<p>Mass transfer in a porous solid, partially saturated with asingle solvent and multicomponent liquid mixtures, has beenexperimentally and theoretically studied. A porous materialcontaining single liquids and mixtures of organic solvents wasisothermally dried. Experiments were performed using a jacketedwind tunnel, through which a humidity andtemperature-controlled air stream flowed. The wetted porousmaterial was placed in a cylindrical vessel, whose top isexposed to the air stream until the material became dried to acertain extent. Drying experiments with the single solventswater, methanol, ethanol and 2-propanol, were performed atdifferent temperatures and transient liquid content profileswere determined. In isothermal drying experiments with liquidmixtures,the transient concentration profiles of thecomponents along the cylindrical sample as well as the totalliquid content were determined. The liquid mixtures examinedwere water-methanolethanol and isopropanol-methanol-ethanol.Two different temperatures and initial compositions were usedin the experiments. Mathematical models that describe nonsteadystate isothermal drying of a solid containing single liquidsand multicomponent liquid mixtures were developed. In the solidwetted with a single liquid, capillary movement of the liquidwas the main mechanism responsible for mass transfer. In thesolid containing liquid mixtures, interactive diffusion inliquid phase was superimposed to the capillary movement of theliquid mixture. In addition, interactive diffusion of thevapours in empty pores was considered. The parameters todescribe the retention properties of the solid and thecapillary movement of the liquid were determined by comparingtheoretical and experimental liquid content profiles obtainedduring drying of the solid wetted with single liquids. Tosimulate the transport of the liquid mixtures these parameterswhere weighed according to liquid composition. A fairly goodagreement between theoretical and experimental liquidcomposition profiles was obtained if axial dispersion isincluded in the model when the moisture consists of amixture.</p><p><b>Keywords:</b>Internal mass transfer, capillary flow,multicomponent, diffusion, solvent mixtures</p>

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 87-123).

Drop impacts play a key role in many industrial applications, from spray coating of surfaces, to splashing of fuel-droplets within combustion chambers. Splashing, or break-up during ink-jet printing, can cross-contaminate biological assays, or degrade the quality of ink-jet printed products. Crime scene studies of blood splatter can give vital clues for the police. Spreading of plant diseases between nearby leaves by splashing depends on the velocity and trajectory of secondary droplets. In this dissertation, I study the early dynamics of splashing and the dynamics of ejecta sheets under extreme impact conditions, using ultra-high-speed video imaging at up to 5 million fps. In the first part, I show the effect of the surface tension differences on the break-up of the Edgerton crown, I verify that individual droplets hit the crown wall and generated Marangoni holes, thereby causing the crown wall to rupture at multiple locations. In the second part, I investigate the splashing of a drop impacting onto a solid substrate with high impact velocity, I show that for sufficiently high Re, splashing can no longer be suppressed by only reducing the surrounding air pressure. Furthermore, I tracked the earliest splashed spray droplets to catch their maximum velocity. Surprisingly, the splashed droplets can travel at extremely high speed of up to 1 km/s, which is 50 times faster than the impact speed. The influence of viscosity on the lamellar spreading along the substrate was investigated. I find that the intact lamella, following the fine spray, spreads as R(t) ~〖 t〗^(1/3) , while the maximum spreading radius of the drop was shown to be a strong function of viscosity, scaling as β_max∝〖Re〗^0.175. The data did not show a strong effect of surface tension on β_max over a wide range. Therefore, I concluded that surface tension at this parameter space does not play a major role in both splashing nor spreading. In the third part, I study extreme splashing dynamics of the Ejecta sheet when a drop impacts on a thin liquid film with very large impact velocities using the same device, at up to ~ 22 m/s. For this purpose, we have constructed a novel experimental device consisting of a 26-m-tall vacuum tube. I investigate the interplay between viscosity, the surrounding ambient air pressure, and surface tension, on the ejecta shapes and break-up. I show how the bending of the ejecta sheet is primarily produced by air-resistance. This is supported by an analytical and numerical model to quantify the effect of the surrounding air pressure on the sheet bending and touch-down.

