp and paper mill processes, 2. Dissolution, precipitation and hold-up of gases in the pulp suspension and mill water, 3. Effects of gases on certain consistency measurements, centrifugal pumping and operation of the hydrocyclone. 4. Measurement of the gas content of the pulp suspension by compression, radiometric, microwave and sonar methods and 5. Removal of gases with a centrifugal pump equipped with vacuum pump or hydrocyclone equipped light reject removal. The results show that the dissolution and precipitation of gas is strongly dependent on the pulp and water properties. Dissolved and colloidal material reduces the solubility potential of gas, but also accelerates the precipitation of dissolved gases in gaseous form. The hold-up of precipitated gas bubbles was found to be much more pronounced in hydrophobic mechanical pulps than in lignin-free chemical pulps. The accuracy of consistency measurements was affected by free gas in the pulp suspension, requiring special attention when assessing the results. The operation of pressure screens and hydrocyclones was affected only at high volumes of free gas in the feed suspension. According to the experiments, a reliable gas content measurement can be achieved by in-line radiometric, microwave or sonar methods, and also by the off-line compression method if a representative sample is obtained. A centrifugal pump equipped with a gas removing unit is designed mainly to ensure undisturbed pumping, whereas its gas removal efficiency remains quite low, especially with small bubbles and at a low gas content. The gas removal efficiency of a hydrocyclone equipped with light reject removal is good, but decreases with small precipitated bubbles. These results offer new information of the behaviour of the gas in pulp suspensions and white water and underline the importance of the bubble generation mechanism in this context.

Abstract Gas removal from the papermaking process is currently a standard practice, whereas purification of the internal water circulation has become common only recently. Both unit processes have progressed greatly during recent decades and new concepts are constantly being developed. The aim of this thesis was to analyse the efficiency and applicability of a channel flow design introduced by Metso for passive white water deaeration and to study the dynamics of passive bubbly gas removal. In addition, separation of the detrimental process water components by selective flotation during deaeration was studied to add further functionality to the channel flow design. Turbulent mixing at the flow discharge and the consequent air entrainment were seen to limit the gas separation efficiency. Also, the properties of different white waters notably affect their deaeration through viscous forces, the concentration of surface active components and bubble-particle interactions. Thus similar levels of gas separation cannot be achieved with all process waters. The analysis showed that the drag of small microbubbles is mostly caused by hydrophobic contamination and the dispersed particles that readily attach to the bubbles. Correlations were derived based on experimental data to provide new information on the drag force experienced by small bubbles in white waters. Chemically unaided flotation of white water in the channel flow was shown to be efficient in separating hydrophobic contaminants that have adverse effects on paper machine production and product quality. Both good reductions in contaminant content and high selectivity in their removal were achieved. Channel flow with an overflow can be considered well suited for the first stage of froth separation, while further treatment of the channel flow reject may consist of a secondary flotation or other process that enables the recirculation of fines and fillers. Although a certain level of losses of fines and fillers must be expected, substantial fraction of these solid components can be returned to the process stream. The proposed multifunctional process, channel flow deaeration and frothing of white water, was seen to be straightforward, economical and feasible while also providing benefits in terms of total process efficiency that are not delivered by any current process scheme. The experimental parameters presented here regarding bubble dynamics and flotation efficiency can be used to achieve better models of these processes.