Interpersonal transport of expiratory droplets and droplet nuclei constitutes a prerequisite for the transmission of pathogens as well as the transmission of respiratory diseases. This study modeled the physical process of interpersonal transport of droplets and droplet nuclei in a ventilated room. The impacts of a number of parameters in three length scales and three corresponding physical processes were analyzed, including dispersion and evaporation of droplets/droplet nuclei at 1 to 100 μm, human exhalation flows and body plumes at 0.1 to 1 m, and the indoor environment at 1 to 10 m. The strong hygroscopicity of the solutes in the droplet is capable of keeping the droplet with an equilibrium size in humid air, larger than that of a dried particle. Mathematical models were developed to predict the droplet nucleus size in both dry air and humid air, by simplifying the composition of one expiratory droplet to NaCl solution and suspended spherical particles. For a droplet with an initial diameter of 100 μm, initial NaCl concentration of 0.9%, and initial solids ratio of 1.8%, the droplet nucleus size was estimated to be 42 μm in an ambient relative humidity of 90% (25°C), which is 30% larger than it was in a relative humidity of 30% (25°C). A numerical model was also developed to predict droplet evaporation and dispersion in a constant turbulent buoyant jet. Droplets with initial sizes larger than 80 μm were predicted to deposit on the floor at a distance of ~1.25 m (~1.7 m for 60 μm) away from the mouth, while droplets with initial sizes less than 40 μm travelled to the end of the jet. A series of experiments was conducted to assess the characteristics of human exhalation airflows and thermal plume, using a full-scale test room and a breathing thermal manikin. The impacts of the ventilation system were illustrated by comparing the velocity distribution of the exhalation airflows and airflows induced by thermal plume. Further experiments employing two breathing thermal manikins were carried out to evaluate the interpersonal transport of the expiratory contaminants that were simulated by tracer gas. When the two manikins with the same heights were standing face to face at a mutual distance of 0.8 m, the exhalation airflows from the mouth of the source manikin could directly travel into the breathing region of the susceptible manikin, resulting in a high exposure. The high exposure decreased sharply with an increase in the mutual distance from 0.5 m to 1.0 m. Between 1.0 m to 3.0 m, the exposure by the susceptible manikin remained at a low and constant level. Numerical simulations considering droplet evaporation and droplet nucleus sizes were carried out; and the impacts of the parameters of droplet initial size, humidity, vicinity, ventilation conditions and synchronization of exhalation were evaluated. Fine droplets and droplet nuclei were predicted to travel toward the upper part of the test room, whereas large droplets tend to be deposited on the floor. With a high relative humidity, 95%, most of the droplets were deposited on the floor within 16 seconds. Meanwhile, all of the droplets evaporated to droplet nuclei and remained suspended in the air when the relative humidity was 35%. Mixing ventilation that supplied fresh air with a ventilation rate of 5.6 h-1 resulted in drafts and strong turbulence, which made droplets and droplet nuclei dispersed in the room. The average vertical position was higher than that when the ventilation rate was 3.0 h-1. Displacement ventilation led to the vertical temperature stratification in the room. The vertical temperature gradient could neutralize the buoyancy force and weaken body plumes and the vertical dispersion of droplets and droplet nuclei. The inhalation of the droplets and droplet nuclei by the susceptible person and the deposition of the droplets and droplet nuclei on the body surface of the susceptible person were investigated at mutual distances of 0.5, 1.0, 1.5 and 3.0 m. For one breath from the source person, 1,600 droplets were released. Three and 9 droplet nuclei were inhaled by the susceptible person at a mutual distance of 0.5 and 1.0 m, respectively. No droplet nuclei were inhaled at 1.5 and 3.0 m. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

No description available.