Mass transfer in a porous solid, partially saturated with asingle solvent and multicomponent liquid mixtures, has beenexperimentally and theoretically studied. A porous materialcontaining single liquids and mixtures of organic solvents wasisothermally dried. Experiments were performed using a jacketedwind tunnel, through which a humidity andtemperature-controlled air stream flowed. The wetted porousmaterial was placed in a cylindrical vessel, whose top isexposed to the air stream until the material became dried to acertain extent. Drying experiments with the single solventswater, methanol, ethanol and 2-propanol, were performed atdifferent temperatures and transient liquid content profileswere determined. In isothermal drying experiments with liquidmixtures,the transient concentration profiles of thecomponents along the cylindrical sample as well as the totalliquid content were determined. The liquid mixtures examinedwere water-methanolethanol and isopropanol-methanol-ethanol.Two different temperatures and initial compositions were usedin the experiments. Mathematical models that describe nonsteadystate isothermal drying of a solid containing single liquidsand multicomponent liquid mixtures were developed. In the solidwetted with a single liquid, capillary movement of the liquidwas the main mechanism responsible for mass transfer. In thesolid containing liquid mixtures, interactive diffusion inliquid phase was superimposed to the capillary movement of theliquid mixture. In addition, interactive diffusion of thevapours in empty pores was considered. The parameters todescribe the retention properties of the solid and thecapillary movement of the liquid were determined by comparingtheoretical and experimental liquid content profiles obtainedduring drying of the solid wetted with single liquids. Tosimulate the transport of the liquid mixtures these parameterswhere weighed according to liquid composition. A fairly goodagreement between theoretical and experimental liquidcomposition profiles was obtained if axial dispersion isincluded in the model when the moisture consists of amixture. Keywords:Internal mass transfer, capillary flow,multicomponent, diffusion, solvent mixtures

<div>The evaporation of a liquid drop containing particles resting on a substrate have diverse industrial applications including inkjet printing, spray coating, fabrication of functional nanomaterials, disease diagnosis, among others. In addition to these wide ranging practical applications, the sessile drop evaporation can be observed in everyday life with dew drops, coffee spills, and the dry patterns of other beverages.</div><div><br></div><div>The self-assembly of particles during drop evaporation is a process that is affected by various factors, such as contact line (CL) behaviors, microfluidic flows, short-range interactions of particle-interface and particle-particle. Each of these factors are complicated enough to study, let alone the total effects on the process. The primary goal of this work is to investigate the influence of microfluidic flows and the particle-interface interaction, viz. the evaporation process was subject to a pinned CL and the particle-particle interaction was neglected under dilute particle concentration. </div><div>To accomplish this goal, the Galerkin/Finite Element Method (G/FEM) is used to solve for the flow, the temperature and the particle concentration profiles. </div><div><br></div><div><br></div><div>The complexity of the problems comes from various surface phenomena, one of which is the surface tension. The surface tension brings capillary force in the normal direction and capillary flow toward the CL, which results in the well-known coffee-ring effect. Moreover, the surface tension changes with temperature, surfactant concentration, etc. resulting in Marangoni stresses in the tangential direction. The Marangoni stress on the surface leads to circulations of flow inside the drop and the circulation can be either clockwise or counterclockwise depending on the direction of the stress. </div><div><br></div><div>When the Marangoni stress is merely caused by temperature change, the circulation direction changes not only in time but also in space. At late stage of evaporation, i.e. with a small contact angle (CA), multi-circulation flow profiles emerge. This flow profiles are featured with stagnation points and transition points. The stagnation points can be further categorized into capillary-induced stagnation points and Marangoni-induced stagnation points. By introducing the concept of capillary-induced stagnation points, the simulations reached agreement with experiments in terms of the radial location of the observed stagnation points.</div><div><br></div><div><br></div><div>The multi-circulation flow profiles implied regional segregation inside the drop. When a large circulation is observed in most part of the drop and a small circulation exists near the CL, particle concentrations are relatively uniform in each individual region but differs significantly across the two regions. Transition points are used to characterize the location of the regional segregation, which can be adjusted by Marangoni stress.</div><div><br></div><div><br></div><div>Marangoni circulations in different directions revealed distinct influences on particle distribution and deposition. First, while both directions facilitate even distribution of particles, a clockwise circulation strengthens CL accumulation for a small Marangoni stress. Second, a counterclockwise circulation with a small Marangoni stress impedes the deposition rate of particles, while a clockwise circulation facilities the deposition no matter how small the Marangoni stress is. This results is under a condition of a strong adsorption between particles and substrates. </div><div><br></div><div>The analysis and understanding of the above results are crucial to elucidating and controlling the final deposition patterns of particles. Thus, the focus of this research is to understand the combined effect of Marangoni stress and capillary flow on particle deposition during sessile drop evaporation.</div><div><br></div>

This work involves investigation of the kinetics data of a joint formation during aluminum alloy brazing. Data was generated by several groups of experiments conducted under conditions of a controlled oxygen level of the background brazing atmosphere. Generated data are examined to identify the phases of the joint formation and the time frame of its evolution. Specifically, the triple line kinetics data are analyzed to verify whether a power law between (1) the triple line of the molten metal preceding joint formation and (2) the formation time can be established for each formation phase. In addition, both initial and residual clad thicknesses on brazing sheets are studied to check phenomenologically an impact of silicon diffusion on joint formation. Formation shapes are also inspected in order to study if a 2-D configuration of joint formation is present. The kinetics data from different sets of experiments under adverse atmosphere conditions are compared to understand the impact of oxygen level on joint formation. This study is not necessarily aimed at building a mathematical model for T-Joint formation during brazing process, but intends to understand possible influential parameters on the development of the formation. KEYWORDS: Aluminum Brazing, Kinetics, T-Joint, Background Atmosphere, Capillary Flow.

Le processus d'étalement et d'évaporation d'une goutte de suspensions de particules sur une surface solide est très intéressant permettant la formation de motifs. Une étude expérimentale à été effectuée avec du sang total humain et avec des fluides purs dans une chambre sous atmosphère contrôlée en humidité relative. Pour des angles de contact faible, le processus d'étalement/évaporation peut être divisé en deux régimes. Un premier régime rapide gouverné par un équilibre entre les forces visqueuses et les forces capillaires et un deuxième régime plus lent dominé par la cinétique d'évaporation. Nous montrons que les bio-colloïdes jouent un rôle significatif sur la dynamique de la ligne de contact. La vitesse moyenne de la ligne de contact suit la même dynamique d'étalement que le modèle de Tanner, où le temps d'étalement et les paramètres géométriques de la goutte sont fonctions de l'humidité. Dans cette étude, nous montrons que l'humidité relative influence les paramètres géométriques de la goutte et par conséquent le motif a la fin du processus d'évaporation. Un modèle purement diffusif pur a été obtenu dont le diamètre de mouillage et l'angle de contact sont fonction de l'humidité. Pour l'analyse morphologique des motifs de craquelures, une méthode de segmentation manuelle a été utilisée comme une méthode de référence pour la validation de la méthode de segmentation automatique développée dans "iBlood". Par cette méthode, nous montrons que la cinétique d'évaporation influence la distribution structurelle et morphologique des cellules de forme trapézoïdale, et par conséquent, l'espacement des fractures moyenne finale. / Spreading/evaporation process of droplets over solid surfaces is a fundamental process and a wide research field because of number of applications in printing, micro-electronics, DNA analysis and even in biomedical. This experimental work aims to investigate the effect of relative humidity on the contact line dynamics, on the evaporation dynamics and on the final pattern of a drop of whole human blood. The spreading of a pure fluid model that has the same physical properties as human blood was studied and compared to the blood. We showed that bio-colloids play significant effect on the dynamics of contact line and the pinning effect of the drop. For low contact angles, we showed that the spreading/evaporation process could be divided into two regimes. A fast first regime determined by a balance between viscous forces and capillary forces and a second slower regime dominated by the evaporation rate. Physical mechanisms that are responsible for the spreading enhancement are proposed and discussed. The average velocity of the contact line was found to follow the same behaviour as Tanner's model, where the spreading dynamics and geometrical parameters of the droplet are function of relative humidity. The experimental measurements are in a good agreement with the purely diffusive model where the equilibrium wetting radius and contact angle are function of relative humidity. For the morphological analysis of crack patterns, a manual segmentation method was used as a reference for the validation of the automatic developed segmentation method. We showed that the evaporation rate influences structural distribution of plaques in the corona region and hence, the mean crack spacing.