The indirect effect of aerosols expresses how changes in aerosols would influence clouds and cause impacts on Earth's climate and hydrological cycle. The current assessment of the interactions between aerosols and clouds is uncertain and parameterizations used to represent cloud processes are not well constrained. This thesis first evaluates a cloud activation parameterization by investigating cloud droplet number concentration closure for stratocumulus clouds sampled during the 2005 MArine Stratus Experiment (MASE). Further analysis of the droplet size distribution characteristics using the extended parameterization is performed by comparing the predicted droplet spectra with the observed ones. The effect of dynamical variability on the droplet size distribution evolution is also investigated by considering a probability density function for updraft velocity. The cumulus and stratocumulus cloud datasets from in-situ field measurements of NASA's Cirrus Regional Study of Tropical Anvils and Cirrus Layers - Florida Area Cirrus Experiment (CRYSTAL-FACE) and Coastal STRatocumulus Imposed Perturbation Experiment (CSTRIPE) campaigns are used for this task. Using the same datasets, the autoconversion rate is calculated based on direct integration of kinematic collection equation (KCE). Six autoconversion parameterizations are evaluated and the effect of turbulence on magnifying collection process is also considered. Finally, a general circulation model (GCM) is used for studying the effect of different autoconversion parameterizations on indirect forcing estimates. The autoconversion rate given by direct KCE integration is also included by implementing a look-up table for collection kernels. Although these studies add more variability to the current estimate of aerosol indirect forcing, they also provide direction towards a more accurate assessment for climate prediction.

The stability of drops forced by both wind and gravity is a fluid mechanics problem relevant to heat exchangers, fuel cells, and aircraft icing. To investigate this phenomenon, drops from 15 micro-liters to 400 micro-liters were placed on the rough aluminum (RA = 3.26 micrometers) floor of a tiltable wind tunnel and brought to critical conditions, when the drop begins to run downstream. Various combinations of drop size, inclination angle, and flow speed were employed. A measurement technique capable of measuring full 3D drop profiles was implemented to investigate the drops' evolution toward runback. The measurement requires the comparison of the speckle pattern captured by an overhead drop image with a corresponding image of the dry surface. Stability limits for 235 drops are measured as functions of drop volume and surface inclination. Drops experiencing airflow alone are found to shed at a Weber number of 8.0 +/- 0.5. From measurement sequences of reconstructed drop profiles, the evolution of contact lines, drop profiles, and contact angle distributions are detailed. Contact line integral adhesion forces are calculated from contact angle distributions and related to the forcing air velocity. Drops whose stability limits are dominated by gravity are found to exhibit significantly different evolution toward runback than those dominated by airflow.

Thesis (M.S.)--University of Delaware, 2007. / Principal faculty advisor: Kausik Sarkar, Dept. of Mechanical Engineering. Includes bibliographical references.

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Garimella, Srinivas; Committee Member: Fuller, Tom; Committee Member: Jeter, Sheldon; Committee Member: Lieuwen, Tim; Committee Member: Wepfer, William. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2007. / Rosen, David, Committee Chair ; O'Connor, Jerry, Committee Member ; Fedorov, Andrei, Committee Member.

L'opération de précipitation oxalique du plutonium dans les usines de retraitement du combustible nucléaire est délicate à mettre en œuvre en raison de la nature collante du précipité. Dans l'idée de pallier ce problème gênant vis à vis d'une production industrielle, le Laboratoire de génie chimique et d'instrumentation du CEA Marcoule propose de réaliser cette opération en colonne pulsée à garnissage. Le précipité est alors confiné à l’intérieur des gouttes de l’émulsion et suffisamment loin des surfaces de l'appareil.Cependant si les surfaces en contact son en acier inoxydable, l'appareil s'encrasse invariablement. La thèse s'insère alors dans une démarche de compréhension fine de ces mécanismes d'encrassement. Bien que les travaux réalisés balayent l'ensemble du problème posé, la thèse est essentiellement centrée sur l’analyse du rebond des gouttes de l’émulsion avec les parois de l'appareil. Les résultats acquis permettent d’enrichir la base de données de la littérature dans une configuration peu usitée tout en ciblant les paramètres clés de ce type d'interaction. Les résultats montrent qu'utiliser en première approche, une colonne pulsée non optimisée et conçue intégralement en acier inox ne peut convenir pour réaliser l'opération de précipitation de radionucléides. Cette précipitation peut cependant être menée en s'orientant vers une technologie différente et brevetée à l'issue de cette thèse. Ce dernier point doit cependant être nuancé car l'exploration à des débits industriels de production n'est pas encore acquise. D'un autre coté, cela peut constituer un enjeu intéressant de génie des procédés. / The process dedicated to the oxalic precipitation of plutonium is very sensitive to the high sticking behavior of the produced precipitates. Therefore, the laboratory of génie chimique et instrumentation based in Marcoule in France puts forward the idea of carrying out the process in a pulsed column. In this way, the precipitates is confined inside in the droplets of the emulsion, far from the surfaces of the apparatus. Nevertheless if those surfaces are made of stainless steal the fouling of the column is inevitably observed. The thesis also introduces the concept and tools dedicated to a fine understanding of the fouling issue. Though the work carried out scans the whole issue, the thesis mainly focuses on drop bouncing. the results provide experimental data in a low-studied configuration and target the key parameters driving th bounce. The application of the these results point out that using an unoptimized stainless steal pulsed column for the precipitation of radionucleides does not prevent from the fouling. The process could still be carried out using another technology patented during the PhD. This last poitn needs more investigations. Especially, the CEA has work on the scale-up steps to design an apparatus wich could be able to porcess industrial flow rates. Bsides ths might be an interessing issue in process engineering.

On considère dans cette thèse plusieurs situations dynamiques concernant des gouttes accrochées à des fibres,en mouillage total. Ces gouttes funambules se rencontrent au moment de la fabrication industrielle de laine de verre quand la colle projetée à l’état liquide lie les fibres de verre composant l’isolant thermique.Dans une première partie, nous étudions l’évolution spontanée d’une jonction liquide entre deux fils : une goutte mouillante aligne et attire les fibres qu’elle connecte et nous caractérisons la dynamique et l’intensité de ces interactions capillaires. En outre, si deux fibres se recentrent avec un angle aigu, une goutte à leur intersection s’étale dans le coin tandis qu’un excès de liquide progressera en sens inverse entre les fibres jusqu’au point où leur espacement est de l’ordre de leur rayon. Nous calculons cette distance critique et l’observons au sein de la laine de verre, révélant l’étalement possible du liant industriel avant séchage. L’influence de l’élasticité des fibres est discutée.Dans une seconde partie, nous proposons deux méthodes forçant le déplacement d’une goutte funambule isolée.Premièrement, un champ électrostatique établi entre une fibre conductrice et une contre-électrode provoque l’étalement irréversible d’une goutte isolante lorsque la surpression électrostatique l’emporte sur la surpression capillaire. Nous modélisons la dynamique de cet étalement diélectrophorétique comme un effet Marangoni. Deuxièmement,un flux d’air transverse à la fibre induit un mouvement de la goutte dans un sens aléatoire si le nombre de Reynolds associé dépasse la valeur critique où le sillage devient asymétrique. Nous modélisons la dynamique de cette translation comme un effet d’entraînement visqueux de la goutte par le tourbillon principal du sillage,alors que les interactions entre tourbillons expliquent la répulsion à longue distance entre plusieurs gouttes, leurs rebonds sur des obstacles solides ou leur capture par un obstacle placé en aval de l’écoulement. / This thesis deals with several dynamic situations involving drops hanging on fibers, in total wetting. Such drops can be found during the industrial process of glass wool manufacturing, as liquid glue is projected onto glass fibers in order to bind them and form the thermal insulator.In the first part, we study the spontaneous evolution of a liquid junction between two wires : a wetting drop makes the wires align and approach, and we characterize the dynamics and magnitude of these capillary interactions.Besides, a drop placed in the wedge between two fibers spreads in the corner, whereas an excess of liquid placed at the intersection spreads in the opposite direction until it reaches a spacing close to the fiber radius. We calculate this critical distance and observe it inside glass wool, revealing the possible spreading of industrial binder before it dries. The influence of elasticity is discussed.In the second part, we propose two ways to induce drop displacement. First of all, an electrostatic field between a conductive fiber and a counter electrode leads to the irreversible spreading of an insulating drop when the electricoverpressure exceeds the capillary overpressure. We model the dynamics of this dielectrophoretic spreading asa Marangoni effect. Secondly, a transversal air flow can induce the continuous motion of the drop in a random direction if the Reynolds number exceeds a critical value, at which point the wake becomes asymmetric. We model the dynamics of this translation as a viscous entrainment of the drop by the main vortex of the wake.The interactions between vortices are responsible for long-range repulsion between drops, their rebonds over solid obstacles and their capture by a downstream obstacle.