No description available.

Homogenous and separated flow methods have been presented for use in the capillary tube section of the Plasma Rapid Expansion of Supercritical Solutions (PRESS) process using a carbon dioxide and ethanol mixture as the working fluid. Each method was validated against experimental expansion processes using pure carbon dioxide, isobutane, and R-134a. The results have indicated that both the homogenous flow method and the separated flow method produce results within an acceptable margin of error. By accounting for the phase interactions the separated flow method produces more accurate results with mean errors of 8.03%, 4.57%, and 5.77% for carbon dioxide, isobutane, and R-134a, respectively. In comparison, the mean errors of the homogenous method were 8.17%, 5.4%, and 8.55%, respectively. The homogenous and separated flow methods were shown to be statistically and significantly different for 95% confidence, which demonstrates that the accuracy of capillary flow simulation can be increased through the use of the separated flow method. A method to extend the methods for the mixture of carbon dioxide and ethanol was implemented in a limited fashion. Under certain conditions the carbon dioxide and ethanol mixture results in the trivial root problem associated with the cubic compressibility equation. As literature on the subject of the trivial root problem is limited, the expansion process was focused on a region where three real roots exist to the compressibility equation. A simulation of a carbon dioxide and ethanol mixture expansion process was successfully implemented at a low temperature using the homogenous flow method. For validation, a VLE diagram was created for the mixture and compared adequately with experimental results.

<div>Red blood cells (RBCs) make up 40-45% of blood and play an important role in oxygen transport. That transport depends on the RBC distribution throughout the body, which is highly heterogeneous. That distribution, in turn, depends on how RBCs are distributed or partitioned at diverging vessel bifurcations where one vessel flows into two. Several studies have used mathematical modeling to consider RBC partitioning at such bifurcations in order to produce useful insights. However, these studies assume that the vessel wall is a flat impenetrable homogeneous surface. While this is a good first approximation, especially for larger vessels, the vessel wall is typically coated by a flexible, porous endothelial surface layer (ESL) that is 0.5-1 microns thick. To better understand the possible effects of this layer on RBC partitioning, a diverging capillary bifurcation is analyzed using a flexible, two-dimensional RBC model. The model is also used to investigate RBC deformation and penetration of the ESL region when ESL properties are varied. The RBC is represented using interconnected viscoelastic elements. Stokes flow equations (viscous flow) model the surrounding fluid. The flow in the ESL is modeled using the Brinkman approximation for porous media with a corresponding hydraulic resistivity. The resistance of the ESL to compression is modeled using an osmotic pressure difference. The study includes isolated cells that pass through the bifurcation one at a time with no cell-cell interactions and two cells that pass through the bifurcation at the same time and interact with each other. A range of physiologically relevant hydraulic resistivities and osmotic pressure differences are explored.</div><div><br></div><div>For isolated cell simulations, decreasing hydraulic resistivity and/or decreasing osmotic pressure difference produced four behaviors: 1) RBC distribution nonuniformity increased; 2) RBC deformation decreased; 3) RBCs slowed down slightly; and 4) RBCs penetrated more deeply into the ESL. The presence of an altered flow profile and the ESL's resistance to penetration were primary factors responsible for these behaviors. In certain scenarios, ESL penetration was deep enough to present a possibility of cell adhesion, as can occur in pathological situations.</div><div><br></div><div>For paired cell simulations, more significant and complex changes were observed. Three types of effects that alter partitioning as hydraulic resistivity is changed are identified. Decreasing hydraulic resistivity in the ESL produced lower RBC deformation. Including cell-cell interactions tended to increase deformation sharply compared to isolated cell scenarios. ESL penetration generally decreased for lower hydraulic resistivities except in scenarios with significant cell-cell interactions. This was primarily due to changes in flow profiles induced by the altered hydraulic resistivity levels.</div>